CONSTRUCTION AND

DETAILING
FOR INTERIOR DESIGN

KING
GO
NT

LAURENCE KING
First published in 2010
BLACK LOGO
KNOCKOUT
by
Laurence King Publishing

Ltd

361373 City Road

London EC1V 1LR
Tel +44 20 7841 6900
Fax +44 20 7841 6910
E enquiries@laurenceking.com
www.laurenceking.com
Second edition published in 2015
by Laurence King Publishing Ltd
Design 2015 Laurence King Publishing Limited
Text 2010, 2015 Drew Plunkett
Drew Plunkett has asserted his right under the Copyright, Designs
and Patent Act 1988 to be identified as the Author of this work.
All rights reserved. No part of this publication may be reproduced
or transmitted in any form or by any means, electronic or mechanical,
including photocopy, recording or any information storage and retrieval
system, without prior permission in writing from the publisher.
A catalogue record for this book is available from the British Library.
ISBN 978-1-78067-477-3
Designed by Olga Valentinova Reid
Printed in China

DREW PLUNKETT

CONSTRUCTION AND
DETAILING
FOR INTERIOR DESIGN

Laurence King Publishing

Contents
INTRODUCTION 6

CHAPTER 1: EXISTING
WALLS 12

CHAPTER 2: NEW WALLS 24

First principles

Basic principles

Basic principles

Communicating information

Loadbearing walls

Stud partitions

Sustainability

Masonry

Constructing stud partitions

Creating openings in
loadbearing walls

Joints in plasterboard sheets

Cavity walls

Reinforcement of junctions in
stud partitions

Lining external walls

Metal framing for stud partitions

Non-loadbearing walls

Skirtings
Alternative skirtings
Cornices
Shadow-gap cornices
Soundproofing internal walls
Fireproofing walls
Fireproofing metal columns
Installing services

CHAPTER 3: ALTERNATIVE
PARTITIONS 50

CHAPTER 4: DOORS 74

Curving walls

Basic principles

Building curves

Modern detailing for doors

Freestanding walls

Sliding doors

Floating walls

Fanlights

Base fixings for partitions

Glass in doors

Cladding floating partitions

Non-standard doors

Fixing methods

Fire regulations for doors

Invisible fixings
Glazed partitions
Frames for glazed partitions
Framing and beading
Joining glass sheets

CHAPTER 5: FLOORS 86

CHAPTER 6: CEILINGS 112

CHAPTER 7: FURNITURE,
FIXTURES AND FITTINGS 122

Solid ground floors

Basic principles

Basic principles

Suspended ground floors

Suspended ceilings

Portable workshops

Upper floors

Angled and curved ceilings

Base structures

Timber joists

Proprietary ceiling systems

Jointing techniques

Timber rot

Hanging methods for proprietary

systems

Decorative joints

Timber floor structure

Steel beams

Other considerations

Joining sheet materials

Veneers

Planning new structures

Edging veneers

Installing new floor levels

Aligning furniture edges

Raising the floor

Openings in floors

Fabricating elements on site:

built-in seating

Floor finishes

Furniture legs

Finishing materials

Floating furniture

Other considerations

Shelving

CHAPTER 8: STAIRS 142

CHAPTER 9: MATERIALS 158

CHAPTER 10: STRUCTURAL

PRINCIPLES 170

Basic principles

Timber

Introduction

Timber stairs

MDF

Stone and concrete stairs

Plywood

Materials in compression
and tension

Steel stairs

Plasterboard

Handrails and balustrades

Steel

Cantilevered treads

Aluminium

Spiral stairs

Glass

Glass stairs

Acrylic

Fire regulations for stairs

Fixings

Ramps, lifts and escalators

Orientation of structural elements

Cantilevers
Beams
Stability
Rule-of-thumb sizing

CHAPTER 11: A TO Z 182

Glossary
Resources
Index
Picture credits
Acknowledgements

6 Introduction

Introduction
Basic principles

Technology

Successful interior design depends on sound construction

and beautiful detailing. Creative conceptual thinking needs
creative practical thinking if the spirit of a project is to be
successfully expressed in the finished building. A strong
concept has to be carefully nurtured through the stages of
its development, and its success depends, ultimately, on the
right decisions being made about the materials used in its
making and the way they are put together.
It is often said that interior design is about space, and
undoubtedly the proportions of an interior volume are critical
to its success. Ultimately, however, the appreciation of that
volume will be determined by the colours and textures that define
its planes and, as crucially, by the details of its construction.
Designers, perhaps inevitably, develop a personal style,
the result of preferred ways of expressing the elements
walls, floors and ceilings that enclose a space. Inevitably
they evolve a personal vocabulary of construction details
that determine how these essential elements are connected
physically and visually. A good designer will constantly
aspire to modify these preferences, in response to the
particular context and content of each new project, and
the particularities of each project will require, and should
prompt, new ideas and variations on old ones. However,
the basic principles of sound detailing remain constant and
the most visually diverse construction details will, if they are
successful, have been built on an understanding of practical
fundamentals. It is these essentials this book will explain.

Another engineer, Auguste Choisy, writing in 1899, argued

that significant shifts in architectural style had in the past
depended on technological advances: the column and
beam shaped Greek Classicism, the arch defined Roman
structures, the dome was a key element in Byzantine
construction. If one considers the development of interior
detailing, it becomes clear that what were essentially
practical considerations shaped the conventions of interior
detailing. It also becomes clear that practical solutions were,
in turn, shaped by human beings instinct to embellish their
habitations. It is enlightening to see how familiar traditional
decorative elements all had an essential practical role to
fulfil, and, while that role determined their location, the
recognition that they should be elegantly resolved and
enriched became the primary aspiration of their makers.
The practicalities were taken for granted and hidden behind
visual extravagance. Sinead OReilly summarized the
essence of interior design as Scenery/Machinery/Scenery,
recognizing the imperative to conceal the necessities of
structure and services behind the aesthetic veneer that will
satisfy the aesthetic appetites of an interiors users.

Practical solutions and aesthetics

The engineer Peter Rice, probably best known for his
work on the Centre Pompidou in Paris, maintained that a
structure should not only be capable of fulfilling its loadcarrying responsibility but should also look capable of
doing so and thus satisfy the instinctive expectations of
anyone looking at it. This is an argument not for traditional
or lumpen construction, but for clear visual expression
of rational thinking in radical design a recognition that
practical solutions should inform and, in turn, be informed
by aesthetic decisions. The built outcomes of such creative
fusion may initially surprise or disconcert those who
encounter them but their inherent logic should ultimately
communicate with and convince all who see them. The same
rule applies for all scales of detailing. If the interaction of the
aesthetic and the practical is creatively resolved, the integrity
of the result will be persuasive.

Process
Production and construction methods define the potential,
and therefore the character, of interior components. Simpler
elements such as flat, plastered walls and ceilings are most
conveniently made on site. However, there were limitations
to the quality of finishing that may be achieved under site
conditions and there were areas of every building that were
particularly vulnerable to wear.
Skirting boards were evolved to conceal the necessarily
untidy junctions of floors and walls, which were, and are,
difficult to finish precisely and are vulnerable to foot damage.
Cornices smoothed over the angles between wall and
ceiling, which were also difficult to finish perfectly and liable
to crack as the floor above them flexed. These protective,
masking elements were normally manufactured away from
the site and, as hand skills evolved and machine production
grew more refined, they became vehicles for increasingly
intricate moulding and came to characterize the architectural
styles that pre-dated Modernism.

Introduction 7

Detailing today
What may now be perceived as the decorative excesses of the
pre-Modern era have largely disappeared from the vocabulary
of building, but the obligation to deal aesthetically with
the mechanics of construction continues to be the critical
consideration in the creation of any interior. It may be argued
that the Modernist reaction against applied ornament created
fundamental detailing problems. Tried-and-tested solutions
were rejected because pioneers of the new style failed to
see, appreciate and assimilate the practical principles behind
the decorative veneer, but enough time has now passed
and enough evidence of relative performances has been
accumulated to encourage a more inclusive attitude.
The traditional principle of the cover strip (see pages
6263 and 135) which generated skirtings and cornices,
architraves and thresholds remains valid but is augmented by
the Modernist shadow gap (see pages 4041, 4445 and
6263), a space between elements that creates the illusion
of floating planes while, at a practical level, minimizing visual
misalignments. Both may be applied, equally effectively, to
perennial problems.

Using this book

This book illustrates strategies and tactics for successful
interior construction but it does not suggest that these
are the only answers. Good interior detailing is bespoke,
an informed response not only to the practical demands
of a new interior but also to the physical characteristics
of the existing structure that will enclose it. However,
only knowledge of essential construction principles and
techniques will ensure that innovative responses to context
and content are soundly constructed.
In each chapter, detailed drawings demonstrate generic
solutions to the construction of new elements, and these are
offered as starting points from which the designer may begin
to evolve personal and project-specific variations.
While the simple fundamental sequences of
construction and methods for connecting and fixing
are likely to remain relevant for all proposals, materials
and dimensions can and will vary. Those materials and
construction techniques most frequently encountered in
existing structures will be described, and the implications
of amending them examined. Techniques for repair and
restoration will be identified, and the practical and aesthetic
implications of joining and juxtaposing old andnew
elements will be discussed.

In each chapter, text and diagrams will amplify

the principles and considerations that should underpin
all developmental design thinking, demonstrating and
explaining rational, economic underpinnings for the most
ambitious proposals and suggesting previously unconsidered
aesthetic opportunities.
The drawings in this book are concerned with
explaining first principles of construction, and not with
communicating the detailed minutiae of a particular project
to a contractor, so they are necessarily diagrammatic. Rather,
the drawings represent essential generic construction detail
and principles. They are not definitive and the serious
designer will want to evolve them in the context of each
project. Certainly all would need to have comprehensive
notes added. All are made to scale to ensure proportional
accuracy but, since the same detail can be realized
with different sized components, scales are not cited
and dimensions are omitted unless they are universally
applicable. Notes are edited for the same reason. In
production drawings there is no reason to add axonometric
views to plans or sections, except as rare one-off elaborations
of unique three-dimensional conditions, but they are
included here extensively for the purposes of clarity.

8 Introduction

First principles
The practical considerations that shape interior detailing
are not demanding. Designers have no need to worry
about the requirements of weatherproofing that burden
those designing the exterior skins and impose on them an
inflexible repertoire of obligatory solutions and a restricted
range of materials. However, as comparative freedom from
the most stringent practical considerations means that
decisions about interior details must primarily be made
for aesthetic reasons, it can be argued that this makes the
process more challenging because there are fewer practical
priorities to inform and focus decision-making.
The mechanics of construction need not be
complicated. Materials may be nailed, screwed, bolted or
glued together with broadly equal practical success, but the
final solution, which must withstand the close and sustained
scrutiny of an interiors occupants, must be rigorously
refined and it is probably safe to suggest that the best details
are simple ones. Simple detailing is also likely to result in
financially viable construction. Simplicity, however, does not
mean simplistic work, which is the result of lazy or shoddy
thinking. The fixing on site of the most ornate pre-fabricated
traditional mouldings was, and is, an essentially simple,
utilitarian operation but the result is extravagantly complex
and highly refined.

Specialist knowledge
Most designers develop an instinctive understanding of the
capacities of familiar building materials to meet practical
demands, and this intuition is refined progressively as they
see their work built on site, but an essential skill for any
designer is knowing when to consult specialists. While it is
often enough to follow established practice, rules of thumb
or ones instincts, sometimes, as with complex structures
or service installations, it is necessary to have a specialist
consultant to provide precise proposals and calculations.
The designers role is to make an initial proposal and then
to orchestrate specialist input so that the sum of their
contributions makes for a successful whole, one that respects
the aesthetic intention. Every designer should try to find
consultants who will bring their own creativity to the process
and it is usually foolish to ignore their advice.
New materials, and the techniques that relate to their
installation, are continually evolving. It is logical to consult
manufacturers about the performance of their innovative
products, or fabricators about the potential of their
processes. Both are usually keen to collaborate in the hope of
extending their market and adding to their experience and
expertise. Manufacturers, who once had to rely on brochures

to promote their products, are increasingly developing

websites and these provide extensive and constantly updated
information about performance and installation.
While every designer must have the essential core of
practical knowledge, it is not possible, or necessary, to acquire
intricate understanding of the entire range of materials and
techniques relevant to interior construction. There is seldom
a single practical answer and it is legitimate, and prudent,
to take specialist advice to inform choice. It is foolish and
time-consuming to invent something from scratch if there is
a tried-and-tested precedent. A collaborative solution is likely
to be more practically efficient and effective. The designer
can concentrate on ensuring that the visual refinement of the
proposal survives the rigours of production.

Working methods
Increasingly, the hand tools associated with traditional
building skills are being superseded by electrically powered
alternatives and batteries offer greater mobility than cable
connections to inconveniently situated sockets. Power tools
speed up the processes of cutting, drilling, nailing and
screwing and, for many operations, increase precision. Since
the greater portion of the cost of any project tends to be
for labour, any acceleration in working methods will lower
costs but an emphasis on speed should not lead, in the
comparative chaos of building sites, to expensive mistakes or
a compromise in quality.
Where feasible, elements of a project are likely to be
constructed off site in the workshops of contractors and
specialist subcontractors. This generally ensures a high
standard of work, and such items are generally brought to
site and installed late in the construction process to avoid
damage. It is important to remember that restrictive door
heights and widths, narrow stairs and tight corners may
compromise delivery; it is not unusual for elements to
be transported in manageable sections. It then becomes
important to identify acceptable locations for visible joints
and to design appropriate fixing techniques so that the
assembled components read as a single unit.
Since much of this pre-fabrication will be carried out
by specialist subcontractors, chosen for their expertise, a
designer should try to discuss proposals in some detail with
them before issuing drawings. It has become common
practice for designers to define the form, dimensions and
materials of their proposal and to leave decisions about
construction methods to specialist fabricators who will
produce their own drawings, which should, in turn, be
presented to the designer for approval before work begins.

Communicating information 9

Communicating information
Designers explain their intentions for construction with a
comprehensive set of drawings and written documents that
describe in detail their intentions to all the trades involved in
a project. While the need to deal with the making of larger
elements is obvious, ultimately even the simplest instructions
must be clearly communicated because it is precision of
execution that determines quality. What may seem obvious
to the designer who has been absorbed in the detailed
development of a project will not be clear to the contractor
called in after the formative thinking is done.

Feasibility
It is important when evolving methods of construction to
consider the feasibility of carrying out instructions on site.
Drawings made in the well-lit warmth of the design studio
have to be implemented in the often chaotic environment
of the building site. It is easy to draw idealized proposals
that are impossible to build. A designer must be able to
visualize the process of construction so that its stages may
be appropriately sequenced for example, surfaces cannot
be finished properly if they are inaccessible, but finishes are
liable to be damaged if applied too early in the work.
It is easy to overlook in the design studio considerations
that are embarrassingly evident in the reality of the site.
Dimensions of the entrance, for example, which are likely
to be no bigger than a standard door, should determine the
size of everything that is brought to site.

Designercontractor relationship
Production drawings, also referred to as working drawings,
provide the building contractor, and anyone else involved in
the construction process, with a comprehensive description
in drawings and words of the full extent and quality of the
work necessary to complete the project satisfactorily. They
should describe the materials to be used, their sizes and the
method for their assembly. They act as a formal record of the
details of the contractual agreement between a client and
builder, describing in comprehensive detail the extent, and
the quality, of the work to be carried out for the money agreed.
It is always desirable that the designer should take
responsibility, on behalf of the client, for approval of the
standard of work carried out on site, if quality is to be
assured and the unforeseen difficulties that may come to
light during construction are to be dealt with successfully.
Ideally, the construction process should be seen as a
collaboration between designer and contractor. It is in the
interest of both that work proceeds efficiently and quickly.
Both should be capable of fulfilling their own responsibilities
efficiently, and have a sympathetic understanding of the

problems that may affect the others performance. However,

when difficulties arise the designer must act as an arbitrator
to ensure, on the clients behalf, that the extent and quality
of the work matches that quoted for while also ensuring,
on the contractors behalf, that payment is made on time
for completed work and for extra, unanticipated work
that may have become necessary during the course of the
contract. Such extras are often the result of site conditions
not apparent during initial surveys, which are usually made
before any exploratory demolition can be carried out.
Sometimes they are the result of a clients requirements
changing. Sometimes they are due to a designers error:
it is usually sensible to admit to these mistakes, since
responsibility will be obvious and arguing otherwise can
only lead to a loss of credibility and trust.
A completed set of production information drawings
allows a contractor to estimate the cost of building work
and to produce a tender, which is the estimated cost of all
necessary work, including labour and materials. A client may
nominate a single contractor, often on the basis of a previous
successful collaboration, to carry out the work. If this is done
before, or early in, the design process it is usual for designer
and contractor to discuss the most effective and economical
way of constructing the work. Where collaboration during
the design process has not been possible, the designer must
advise the client on the fairness of an uncontested tender.
It is more usual for at least three contractors to tender
and for the one offering the lowest price to be given the
work. When the successful tender has been identified it is
the designers responsibility to check that the contractor is
capable of carrying out the work to a satisfactory standard.
This is particularly important if the tender is lower than
anticipated, which can suggest that the contractor may
have miscalculated or is too anxious to get the job they
may not have the reserve resources to carry out work to the
required standard or to deal adequately with complications
that may arise.

Cost
It is often hard to establish the cost of an interior project
accurately. When operating in new buildings the nature
of the work may be clearly defined and estimated, and
unanticipated work or significant amendments to the
contract should not occur. The estimating of costs in
existing buildings is more difficult. Complications are often
unforeseeable and emerge during the course of the work, as
existing finishes are stripped and difficulties exposed.
It is also in the nature of interior work that finishes and
construction details will be unique to a particular project,

10 Introduction

and therefore an accurate price depends on a contractors

perception of the intrinsic difficulties involved in meeting
unfamiliar demands rather than on rule-of-thumb estimates.
Contractors inevitably prefer to work with familiar materials
and techniques and are likely to submit an expensive quote
for a complicated job, to ensure that what may potentially
be more difficult work will be adequately rewarded and
unforeseen costs covered. The simple project will almost
invariably prove cheaper. One that strays from the familiar
will require extra commitment from a client, who may be
inspired to agree to an expensive option by a seductive
presentation but whose initial enthusiasm will weaken
if there are a succession of expensive, unanticipated or
unacknowledged complications. If creative ambition creates
problems it is appropriate that the designer be blamed for
the practical inefficiencies and overspending that result. A
designer persuading a client to commit to an ambitious or
innovative project must be prepared to spend more time
detailing and supervising the quality of its construction,
probably for the same fee as would be earned for a more
conventional proposal.
Clients always have a budget beyond which they cannot
or will not go. While they often have some capacity to
extend beyond initial estimates, there is usually a point when
it becomes apparent that it will be necessary to negotiate
details of the work with the contractor to reduce the overall
cost. The designer is crucial to this process because decisions
must be made about how savings will least prejudice the
aesthetic and practical efficiency of the finished project, and
only the designer has the overview and knowledge to resolve
compromises in materials and construction successfully.

Presentation of drawings
There is no room for ambiguity in production drawings.
They should be clear and, as far as possible, simple. Even for
the most complicated project, simple drawings will usually
signify well-resolved thinking: an economical and effective
solution, easily built and fit for purpose. They will reassure
contractors that the extent of the work is clear, and should
reduce the factor of financial safety that might otherwise be
built into a tender.
Project information can be distributed digitally,
reducing the delays that affect price or completion times.
The disadvantage is that the designer is under greater
pressure to respond quickly to unanticipated complications,
and given that such revisions can have a significant, but not
immediately apparent, impact on the whole project and its
cost, it is sensible to agree a reasonable amount of time for
consideration of each development. If a designer has given
evidence of general efficiency, been sympathetic to the

contractors problems and is confronting an unforeseeable

dilemma, it is reasonable to expect understanding in return.
As CAM (computer-aided manufacture) develops its
capacity to relate to CAD (computer-aided design), the
communication of instructions from designer to maker
has become increasingly streamlined and refined. CNC
(computer numerical control) technology now makes it
quite feasible to link a designers laptop in one hemisphere
directly to a fabricating machine in another. The computerprogrammed machine has no preference for straight or
curved lines. Variations of lengths and radii, which would
require time-consuming manual adjustments to machine
settings and templates, may now be infinitely adjusted on
the designers computer.
The maker whose job it is to interpret and implement
drawn instructions is relieved of those time-consuming
obligations and, for better or worse, the quality of the
finished object will depend primarily on the capacity of
the designer not only to produce the drawings but also to
understand precisely the nature of the finished component,
the appropriate range of materials and the nature of joints
and fixings. Consultation with the maker of an artefact
will be less important in the evolution of ideas, and will be
replaced by the advice of manufacturers about the practical
and technical performance of their products.
It is reasonable to assume that software development
will identify and incorporate other practical, economic and
environmental data into the design and manufacturing
processes, and that increasingly specialized programs
will continue to evolve to deal with specialist needs. As
professional preferences and priorities become clear,
operating systems are likely to become increasingly
compatible. One significant example of this is BIM (building
information modelling), a process for the generation
and management of production information, and the
coordination of drawings made by all designers working in
all disciplines on a single project.

Sustainability 11

Sustainability
The designers approach
While the greatest contributions to energy conservation
are made in the external skins of buildings, there are
significant steps that an interior designer can take to
improve performance. They may appear modest, but if some
fundamental principles are integrated into design thinking
then the accumulative effect will be considerable. Insulation
of external walls, floors and ceilings, and the insertion of
double glazing where possible, will reduce fuel consumption.
This is no more than any conscientious individual could, and
should, do in many countries, it is a legal requirement for
all but the most delicate historic interiors. It is in the careful
consideration of construction and detail that the interior
designer may make a specialist contribution.
A designer can be selective in the materials specified,
and increasingly detailed information is available about
relative performances although, given the vested interests
involved, it is often wise to take a sceptical view of the
more extravagant claims. Decisions about materials and
techniques will often depend on financial considerations
and therefore ultimately belong to the client. However,
since sustainable building methods tend towards the
economical, a designer can, from the earliest stages of
project development, set an appropriate course. In the end
the most effective contributor to sustainability is longevity.
Sound construction and detailing can eliminate the need to
repair and replace.
Simple detailing, if combined with economical use of
materials, will go a long way towards satisfying concerns
about depredation of natural resources. While it is important
for designers to become knowledgeable about the
sustainable status of the more exotic building materials, and
to abide by laws and guidelines governing their harvesting
and acquisition, it is perhaps more important to employ

familiar, proven options intelligently and sparingly to

minimize a greater cumulative effect. Overly complicated
or pointlessly elaborate detailing wastes material and energy
and is unlikely to be robust enough to withstand heavy use.

Standard sizing
Components in the building industry tend to conform to a
range of standard sizes. For example, most sheet materials
are 2400mm x 1200mm with variable standard thicknesses.
This is beneficial for both manufacturers and designers as
it creates compatibility and makes repair and replacement
easier, cheaper and faster. If fixings that allow dismantling
with a minimum of damage, such as nails and screws, are
used then elements may be recycled. While even minimal
damage may preclude their reuse as finishing materials, it
will not affect reuse as substructure.
Standard sizes also provide a useful first reference
point in decision-making. It always makes sense to reduce
labour and material costs, so it is logical to cut a sheet of
1220mm-wide plywood into 305mm-wide strips, resulting
in three cuts and four units, rather than 310mm strips,
resulting in three cuts for three units and a 290mm-wide
strip of waste material.
Digital technology can significantly contribute to
the reduction of waste. It now eliminates the need to
make cutting templates by hand and also calculates how
to maximize the number of components, regardless of
size or shape, that may be cut from a standard-sized
sheet. Since the computer on which a proposal is created
can be remotely linked to the machinery that will make
it, no human intervention or interpretation is required
in the production process, standards are assured, and
transportation and travel costs (with their related carbon
debt) are reduced.

1200

STANDARDIZATION

1200
2400

1200

1200
400

900

1200

600

1200

If designers use, from the outset of

the design process, the standard
dimensions of components
manufactured for the building
industry as a basic module in their
planning, waste is minimized.
Widths of sheets are multiples of
400mm, which is the standard
spacing for framing and joists.
The 2400mm height of a sheet
determines the optimum height
for new rooms. Lengths of timber
come in multiples of 300mm.

CHAPTER 1 EXISTING WALLS

014 BASIC PRINCIPLES

015 LOADBEARING WALLS
016 MASONRY
018 CREATING OPENINGS IN LOADBEARING WALLS
020 CAVITY WALLS
022 LINING EXTERNAL WALLS
023 NON-LOADBEARING WALLS

14 Existing walls

Basic principles
Existing walls may be loadbearing or non-loadbearing.
Loadbearing walls divide spaces, but are also responsible
for supporting the construction above them. Nonloadbearing walls are responsible only for the subdivision
of spaces. Before making alterations to either, it is
crucial to consider the implications of any change. This
is particularly important in buildings with multiple
occupancy, where mistakes may result in damage to the
property of neighbouring owners that must be paid for
by the client or contractor.

and will allow the use of lighter, non-loadbearing walls

for the subdivision of areas.
There is no guarantee that existing structures will be
able to deal with additional loadings, and it can often be
difficult, even with the help of a structural engineer, to
prove the capacity of existing structures to cope. There
are always options, but these will inevitably increase costs
and affect the viability of a project.

Construction techniques
Both types of wall can use techniques of monolithic or
framed construction. In the first case, the wall probably
made of standardized units such as brick, block or stone
bonded with mortar will have an equally distributed
loadbearing capacity across its length. In the second,
framing elements located at regular intervals along the
length of a wall will focus the loading at those intervals

MONOLITHIC FLOOR SLAB

LOADBEARING WALLS

LOADBEARING WALLS:
CONCRETE FLOORS
A concrete floor, cast in situ,
will act as a monolithic slab and
require support on all its sides.

Loadbearing walls 15

Loadbearing walls
It is comparatively simple to identify a loadbearing wall.
If it aligns directly with a wall or walls on an upper
floor then it is likely to be transferring their weight to
the foundations. If it is removed, these upper floors will
collapse. Loadbearing walls will also support floors and
roofs. All walls surrounding a monolithic concrete floor
slab, particularly if the concrete has been cast in situ, are

liable to be loadbearing, but where support for the floor

depends on concrete or metal beams or timber joists,
then only the walls that support the ends of these will be
supporting the floor. The location of such beams may be
indicated by the presence of piers, or attached columns,
which increase the area and therefore the loadbearing
capacity of a wall at the points where the beams meet it.

LOADBEARING WALLS: BEAMS

When beams are used to reduce
the specification and size of
floor members, the load will be
concentrated where beams meet
the wall. Often piers (embedded
columns or projecting masonry
sections increased in size to
take the extra load) indicate the
location of beams and the points
where support must be retained.

FLOOR SLAB

STRUCTURAL BEAM
LOADBEARING PIER

16 Existing walls

Masonry

Flush mortar joint

Bricks are probably the most common material used to

construct loadbearing walls. They are made in standard
sizes the most common is nominally 215mm long,
102.5mm wide and 65mm high. The mortar joints that
bind them are nominally 10mm, so that in calculating
the dimensions of an area of brick wall, brick length plus
joint (225mm) and height plus joint (75mm) become the
basic modules. Unless necessary for structural support, it
is unusual to use brickwork in an interior. It is heavy, often
needs new concrete foundations, and wet mortar joints
must be allowed time to dry, holding up progress on site.

Bonds

Weathered MORTAR JOINT

Vertical mortar joints do not usually line through. This

increases the structural cohesion of the wall. In the
simplest 102.5mm-thick wall, bricks overlap by half their
length, and in thicker walls, typically 215mm or 327.5mm
wide, some bricks will be laid end-on to the face of the
wall to increase lateral cohesion. Abrick with its long side
exposed is called a stretcher and an exposed short side is
a header. The various brickwork patterns are known as
the bond and may be exploited for decorative effect.
A horizontal line ofbrickwork is known as a course.

Joints

KEYED MORTAR JOINT

There are various different ways of finishing mortar

joints. The most common internal, and external,
method is to finish the mortar flush with the face of
the brickwork. Weathered and keyed joints are used
externally to shed rainwater from the face of the wall
while creating a shadow that emphasizes the joint. If
water collects on an exposed horizontal brick surface
it facilitates penetration of the porous core, which will
be fractured when the water freezes. A squared-off or
recessed joint, which would collect rainwater if used
externally, may be used to emphasize the joint in new
internal walls. It is essentially a decorative device.

Pointing

Recessed MortaR joint

The careful finishing of mortar joints is referred to as

pointing and is normally carried out using a pointing
trowel. In older construction, mortar joints are frequently
weak particularly when traditional lime-based mortars
are affected by damp, which can cause mortar to soften
significantly. It is normal to rake out defective mortar
and re-point the joints. Usually modern cement-based
mortars will be used for this, but in restoration work, or
when new and existing joints must be matched visually,
lime-based mortars must be used.

Masonry 17

Brick slips

Plaster

When it is not feasible to use a solid brick wall, the visual

effect may be achieved with brick slips 20mm-thick
fired clay tiles of the same length and height as normal
bricks that may be fixed to plywood sheets on wooden
framing. The joints can be filled with mortar to complete
the illusion. When bricks or brick slips are used purely as
decoration it is possible to eliminate the interlocking and
overlapping of the bond, lining through all mortar joints
as an expression of the non-structural nature of the wall.
It is important to provide enough edge support, such
as a perimeter steel frame, to ensure structural stability.
Thin plastic sheets, moulded to represent both brick and
mortar, may be easily fixed to a suitable base, but tend to
sound unconvincingly hollow on impact.

Often, bricks used for internal and external walls of a

building shell will be concealed behind 1013mm of
plaster to provide a perfectly smooth surface for painting.
Textured finishes are available, for application by both
hand and machine. While an existing plaster finish may
be retained and repaired, it is not unusual for extant
areas to be removed to expose brickwork patterns and
texture as a decorative finish. Removing plaster, usually
by chipping it from the brickwork using a hammer and
chisel, can be time-consuming. Fragments stick to the
brick, but can be removed by wire-brushing or pressurewashing. The exposed face of brickwork will normally be
finished with a clear sealant to eliminate dust and darken
its colour.

tip Clues in the bond

It is often possible, by looking at the bonding
pattern of a brick wall, to determine not only
its likely thickness but also whether or not it
is loadbearing.
This is particularly useful with walls, such
as those dividing adjacent properties, that
have no windows or doors to reveal their
thicknesses.
In modern construction, external brick
walls are almost invariably of cavity construction and therefore the face of each skin
will read as lines of stretchers (known as
stretcher bond). However, windows and
doors will still reveal overall thicknesses.
Traditional cavity walls are generally 250mm
or 275mm thick.
When stretchers and headers alternate,
whether vertically (English bond) or in horizontal courses (Flemish bond), it is safe to
assume that the wall is at least 215mm thick
and therefore likely to be loadbearing.
In a party wall (one shared by two abutting
buildings), headers indicate a thickness of at
least 215mm and that it is therefore feasible
to build structural elements into the shared
wall up to half its width.
A loadbearing wall, particularly on the
lower floors of a high building, may be
thicker than 215mm, but that will not be
clear from the bonding pattern.

SECTION

ELEVATION

STRETCHER BOND

SECTION

ELEVATION

ENGLISH BOND

SECTION

ELEVATION

FLEMISH BOND

18 Existing walls

Creating openings in
loadbearing walls

SINGLE LINTEL

There will seldom be any need for an interior designer

to contemplate making door or window openings in
external walls, particularly as the most stimulating
interior projects are often generated by the need to
overcome the awkward locations of such existing
elements. However, it is possible to remove sections of
loadbearing walls, replacing them with a beam resting on
stable support points, but it is prudent to take specialist
advice from a building surveyor or structural engineer
on anything other than the simplest interventions. An
interior designer is not expected to have, and has no
need to have, expertise in this area, just as the surveyor
and engineer will have no capacity for the creation of
successful interiors.

Door lintels

DOUBLE LINTEL

TRIPLE LINTEL
LINTEL WIDTHS
Standard pre-stressed concrete
lintels will support a 102.5mmthick brick wall. For wider walls,
lintels of this standard width
may be aggregated to match
the standard widths of brick and
blockwork walls.

It is generally a simple matter to make door openings

they are unlikely to be wider than 900mm. Normal
practice is to remove the section of brick- or blockwork
and insert a precast reinforced-concrete lintel across the
gap. Two pockets on either side of the head, probably no
greater than the length of a brick, will provide support
for the lintel. The lintel for a single door opening will
probably be a single brick course deep and one brick
high to make re-plastering of the area simple. Greater
spans require deeper lintels, but it is convenient if these
increase by the depth of a brick course to make their
integration into existing brick courses simpler. Standard
lintels, suitable for designated spans, may be bought off
the shelf from builders suppliers, and their depths will
correspond to brick coursing. For walls more than a brickwidth thick, it is normal to insert as many lintels as it
takes to match the width of the wall.

Creating openings in loadbearing walls 19

When a bigger opening is required, the principle

of making the opening and inserting the lintel will
be the same but, because the loading is greater, it will
be necessary to spread the load over a greater area of
supporting masonry. All structural building materials
have a designated bearing strength, which is the weight
they can support before crumbling, cracking
and collapsing. This figure is recognized for the purposes
of structural calculations by the statutory bodies
responsible for approving new construction.
The calculation is a simple one. The dead load, or
the weight of the structure itself, and the superimposed
weights of occupants and their equipment are divided by
the bearing strength of the supporting material, which
gives the area necessary to support the combined loads.
The length of lintel is calculated by dividing that area
by the width of the supporting wall. While designated
bearing strengths are precise for newly manufactured
products, there is a high factor of safety for those
relating to existing materials, which can make justifying
proposals difficult.

Steel lintels
These offer an alternative to concrete, but their
comparatively smooth and impervious surfaces do not
provide as satisfactory a key for the mortar that will bond
them to the brickwork. Steel lintels are more normally
used within steel-framed construction, when they can be
bolted to steel-supporting elements through pre-drilled
holes in both components. Drilling off site in workshop
conditions allows great accuracy in the assembled
structure, but requires a similar level of accuracy in the
measuring of the site conditions, since there is little
opportunity for on-site adjustment.

SUPPORTING AN OPENING
The overlapping of bricks created
by standard bonds provides
structural support by directing
the loading of the wall area above
to the flanking walls. Only the
triangular area over the opening
requires direct support.

20 Existing walls

Cavity walls
Traditional external masonry walls were solid. They could
provide appropriate structural support, but offered less
protection against the penetration of moisture, whether
from rain or as rising damp drawn by capillary action
from the earth below and around the walls base. The
standard solution is now to build external walls as two
skins, separated by a cavity of about 50mm. Galvanized
metal or plastic wall ties, built at regular horizontal and
vertical intervals into corresponding horizontal courses,
bind the skins into a monolithic structure, and twists
at the midpoint of each tie shed water and prevent it
from reaching the inner skin. Impervious insulation
compounds, pumped into the cavity to improve thermal

performance, will also help to prevent the passage of water

to the inner skin, if intact. Fissures can act as conduits,
carrying water to the inner skin. Inner skins, which do not
have to withstand rain, may be built with concrete blocks,
which can have better thermal qualities than brick.
In solid-wall construction, it is difficult to identify
the source of damp since moisture, unhindered by a
cavity, can transfer to the inner surface at any point. This
problem may best be prevented by adding an impervious
skin to the entire external or, more usually, internal face
of the wall.
It is useful to understand the principles
underpinning the construction of openings in external

OUTER SKIN OF
CAVITY WALL

OUTER SKIN OF
CAVITY WALL

PLASTER

PLASTER

INNER SKIN OF
CAVITY WALL

INNER SKIN OF
CAVITY WALL

DAMP-PROOF
MEMBRANE

DAMP-PROOF
MEMBRANE

CONCRETE
LINTEL

CONCRETE
LINTEL

COLD BRIDGE

CONCRETE
LINTEL

METAL ANGLE
BEAD

METAL ANGLE
BEAD

TIMBER
WINDOW
FRAME

TIMBER
WINDOW
FRAME

GLASS

GLASS

MIN. 50MM

SECTION

SECTION

SINGLE LINTEL

DOUBLE LINTEL

Window-head detail. The single

lintel creates a cold bridge effect,
so that the inner face of the lintel
is significantly colder than the
outer, and results in condensation
and localized deterioration of the
plaster finish.

Window-head detail. Separation

between two lintels prevents
cold bridging. The impervious
damp-proof membrane conducts
moisture to the exterior and
seals the gap between lintel and
window frame.

Cavity walls 21

OUTER SKIN OF
CAVITY WALL

cavity walls so that damage resulting from new internal

work can be avoided, and existing defects may be
diagnosed and made good. Moisture ingress results in
areas of damp and the deterioration of internal finishes.
It can also lead to poor insulation, which can affect the
occupants comfort and waste heating fuels.
In cavity-wall construction, water ingress is most
likely around door and window openings, causing the
deterioration of frames and the compounds that seal gaps
between them and the masonry. Sealants can be replaced.
Where bricks close the cavity at openings, a vertical
impervious damp-proof membrane prevents moisture
passing to the inner skin; if damaged, it must be replaced.

VERTICAL
DAMP-PROOF
MEMBRANE
EXTERNAL SILL
MASTIC POINTING
GLASS

TIMBER FRAME
INTERNAL SILL

PLAN

PLASTER

GLASS

JAMB CONDITION
TIMBER WINDOW
FRAME

METAL ANGLE
BEAD

INNER SKIN OF
CAVITY WALL

A recess in the outer face of

the frame houses a mastic seal
between the frame and brickwork.

TIMBER OUTER SILL

OUTER SKIN OF
CAVITY WALL

TIMBER INNER SILL

CONCRETE SILL

VERTICAL
DAMP-PROOF
MEMBRANE
EXTERNAL SILL

MASTIC POINTING
INNER SKIN OF
CAVITY WALL

GLASS

OUTER SKIN OF
CAVITY WALL

TIMBER FRAME

PLASTER

PLAN

INTERNAL SILL
METAL ANGLE
BEAD
PLASTER
INNER SKIN OF
CAVITY WALL

SECTION

SILL IN CAVITY WALL

RECESSED JAMB CONDITION

Angled surfaces conduct water

away from the vulnerable junctions
of frame and brick openings. Drip
grooves in the underside of sills
prevent water running back into
the fabric.

Setting back the inner skin of the

cavity creates a slot for a mastic
seal between frame and brickwork.

22 Existing walls

Lining external walls

Single-skin construction, which in brickwork is seldom
more than 215mm wide, also means that there is no
insulating barrier between the outer and inner faces
of the wall. Moisture saturation of the wall means that
the lime mortar used in traditional construction may
become soft and lose its binding capacity. Internal plaster
is particularly vulnerable to moisture. Wooden door
and window frames are also vulnerable because solid
construction allows water to penetrate around the sides of
the frame without the opportunity for drying out offered
by the air circulation of cavity construction. Such timber
elements are more prone to rot, further accelerating water
penetration and general deterioration.

Damp-proof membranes
The solution is to separate interior and external walls in
effect to form an inner skin and to treat the existing solid
external wall as the outer skin. This obviously reduces
internal room dimensions, typically by 100mm.

Attached inner walls One option is to fix an impervious

waterproof membrane to the inner face of the existing
wall. This is usually a plastic sheet fixed in horizontal
strips with generous overlaps and sealed joints. The sheet
is held in position by timber battens nailed or screwed
to the face of the existing wall. Brickwork or blockwork
offers an easier and more reliable surface for fixings,
which are normally hard masonry nails applied with a
pneumatic nail gun. The space between battens may be

packed with insulation, either flexible fibreglass quilt or

rigid polystyrene sheet; the former is easier to cut to size
and install. Plasterboard or other sheet materials fixed to
the battens will provide an inner skin for decoration.
When an existing wall is subject to heavy water
penetration, moisture will condense on the outer face
of the membrane. In this case, it is considered better
practice to use a bitumen-impregnated corrugated sheet
against the existing inner wall surface, which will allow
air to circulate through its ridges. While it is possible to
plaster directly on to the inner surface of the lining, this
does little to increase the heat-insulating properties of the
wall, and it may be prudent to build a freestanding inner
wall packed with insulation, as described below.

Freestanding inner walls It is more effective to build

a second, freestanding inner wall using a wooden or
aluminium framing system clad with plasterboard on
its inner face. The skeletal nature of the supporting
framework leaves spaces that may be packed with
fibreglass or polystyrene insulation. The reduction
in floor area caused by the new wall may be critical.
It is not necessary to remove existing plaster, and the
new plasterboard linings will give a smoother and truer
surface than the old. This may, however, appear odd in
an older property where internal walls that do not require
lining may appear more characterful. The only solution,
to line existing inner walls as well, is expensive and will
eradicate further vestiges of character.
EXISTING NON-CAVITY WALL

TIMBER BATTENS

9.5MM PLASTERBOARD

9.5MM PLASTERBOARD

DAMP-PROOF MEMBRANE

DAMP-PROOF MEMBRANE

INSULATION MATERIAL

INSULATION MATERIAL

BASE OF METAL STUDWORK

EXISTING SOLID WALL

TIMBER SKIRTING

FLOORBOARDS
TIMBER FLOOR JOISTS

FREESTANDING INNER WALL

PLAN

A new plasterboard inner wall

face may be nailed or screwed to
timber battens, treated for rot and
fixed with masonry nails or screws
and plugs to the existing wall. The
external walls inner face can be
lined with a damp-proof membrane
held in place by battens, and the
cavity filled with polystyrene sheet
or fibreglass quilt insulation.

ATTACHED INNER WALL

SECTION

An existing wall may be dry-lined

by constructing a freestanding
stud partition against the inner
face. The insulation material
is protected from penetrating
moisture by a vertical damp-proof
membrane sandwiched between
it and the external wall.

Non-loadbearing walls 23

Non-loadbearing walls
The practice of using framed construction to provide
the basic structure for non-loadbearing walls is well
established. Traditionally, thin timber laths about 6mm
thick, 50mm wide and 1200mm long were nailed to
vertical timber posts, which were approximately 100 x
50mm and spaced at around 400mm centres, to provide
the necessary structure. The resulting slatted surface
was finished with three coats of plaster to a thickness
of approximately 13mm. Quantities of plaster oozed
between the battens and, when hardened, provided a
key to support the flat, finished plaster skim coat. This
method reduced the weight of new walls but was timeconsuming, and the economics of the modern building
industry have rendered it obsolete except in high-quality
conservation projects. When a historical interior is
protected by law, it is of course necessary to get approval
for all projected changes.

Repairing existing walls

Where small areas of traditional lath-and-plaster wall
must be repaired, it is possible to do this by removing
a section of damaged material, replacing it with 9mm
plasterboard and finishing this with a thin skim coat that
will bring the level up to match that of the existing wall.
It can be difficult to make a completely imperceptible
join between the old and the new in existing walls, and
the junction is prone to cracking because of the different
response of the various plaster types to temperature and
moisture. When making any alterations, it is important to

consider the compatibility of new and existing materials.

There are always likely to be problems associated
with joining new elements, which increasingly have
a machine-produced precision, to old ones, which
frequently have the imprecision of the handmade and
the idiosyncrasies that result from age. It is often a more
satisfactory practical and aesthetic solution to design a
visible gap between the two. It is, for example, physically
difficult to butt a new plastered partition up to a fairfaced
masonry wall, to achieve a pristine plaster finish against
the irregularity of masonry, and the visual crispness of
the new element will be compromised. The mechanical
precision of a metal stop moulding, by bringing a sharp
edge to the new plaster, can be a satisfactory solution.

Openings in non-loadbearing walls

Openings in non-loadbearing masonry walls present
fewer problems than those in loadbearing examples.
It may, however, be necessary with wider openings
to calculate the depth and length of lintel required to
support the wall area above the opening particularly
with irregular stonework, where there will be limited
cohesive interlocking of individual pieces.
With framed partitions, it is much simpler to make
new openings by cutting through the framing posts and
the less substantial wall material that they support. It is
generally sufficient to trim the opening with new timber
and to insert a new timber lintel. Dimensions for this
may have to be calculated for wider openings.

tip The rough and the smooth: Alterations to Existing Walls

The nature of the construction of new walls
or partitions means that they tend to be very
perfect objects, particularly when compared
to the more handmade and worn elements
of the original structure with which they
may come into contact. It is never a good
idea to try to emulate the idiosyncrasies of
old construction. The result always fails to

convince, and a better solution is to create

a small gap between old and new and, if the
new wall is plastered, to use an expanded
metal plastering bead to ensure a completely
straight and robust edge. It would be
sensible to paint the timber framing before
fixing the plasterboard, since access is
otherwise difficult.

EXISTING WALL
METAL PLASTER
STOP
TIMBER
FRAMING
PLASTERBOARD

PLAN

CHAPTER 2 NEW WALLS

026 BASIC PRINCIPLES

027 STUD PARTITIONS
028 CONSTRUCTING STUD PARTITIONS
032 JOINTS IN PLASTERBOARD SHEETS
036 REINFORCEMENT OF JUNCTIONS IN STUD PARTITIONS
037 METAL FRAMING FOR STUD PARTITIONS
038 SKIRTINGS
040 ALTERNATIVE SKIRTINGS
042 CORNICES
044 SHADOW-GAP CORNICES
046 SOUNDPROOFING INTERNAL WALLS
047 FIREPROOFING WALLS
048 FIREPROOFING METAL COLUMNS
049 INSTALLING SERVICES

26 New walls

Basic principles
In interior design projects, new walls are often referred
to as partitions, particularly when they are nonloadbearing. Partitions can be designed to carry loads
if existing foundations are capable of supporting the
additional weight or if new foundations are provided, but
this will cause considerable work, extend the length of
the contract and significantly increase cost. It should not
be undertaken lightly.

Bricks and blocks

Bricks or blocks, and certainly stone, are avoided in the
construction of partitions because they are heavy, and
this can be a particular problem with the subdivision
of an upper floor, which will often be incapable of
taking additional concentrated loading. The time taken
for the wet sand-and-cement mortar used in masonry
construction to dry also imposes delays that can be
critical in the viability of some projects.
Both bricks and concrete blocks come in a range
of qualities. If they are to be finished with plaster, the
quality of their exposed faces is not important. When
plastering, concrete blockwork which is faster to lay
because of its greater unit size will usually be favoured.
Where there is no significant structural obligation,
lightweight blocks (which are easier to handle) may be
specified. Masonry partitions may be left unplastered,
or fairfaced, which exposes not only the pattern of
the chosen bond but also the colour and texture of the
brick or block. With brickwork, variations are usually the
result of the different clays and firing times used during
manufacture.
It is, however, more usual to finish partitions with
13mm of plaster, applied in three coats, each of which
must be allowed to dry before the next may be applied.
This can cause additional delay. A different variety of
plaster is used for each of the coats.

Sizes Bricks have a standard size, 215mm (length) x

102.5mm (width) x 65mm (height), and are laid with
10mm horizontal and vertical mortar joints. Blocks
vary in size, but the most common size is 440mm long
x 215mm high. Their width varies from 50 to 200mm
in 50mm increments. There are various bonds, which
are the patterns created by the mortar joints, but by far
the most common is when the bricks or blocks overlap
by half their length (stretcher bond; see page 17). This
overlapping increases the strength of the wall.

Concrete
A concrete wall will exacerbate all the problems of weight
and construction time associated with masonry. It will
be particularly heavy and should really only be used
where this weight is useful for example, as a means of
reducing sound transference between areas. Concrete is
poured, when wet, into a mould, known as a shuttering
or formwork, which is normally a timber or steel frame
clad in plywood or metal sheeting that holds the concrete
mix while it dries. The shuttering must be constructed
on site, the concrete poured in, vibrated to eliminate air
pockets and left to cure, or dry. It can take three weeks
to gain 90per cent of its final strength, and the more
slowly it cures the stronger it will be. Long drying times
are unlikely to be acceptable in an interior project unless
justified by very particular practical requirements. Pouring
concrete is also a significantly more expensive procedure.
When the concrete has hardened, the shuttering is
removed. If the intention is to use the raw material as
the finished wall surface, it must be sealed to stabilize
the unavoidable surface dust. Pouring concrete in an
existing building shell creates practical problems that
may eliminate it as a viable option. If the proposed wall
is required to span between an existing floor and ceiling,
then the wet mix cannot be poured into the formwork.
It must be pumped through holes at as high a level as is
practical to ensure that it fills the void. It is difficult to
pack concrete densely at the top, and some patching is
likely to be necessary when the shuttering is removed.

Alternatives to concrete It is possible to use lightweight

concrete, in which the larger aggregate (normally stone) is
replaced by vermiculite, perlite or other less dense solids.
The time-consuming problem of pouring wet concrete
into temporary shuttering remains. Lightweight precast
concrete panels may also be used but the dimensions
of these are likely to be restricted by access to the site,
making visible jointing of panels necessary. This needs
tobe anticipated during the detailed design stages.
However, given that concrete in an interior is
likely to be chosen for its visual qualities rather than
its structural or sound-reduction capacities, there are
alternatives that will satisfy aesthetic ambitions. It is
possible to achieve the appearance, if not the weight
and solidity, of a concrete wall by applying a 13mm
sand-and-cement render to an expanded metal lath
that is supported on a lightweight stud frame. A3mm
skim coat of grey plaster on plasterboard will provide an
equally convincing facsimile. With both methods, the
finished face must be given a clear seal to eliminate dust,
and this produces a darker, slightly glossy appearance.

Stud partitions 27

Stud partitions
The stud partition offers a much quicker construction
method than brickwork, blockwork, concrete or the
traditional lath and plaster, with no lessening in quality
of finish but with reduced acoustic performance. The
first two coats of wet plaster are replaced by plasterboard
sheets that may either be finished with a 3mm skim of
plaster, which is quick to apply and dry, orbe painted
directly, after some simple filling of joints.

Plasterboard
Plasterboard sheets consist of a core of gypsum plaster
between two skins of paper. One side, the lighter
coloured, can be painted directly for a finished surface
or used as a base for a plaster skim coat; the darker side
also provides an absorbent key for a skim coat of plaster.
Sheets come in a number of standard sizes. The most
common is 2400 x 1200mm, and may be 9 or 12.5mm
thick. The 2400mm dimension determines the most
economical height of rooms in new buildings. This
standard height is encountered less frequently in older
buildings, but it is worth considering the feasibility when
constructing new enclosed areas within a taller space.
Longer sheets are available. Eliminating joints speeds the
building process and reduces labour costs.

STUD PARTITIONS
Wood or metal stud framing
can provide the structure for
lightweight internal walls.
Framing should be fixed to secure
elements walls, floors, ceiling
slabs or joists to ensure stability.

Plasterboard and skim technique

The basic framework of a stud partition remains the same
as for traditional lath-and-plaster construction, although
framing members are smaller in cross-section and more
smoothly finished. The skeleton framework is clad in
sheets of plasterboard to create a base wall surface, which
is then finished with a 3mm coat of plaster, called skim,
that visually eliminates joints and fixings. This thin coat
dries quickly and provides a smooth, comparatively nonabsorbent surface that is particularly suitable for painting.

Drywall technique
It is increasingly common to use the drywall technique,
eliminating a wet skim phase. This was originally evolved
to increase the mechanization of large-scale, repetitive
construction, reducing building time and labour costs.
It remains most effective in large projects with repetitive
subdivisions, which should ideally consist of multiples
of standard board sizes, and can also be effective in
simpler jobs because it eliminates the need for a specialist
plasterer. While the erection and finishing of drywalling
requires specialist tools and techniques, its speed makes
it cost-effective and, as long as the joints and the arrises
(sharp, straight edges) involved are not too many or too
complex, it will provide a satisfactory finish.

HEAD SUPPORT BETWEEN

JOISTS
When running at right angles to
ceiling joists, head plates should be
nailed or screwed at each crossing.
When parallel to joists, they should
be positioned directly under one
of them. When this is not possible,
bridging joists at 400mm centres
should be inserted to provide
secure fixing points.

28 New walls

Constructing stud partitions

Fixing plasterboard cladding
Plasterboard sheets are fixed to vertical and horizontal
framing, which may be lengths of either planed softwood
or very thin aluminium sheet, folded, creased and
dimpled to give it strength and rigidity. A structural
engineer can calculate the dimensions of framing
members and specify grades of timber and fixing methods
to meet statutory requirements for a structural wall
capable of supporting an upper floor level.
The skeleton frames that result are seldom wholly
rigid; it is not until the plasterboard cladding has been
fixed in position that the frame becomes stable. Although
plasterboard is brittle, the frequency of fixing, with nails
or screws at 150mm centres, spreads stress sufficiently to

ensure that there is no damage. The framing members are

stabilized by the rigidity of the sheet.

Standard sizing
While any size of timber may be used, it is standard
practice to use specialist softwood framing. This comes in
a number of sizes: the most common are 38 x 63mm and
38 x 88mm, usually in 2400mm lengths. These are specified
as CLS (Canadian Lumber Sizes). The rectangular sections
are planed on all four faces, have slightly rounded corners
and are pressure-treated for resistance to wet and dry rots.
Pressure treatment ensures that the preservative liquid
effectively penetrates the whole section.

CEILING LEVEL

HEAD PLATE

STANDARD STUD FRAME

NOGGING

Top, or head, plates and bottom,

or sole, plates are screwed or
nailed to a structurally stable
component (e.g. timber joists or
concrete floor slab). Vertical studs
are centred (400mm for 9.5mm
plasterboard and/or 600mm for
12.5mm) along the length of
a wall, and the regular spacing
ensures that vertical joints between
standard sheets are always
centred on, and strengthened
by, a stud. The centre of the final
two studs will vary in response to
the site dimensions, but should
not exceed standard spacing for
the wall. Noggings (horizontal
bracing timbers) provide lateral
support at 800900mm vertical
centres. A staggered position
makes fixing through the vertical
stud into the end of the nogging
simple. The centre of the final two
studs will vary in response to site
dimensions, but should not exceed
standard spacing for the wall.

VERTICAL STUD

BASE PLATE

FLOOR LEVEL

ELEVATION

Constructing stud partitions 29

FRAMING FOR OPENINGS

Structural openings for doors are
head plate
generally standard widths (700,
800 or 900mm), and the standard
height is 2000mm (see page 76).
Vertical framing members should
be regularly spaced to ensure noggings
even support for cladding sheets
regardless of the length of wall.
Any residual length which should
vertical studs
not exceed the basic centring
dimension should be treated
as a one-off to fit the particular
location. Centres for vertical studs
and the level of noggings should
be adjusted to suit the widths and
positions of doors.

sole plate

STRUCTURAL OPENING

PLAN

JUNCTIONS OF FRAMES
Corners are particularly vulnerable
locations within a stud partition,
subject to conflicting distortions
and movements within the two
converging walls. It is therefore
important to ensure that there is
enough framing to offer adequate
support to all plasterboard sheets.

VERTICAL STUD
PLASTERBOARD

HORIZONTAL
STUD

SETTING OUT OF VERTICAL

STUDS AT CORNERS
The presence of framing members
at every junction of the cladding
sheets ensures that faces of
abutting sheets are level, cracks
in skim coats of plaster caused by
impact and differential movement
are eliminated, and all joints in
plasterboard sheets are hidden.

30 New walls

Clout nails
Fixing to the softwood framing, when the surface is
to be finished with a skim coat, is traditionally by
galvanized clout nails. The galvanizing process, in
which a protective zinc alloy coating is added to mild
steel, ensures that the nails do not rust. This is important
because the expansion and deterioration of rusted
metal will cause the plaster covering it to be shed. The
large diameter of the head of a clout nail spreads its
grip across a greater area of the comparatively fragile
plasterboard surface.

Drywall screws
Self-tapping drywall screws, which are also resistant to
rust, are used to fix sheets to aluminium and softwood

studs. The screws are tightened until their heads are

slightly below the surface of the plasterboard, which
creates a shallow recess that is then filled with a
proprietary compound. This indentation is then sanded
smooth until it is level with the face of the plasterboard.
Screws are increasingly replacing nails, as electrically
powered screwdrivers now make them as easy to use
as nails, while the elimination of hammering reduces
impact damage to the stability of the framing and the
surface of the boards. This is particularly beneficial
when plasterboard is applied to both sides of a stud
frame, as hammering on one side can cause nails to
loosen on the other.

Constructing stud partitions 31

CONSTRUCTION SEQUENCE FOR

STUD PARTITION
Standard construction is simple.
1 The head and sole plates
are attached to the floor and
ceiling. The sole plate is cut to
accommodate the door opening.
2 Vertical members are inserted
on a module (400 or 600mm) to

suit the overall width of a standard

plasterboard sheet.
3 They are nailed in position with
timber framing or fixed with selftapping screws for aluminium. Nail
guns and electric screwdrivers are
replacing hand tools.
4 Additional horizontal bracing is
added at approximately 800mm

centres, subject to the height of

the wall.
5 The complete, assembled frame is
comparatively rigid but, because of
the simple nature of the butt joints
and fixings, is not wholly stable.
6 The addition of cladding sheets
and filling of the joints between
them makes a rigid monolith.

32 New walls

Joints in plasterboard sheets

SCRIM TAPE

3MM PLASTER SKIM COAT

9.5MM PLASTERBOARD

JOINT
CLS TIMBER
STUD FRAMING

PLAN

SKIMMING A JOINT
When the plasterboard sheets are
skimmed with a 3mm finishing
coat of plaster and the joint
reinforced with scrim tape, all
evidence of the fixing clout nails

9.5MM PLASTERBOARD

disappears. The joints can be

butted and, as long as the gap at
the joint is bridged by scrim tape
to eliminate cracking, there will be
no evidence of the join.

SCRIM TAPE

DRYWALL JOINT FILLER

Whether a plasterboard cladding partition is painted

directly, as in drywall construction, or given a skim
coat before painting, the joints between panels and the
external corners are vulnerable because the thin coat
of plaster or filler that bridges them is the weakest spot
on the wall surface and will crack with any movement
caused by impact or thermal expansion and contraction.
Every junction, whether vertical or horizontal, must
have framing behind it. This ensures that there can be no
local movement or distortion of unsupported edges, and
that the faces of sheets are perfectly aligned because they
are each fixed to the same framing piece.
The principles of dealing with joints and corners in
skimmed and drywall construction are essentially the
same, but specialist techniques and equipment have
evolved to deal with each.

Plaster skim finish

Straight joints The joint is bridged, and the plaster
reinforced by a 50mm-wide strip of scrim tape, a loosely
woven fine mesh. This now has a self-adhesive backing,
but it was traditionally fixed by being bedded in a thin
smear of plaster running the length of the joint or
internal corner before the skim coat proper was applied.

Internal corners The internal corner is comparatively

safe from impact damage, and vulnerable only to
differential movement of the converging walls. A line of
scrim tape along its length will be sufficient to deal with
the limited movement.
External corners The external corner is significantly

JOINT IN PLASTERBOARD
SHEETS
CLS TIMBER
STUD FRAMING

PLAN
DRYWALL JOINTS
In drywall construction the tapered
edges of plasterboard sheets meet
to form a shallow recess, into
which joint filler can be dressed
over a scrim-tape bridge. When
dry, the filler is sanded level with
the face of the boards before
painting.

more vulnerable to impact damage and needs robust

protection. In traditional construction, with a three-coat
plaster finish, corners were reinforced with a timber strip,
usually a quadrant moulding, that was better able to
withstand impact and gave a ready-made straight edge
against which the final coat of plaster could be finished.
Ashallow coat expanded metal angle bead now provides
a robust, straight line to define and protect the corner,
and acts as a guide for the plasterer. The perforated or
expanded metal mesh inner edge provides a reinforcing
key for the plaster. The bead is nailed or screwed to the
framing.
Similar profiles are used for three-coat finishes,
replacing the wooden quadrant, when they are described
as deep coat. Beads for both types come in a variety
of profiles offering options in locations where edges of
plaster would be both vulnerable and difficult to form
accurately, such as at skirtings and architraves.

Joints in plasterboard sheets 33

Drywall construction
Straight joints The abutting edges of boards may be
slightly tapered. The joint is bridged with a strip of
self-adhesive, heavy-duty paper, and covered with a
proprietary paste, which, when dry, is smoothed off and
sanded to give a finished face that is essentially flush
with the surface of the boards. Any minor irregularity is
visually eliminated when the surface is painted.
Internal corners The internal corner is again
comparatively safe from impact damage and perhaps
vulnerable to differential movement of the converging
walls. A line of scrim tape along the length will deal with
the limited movement.

External corners These are reinforced by means of a

strip of heavy-duty paper to which are glued two 10mmwide metal strips. When wrapped around a corner, with
a metal strip on each of the faces, the slightly raised strip
again provides a straight edge against which the finishing
compound may be dressed and sanded. The paper acts as
the exposed face, providing a continuous element that
matches the surface quality of the plasterboard and makes
a smooth surface for painting. The modest bulge that it
creates above the face of the plasterboard can be visually
eliminated by the addition and smoothing of the jointfilling compound.
Finishing When the finishing coats of skimmed plaster

CORNER JOINTING IN DRYWALL

CONSTRUCTION
Left
Corners in drywall construction
are reinforced by two metal strips,
glued to a robust paper tape.

or drywall filler are applied, the edge of the bead should

be just visible on the apex of the corner. After painting,
they will be indistinguishable from the rest of the wall
surface. Both can adapt to fit corners that are not exactly
right angles. The paper-based drywall component is
particularly flexible.

Right
The tape is folded with metal strips
on each side of the corner and
fixed with these strips against the
plasterboard. The uneven junction
is evened out with filler and, after
painting, disappears.

PAPER TAPE
METAL STRIP
METAL STRIP

STEP BY STEP Finishing drywall stud partitions

The final stage in drywall construction is a refinement of the
familiar building practice of filling holes and cracks. Holes
are the heads of screws, driven just below the surface of
plasterboard sheets, and cracks are the gaps, no more than a
few millimetres wide, between sheets. When joints and corners

have been bridged and reinforced with specialist tapes,

the filler paste is spread over them and sanded smooth and
dry, flush with the face of the plasterboard. After painting, all
evidence of fillings disappears.

Plasterboard sheets are fixed, with rust-resistant

screws, at 150mm centres to the stud frame.
The joints need not be tight or precise. Screw
heads will be driven slightly below the level of
the plasterboard.

The self-adhesive scrim tape is then placed to

bridge the joint.

The first filling compound is applied to fix the

tape in position.

This first application flattens the tape and also

provides a level base for the subsequent layers
of filler.

Filler is applied generously to allow for an even

distribution along the length of the joint.

The filler is worked along the joint so that it

finishes as flat to the surface of the plasterboard
as possible.

Heads of screws, sunken below the face of the

plasterboard sheet, are covered with dabs of
filler that are then roughly levelled by hand.

Sanding smooths and evens off the filler and

reduces it to the level of the plasterboard. When
painted, variation in level and texture will be
invisible.

10

The filler is sanded to eliminate the slight pitting

that follows the hand-levelling process, and to
reduce further any filler that remains above the
level of the plasterboard.

Continuous strips of angle beading define and

reinforce the sharp edges of this shelf and
recess.

36 New walls

Reinforcement of junctions
in stud partitions

VERTICAL STUD FRAME

(CLS TIMBER OR METAL)

Every junction in a plasterboard-clad partition must

have framing, timber or metal, behind it to align the
faces of abutting sheets and to eliminate cracks caused
by movement or shrinkage. The condition is easily dealt
with along the length of a wall by ensuring that joints
occur at a framing member. Corners, however, require
three vertical framing members that are themselves
nailed or screwed together to ensure that they do not
move unilaterally. They become a monolithic structural
element to which the four plasterboard sheets meeting
in the corner can be securely fixed.

PLASTERBOARD
3MM PLASTER SKIM COAT

ANGLE BEAD
ANGLE BEAD
Variations

GALVANIZED CLOUT NAIL OR

PLASTERBOARD SCREW

* 45 or 53mm Flange
Sizes
* 2.4mtr and 3.0mtr
METAL EXTERNAL CORNER BEAD

Applications & Design Features

INTERNAL ANGLE SCRIM TAPE

STUD PARTITION CORNER WITH

REINFORCEMENTS

PLAN

bead

Metal corner beads establish

straight arrises and protect against
impact damage on external
corners, while scrim tape reinforces
plaster against movement damage
in internal corners and at the joints
in plasterboard sheets.

plan

Strong and resilient bead design

for 2 and 3 coat applications. For
true, strong and straight externa
corner.
Installation Requirements
Plaster dab or galvanised nails.

Metal framing for stud partitions 37

Metal framing for stud

partitions
Advantages

SELF-TAPPING PLASTERBOARD
SCREW

METAL STUD FRAME

Aluminium framing was primarily developed for use in

large, repetitive projects that were designed to exploit its
standard lengths and assembly techniques, and it is most
effective if partition plans and sections are kept simple.
It is much lighter than timber, and therefore easier to
handle and transport. The standard sections have evolved
to use the smallest possible amount of material. The
strength and rigidity of the very thin aluminium sheet
are significantly increased by folded section profiles,
which are further stiffened by smaller-scale creasing and
dimpling. Unlike timber studs, metal alternatives do not
warp, shrink or split. The material is more expensive to
buy but quicker to erect by experienced labour, and is
therefore likely to be cheaper for large jobs.

Disadvantages
PLASTERBOARD

EXTERNAL ANGLE SCRIM TAPE

INTERNAL ANGLE SCRIM TAPE

Assembly involves specialist tools, but these are

comparatively simple and do not require particular
expertise. The specialized evolution of the system makes
variations from the standard more complex than with
timber stud, and, unlike with timber stud, the folded
hollow section does not offer the solid, flat surfaces for
simple, robust, one-off conditions. Designed primarily
as a lightweight solution, metal studwork does not have
the same loadbearing capacity as wood, and is therefore
unsuitable for supporting storage units.
Timber is a renewable material and its scrap is
biodegradable. Metal can be recycled, but the recycling
process is itself problematic. As with most questions of
sustainability, the answer is neither simple nor definitive.

PLASTERBOARD
METAL STUD FRAME

PLAN

METAL STUD PARTITION

CORNER

STANDARD METAL
COMPONENTS

A standard plan layout for metal

stud framing.

Metal framing members at a

corner and on a straight run.

38 New walls

Skirtings
Skirtings evolved to cover the junction of floor and wall
in traditional construction. It was impossible to achieve
a satisfactorily robust junction between the wooden floor
and plaster wall finish, and there was almost invariably
a gap between the ends and edges of floorboards and
the wall finish. The wooden skirting provided a resilient
masking for this weak spot, and its potential as a vehicle
for pre-fabricated decorative moulding was exploited in
traditional applications.
Skirtings developed into something complex that
could be tall in response to the generous proportions
of grander rooms, or intricate to inflate the status of
less spectacular spaces. High skirtings were usually
made from at least two components fixed together on
site. The line of the join was lost in the complexity of
the moulding, and a deliberate recess could disguise
the modest movement of joints that occurred with the
expansion and contraction of natural materials.
Modernist aesthetics dispensed with the idea of
the monumental skirting, and have encouraged the
possibility of eliminating the element altogether. The
twentieth century saw the rejection of decorative
moulding and the skirting became a flat length of timber
with, at most, a radiusing of the upper surface to protect
it against impact that might break a sharp edge. In its
most reduced form, it might be no more than 44mm high
and 13mm wide.

MDF skirting
The traditional material for skirtings is timber, but this
is often replaced by MDF (medium density fibreboard)
sections, which may be moulded to reproduce simpler,
traditional forms. MDF has the advantage of consistency
of section and performance, something that has become
difficult to achieve with cheap softwood mouldings,
which are prone to warping and splitting and frequently
contain knots. MDF versions are wholly stable and
often come ready-primed for the paint finish that the
material requires.

Plastic and metal skirting sections

Moulded plastic or pressed metal (usually aluminium)
skirting sections are frequently used with proprietary
partitioning systems and their hollow sections provide
a useful zone for wiring circulation. They tend to come
with a paint finish, and while this restricted palette may
be welcomed in expedient space-planning exercises, it
is unlikely to appeal to committed interior designers.
Some aluminium sections (skirting heaters) incorporate

hot-water circulation pipes and provide a space-saving

alternative to radiators and a more energy-efficient
alternative to underfloor heating for the even distribution
of heat throughout a room. They can be shaped to mimic
traditional mouldings.

Installing skirtings
Skirtings are fixed after floor and wall finishes (other than
paint and wallpaper) have been installed, and the abutting
edges of these can be left comparatively rough. A gap
between wall and floor allows movement without cracking.

Nails Fixing a skirting with nails is fast, but the impact

of driving them in can damage both the surface of
the skirting and the wall plaster. It is good practice to
have a timber ground, which is flush with the face of
the plaster, to absorb the impact and provide a more
substantial intermediary fixing between the skirting and
the stud frame. The head of the nail should be driven a
little below the surface of the wood using a nail punch,
and the indentation filled and the area sanded before
painting.
Screws These do not cause the same impact problem
as nails but are more time-consuming to use, requiring
more extensive filling and sanding. It is possible to drive
the head of the screw below the surface of softwood
skirting, but this tends to break the fibre of the wood and
force jagged shards above the surface that also require
filling and sanding.
Adhesive It is increasingly common to use a specialist
adhesive to fix skirtings directly to the plastered wall
surface. This eliminates the need to make good the local
damage caused by nails and screws, but is unsuitable for
walls that are significantly uneven. Almost all existing
surfaces, even those in recently constructed buildings,
will have some minor irregularities.

Visible gaps
Since existing floors are seldom perfectly level,
particularly where the ends of exposed floorboards meet
a wall, there is sometimes a discernible gap between floor
and skirting. If not too severe this may be accepted as
an inevitable symptom of age in an older building, but
where unacceptable for aesthetic or practical reasons it
may be filled, preferably with a proprietary flexible filler.
This, if applied carefully, sanded and painted, should be
visually unobtrusive.

Skirtings 39

CONSTRUCTION OF
CONVENTIONAL SKIRTING

3MM PLASTER SKIM COAT

PLASTERBOARD

A batten, usually 13 x 38mm,

supports the plasterboard sheet,
keeping it off the floor and
reducing contact with moisture.
A 3mm skim coat of plaster is
applied to the surface of the
plasterboard. A skirting, usually
softwood or MDF, is nailed or
screwed to the batten. The skirting
may also be glued directly to
the plaster if there is sufficient
continuous contact.

TIMBER SKIRTING (MAY ALSO BE

MDF, PLASTIC OR METAL)
SCREW
FLOOR LEVEL

SECTION

TIMBER BATTEN
SOLE PLATE

CONSTRUCTION SEQUENCE
The studwork is constructed and
the timber batten is fixed to it,
then the plasterboard and the
plaster skim coat are applied, then
the skirting.

40 New walls

Alternative skirtings
Shadow-gap skirting
It is feasible to dispense with the skirting strip and
to resort to the shadow gap option, but this does
not so easily overcome problems at the junction of
uneven floors and walls. The narrow gap, which is best
constructed using a proprietary metal plastering bead, can
be difficult to clean and plaster at the base and, because it
remains close to floor level, can be vulnerable to impact
damage. The construction sequence also becomes more
complicated since floor finishes need to be laid before the
walls can be plastered. The junction will be neater if the
edge of the floor finish is overlapped by the wall.

PLASTERBOARD
3MM PLASTER SKIM COAT

CLS SOLE PLATE (NAILED OR

SCREWED TO GROUND)
PROPRIETARY METAL PLASTER STOP
BEAD
PAR SOFTWOOD GROUND (NAILED
OR SCREWED TO EXISTING FLOOR)

SECTION

FLOOR LEVEL

CONSTRUCTION OF SHADOWGAP SKIRTING

The sole plate is nailed or screwed
to a planed softwood ground.
The plasterboard sheet is nailed
or screwed to the sole plate and
covers the junction between it and
the softwood ground. The lower
edge of the 3mm skim coat of
plaster is protected by an expanded
metal stop.

Alternative skirtings 41

Timber skirting with shadow gap

A more practical solution is to retain the gap but separate
it from the floor with a simple timber skirting section,
the face of which is flush with that of the plaster. The
plaster bead provides a clean, straight bottom edge for
the plastered surface and the timber skirting deals more
effectively with impact at floor level. If the skirting is
painted, it will be read as part of the wall. If it uses the
same wood as the floor finish and is left unpainted, it will
relate visually to the floor.

PLASTERBOARD
3MM PLASTER SKIM COAT

PROPRIETARY METAL PLASTER STOP

BEAD
CLS SOLE PLATE (NAILED OR
SCREWED TO GROUND)
TIMBER SKIRTING (MAY ALSO BE
MDF, PLASTIC OR METAL)
CLS SOLE PLATE (NAILED OR
SCREWED TO EXISTING FLOOR)

SECTION

FLOOR LEVEL

CONSTRUCTION OF TIMBER
SKIRTING WITH SHADOW GAP
An expanded metal bead creates
the gap above the softwood
skirting. It also defines and
protects the finished edge of
the plasterboard and skim coat to
the bottom edge of the plaster.

42 New walls

Cornices
Cornices essentially serve the same purpose as skirtings.
They mask the potentially unsightly junction of wall and
ceiling. In traditional lath-and-plaster construction it was
difficult to get a satisfactory right-angled junction, and
when floor joists also served as ceiling joists the junction
of wall and ceiling was vulnerable to movement caused
by loadings on the floor above. (Long joist spans were
particularly liable to deflection and vibration.)

Traditional cornice construction

Like skirtings, cornices were pre-fabricated, normally
made of plaster and cast in moulds that could be used
many times. They became a medium for elaborate
decoration. Moulded sections were made and fixed in
lengths. Junctions were comparatively easy to make good
in situ with fresh plaster, and imperfections tended to be
lost in the intricacies of the decorative detail.

Fixing methods Lighter lengths were fixed in place with

spots of plaster or dabs, but for most installations and
all those with deep, heavy sections nails or screws
provided initial support. Right-angled corner pieces,
which tended to be more elaborately decorated and of
fixed lengths, were joined by straight runs, which could
be cut to fit specific locations. The centre mouldings
were also cast and installed as one piece and, with the
introduction of gas and electric lighting, were useful in
masking connections and fittings.

Retaining existing mouldings Extant traditional

mouldings offer ready-made decorative detail and tend
to be prized by most clients. Good examples may also be
listed for preservation, and their retention and restoration
made a condition of planning permission. It is, however,
not unusual for sections of cornice to be damaged as
a result of deterioration of the building fabric or the
installation of modern services. It is not difficult, in
terms of detailing, to repair such damage, but the work
is expensive, invariably carried out by specialists who
make moulds from surviving areas and recast and refit
replacement sections.

Installing new cornices

It is easy to buy modern pre-fabricated cornice sections of
varying degrees of elaboration. The best-quality examples
continue to be of plaster cast in moulds, although plastic
versions offer a cheaper alternative and, because they are
lighter, are easier to fix with proprietary adhesives.
If cornices are used at all in modern construction
they tend to be simple, typically a concave quadrant

moulding, but they continue to serve the traditional

function of covering what is likely to be a crude junction
of wall and ceiling. Because they are planted on and
therefore project beyond the face of the wall, they offer a
distinct visual break, which is useful for making changes
in paint colour.

Right-angled junctions
If it is decided to omit the cornice in any of its forms
and settle for the unadorned right-angled junction, the
angle of wall and ceiling must be reinforced by scrim
tape, embedded in the skim coats of both. This will be
enough to eliminate cracking but does not make the
formation of a clean angle easier. With an imperfect
junction, the expedient solution is to paint the wall and
ceiling the same colour, so that the unevenness is not
further delineated. When colour differentiation is desired,
a solution is to take the colour of the wall up and over on
to the ceiling, to form a differently coloured border, or to
take the ceiling colour down on to the wall to create what
is, in effect, a two-dimensional cornice.

WALL AND CEILING JUNCTIONS

Traditionally, moulded plaster
cornices (1) covered the junction
of walls and ceilings because the
right angle caused construction
difficulties. Omitting a cornice (2)
conforms to Modernist principles
rejecting applied ornament.

Cornices 43

JOIST OR SIMILAR SECURE

ELEMENT TO SUPPORT HEAD
PLATE OF STUD PARTITION
BATTEN TO PROVIDE SECURE
FIXING FOR PLASTERBOARD
CEILING SHEETS
PLASTERBOARD

PRE-FABRICATED CORNICE
MOULDING (NAILED OR GLUED
TO PLASTER)
PLASTERBOARD
PLASTER SKIM COAT
HEAD PLATE OF STUD PARTITION

TRADITIONAL CORNICE

SECTION

A pre-fabricated cornice element

covers the junction between wall
and ceiling plaster that is likely
to crack because of differential
movement.

JOIST OR SIMILAR SECURE

ELEMENT TO SUPPORT HEAD
PLATE OF STUD PARTITION
BATTEN TO PROVIDE SECURE
FIXING FOR PLASTERBOARD
CEILING SHEETS
PLASTERBOARD
SCRIM TAPE
HEAD PLATE OF STUD PARTITION
PLASTER SKIM COAT
PLASTERBOARD

OMITTING THE CORNICE

SECTION

When it is considered that there

will be little differential movement
because of rigid construction and
small structural spans, the cornice
may be omitted and the plaster
junction will be reinforced with
scrim tape.

44 New walls

TIMBER JOIST

PAR SOFTWOOD GROUND

FIXED TO JOIST
CLS TIMBER BATTEN FIXED
TO JOIST

PLASTERBOARD
PLASTER SKIM COAT
PROPRIETARY SHALLOW COAT
PLASTER STOP

CLS TIMBER STUD FRAMING

FIXED TO GROUND

PLASTERBOARD

PLASTER SKIM COAT

Shadow-gap cornices

SHADOW-GAP CORNICE
The gap prevents cracking at the
junction of wall and ceiling.

SECTION

When the pre-fabricated cornice element is omitted it is

often difficult to get a clean, straight and even junction
between wall and ceiling. A shadow gap will, however,
provide a significant separation between the two so that
perception of inconsistencies between the vertical and
horizontal planes is minimized. Expanded metal plaster
stop beads reinforce the edges of both plaster surfaces
to eliminate fracturing and provide a visually dominant
straight edge.
The planed timber used for the exposed recess
provides a smooth surface for painting. The plaster stop
bead creates a straight line, at which the paint colour
may be changed. It is easier to paint the recessed ground
the same colour as the ceiling to avoid the difficulty of
precise finishing within a restricted area. Nevertheless, the
stop bead used on the ceiling edge will ensure a straight
line and enough differentiation between the ceiling and
the face of the recess to make a change of colour feasible.
A gap on the wall plane will imply that the ceiling is a
continuous surface that passes over the wall, while a gap
on the ceiling plane will imply that the wall continues
unbroken to the floor above.

Shadow-gap cornices 45

TIMBER JOIST

PLASTERBOARD
PLASTER SKIM COAT

PAR SOFTWOOD GROUND FIXED

TO JOIST
CLS TIMBER STUD FRAMING FIXED
TO GROUND

PLASTERBOARD
PLASTER SKIM COAT

ISOMETRIC OF SHADOW-GAP
CORNICE
The planed timber provides a
smooth surface for painting.
The metal plaster stops create
a straight line, against which to
finish the plaster skim coat.

46 New walls

Soundproofing internal walls

Weight of materials and rigid construction are the
most effective means of reducing the passage of sound.
Concrete walls and floors, cast monolithically, provide
the optimum solution but are only justified in specialist
projects. Bricks are second best, slightly superior to lighter
concrete blocks. However, in new interiors it is usually
impossible to use any of these, other than the most
lightweight blocks, because existing floor structures will
be incapable of taking additional concentrated loadings.
The 12mm finishing plaster needed adds more weight.

REDUCTION OF SOUND
TRANSFERENCE THROUGH
VOIDS
Sound can travel easily through
voids under floors or above
suspended ceilings. Where
transference is likely to be critical,
partitions should be built off the
original floor level and carried

Solutions for stud partitions

Stud frame with plasterboard cladding solves structural
problems but is not good for serious sound reduction.
The hollow construction exacerbates the problem, as
sound may be transferred comparatively easily across the
void and through the studwork that directly connects
both faces. The plasterboard cladding vibrates and
becomes asounding box for sound transmission.

Increasing cladding weight A skim-coat finish is better

than drywall construction, and two layers of plasterboard
on each face will increase the overall mass while also
reducing reverberation.
Specialist materials Hard surfaces and flat, parallel
planes, which generate reverberation, exacerbate noise
problems. Specialist plasterboard, identified by its blue
paper face, soft absorbent finishes and angled surfaces,
improve reduction. Transmission of airborne sound across
the voids in stud partitions may be reduced if absorbent
quilt material is inserted between framing.

Additional stud frame The studs themselves, in contact

with both faces, form an acoustic bridge. A solution is to
build two independent stud frames to break continuity.
This is comparatively complicated and takes up floor space.
Sound-masking It can be simpler to incorporate soundmasking, the introduction of unobtrusive background
sound in an environment, to reduce the clarity and thus
the capacity of overheard sounds to distract and irritate.

Planning In effect, all construction solutions other than

sheer mass and monolithic construction have limited
soundproofing success. It is better to deal with the
problem by clever planning, grouping and isolating areas
that need quiet using, for example, storage rooms as
buffer zones. Where a significant problem is anticipated,
it is appropriate to take advice from an acoustic specialist.

SECTION

above the new ceiling level, to

create a continuous barrier. In
this example, the size of framing
is reduced above ceiling level:
a demonstration of how a
practical necessity may be
aesthetically refined.

Fireproofing walls 47

Fireproofing walls

EXISTING CEILING
TIMBER FRAMING
TWO LAYERS
PLASTERBOARD

The basic requirements for fireproofing are, in many

respects, similar to those for soundproofing. Noncombustible materials concrete, brick and blockwork
obviously provide effective barriers. The materials and
comparatively fragile construction of stud partitions
present problems. Metal framing is non-combustible, but
the thin section is liable to buckle comparatively quickly
at high temperatures.

Design criteria

TWO LAYERS
PLASTERBOARD
ABSORBENT
MATERIAL

The basic principle of fire prevention and control is that

an outbreak of fire should be contained within the area
where it started. Basic plasterboard-and-stud construction
is adequate for the lowest level usually half an hour of
containment.
Escape routes, corridors and stairs are required
to provide a longer period of protection, usually an
hour. Precise requirements, however, depend on the
buildings function, its configuration and the number of
occupants. It is sensible to check at an early stage in the
design process the requirements of the appropriate local
authorities and to make sure that any proposals meet
their criteria, since many regulations are open to local
and individual interpretation.

Improving ratings The greatest problems are caused by

door and window openings, but when necessary the fire
rating of stud partitions can be improved by a number
of stratagems (these are described in the published
regulation documents), which are accepted as meeting
the required standards.
A skim coat improves the rating, as does with
more extreme requirements the use of two sheets of
plasterboard on the face of a partition. Some plasterboard
sheets, faced with pink paper, offer improved fire ratings.

Ducting Used for electrical cables, plumbing pipes and

TIMBER FRAMING
EXISTING FLOOR LEVEL
FLOOR FINISH

air-conditioning equipment, ducting can cause problems

when it passes between separated areas. This can occur
horizontally in walls and vertically between floors.
Usually these will be enclosed, for cosmetic reasons,
within fire-rated ductwork, and the means of isolation
is achieved without concern for its visual impact.
Manufacturers of air-conditioning equipment, which
presents the greatest risk, normally incorporate fire-stop
mechanisms into their products, and also offer specialist
advice.
It is important that the requirements are precisely
described in drawing and word to ensure that they are
exactly met and will pass local authority inspection.

48 New walls

Fireproofing metal columns

Steel columns, particularly I-sections, provide the most
commonly used structural components in interior projects.
They can be cut to size and curved with great accuracy off
site. They may be pre-drilled for bolting together on site,
and their erection is quick and comparatively clean. They
eliminate the time required by a concrete component to
set. They are strong in tension and acceptably capable of
dealing with compression loadings.
Their only weakness when compared with concrete
structural members is that they behave poorly in fire.
One solution is to give them a protective coating of
concrete. This requires the time-consuming building of a
mould, or formwork, however, into which the concrete
may be poured and allowed to set, which is difficult and
disruptive to carry out within the confines of an interior
site. Steel components can be more easily protected if
they are boxed within a plasterboard and stud casing.
It is also possible to treat steelwork with a paint
that will protect it sufficiently against fire to meet most
regulations, and this is an appropriate treatment where
exposed steelwork is an acceptable aesthetic solution.

Encasing beams in plasterboard cladding

Usually it is possible to protect, and conceal, steelwork
by casing it in a plasterboard skin, which will normally
provide an acceptable level of fire protection. Plasterboard
cladding is fixed to softwood framing and finished with
a skim coat.

Enhancing spaces This casing may be built tight to a

structural column, but it is worth considering if the plan
form should be modified to make a contribution to the
project as a whole. The casing may shift the perceived
structural axis to refine alignments within the interior,
or the random proportions of the structural member
may be reconfigured.
There is no need to attach the new framing structure
to the steelwork, as it can be satisfactorily fixed to floor
or ceiling. When there is a suspended ceiling with
inadequate fire rating, it will be necessary to encase the
steelwork above it to ensure complete protection over
the whole length of a column, although its visual impact
need not be considered.

BUILDING CLADDING
STRUCTURES FOR METAL
I-SECTIONS
A skimmed plasterboard column
cladding need not take its
proportions from those of the
steel stanchion it protects, but
can be sized to suit its context.

PLAN

PLAN

PLASTERBOARD

PLASTERBOARD

PLASTER SKIM
COAT

PLASTER SKIM
COAT

VERTICAL CLS
TIMBER FRAMING

VERTICAL CLS
TIMBER FRAMING

EXPANDED METAL
ANGLE BEAD

EXPANDED METAL
ANGLE BEAD

HORIZONTAL CLS
TIMBER FRAMING

HORIZONTAL CLS
TIMBER FRAMING

Installing services 49

Installing services
Services is a generic term for electrical, plumbing and
air-conditioning provision. Complex installations are
designed by specialist engineers, and the designer should
discuss and approve their intentions and ensure that the
equipment is successfully incorporated into the finished
building. The technicalities of small-scale projects are
likely to be decided by the tradesman responsible for
installation, and work should conform to the standards
set by the relevant professional organization. Again, the
designer is responsible for ensuring that provision is
made for the satisfactory installation and integration of
equipment.

Conduits Pipes and cables may be surface-mounted in

metal or plastic conduits where aesthetically acceptable.
Wiring lies loosely in conduits and replacement is easy if
new lengths are attached to old and both pulled through.

Order of installation
Installation is carried out in two phases:

First fix Installation of wiring, without power, and

pipework, without water, gas or oil, is completed before
finishes are applied. This is known as the first fix.

Second fix The installation and connection of switches,

sockets, lights, sanitary and kitchen fittings is completed
after the application of finishes and is the second fix.

Distribution of supply
Partition walls Essential service wires and pipes are
frequently circulated within the hollow core of partition
walls. They are passed through holes bored in the centre
of timber studs or cut out of metal studs at manufacture.

Masonry In brick or block walls, grooves, or chases, can

be cut mechanically or by hand into the face of the wall,
but both are time-consuming and messy.

Concrete Chases may be cut in concrete elements, but

the process is difficult. When new concrete walls, floors
and ceilings are being poured, it is normal practice to
incorporate within them a metal or plastic conduit,
hollow-cored, circular or rectangular in section, through
which wiring may be passed. Plumbing pipes are often
laid directly into the concrete floor screed.

Timber The voids within suspended timber floors are

particularly useful for the circulation of electrical wires
and plumbing pipes. When these have to run at right
angles to the direction of the joist, holes, which will
seldom have to accommodate pipes with a diameter
greater than 15mm, may be bored in the centre of the
joist, which at least affects its ability to deal with both
compressive and tensile forces.

METAL STUDWORK
In metal studwork, pipes and wires
are threaded through holes cut out
during manufacture (top).

METAL CONDUITS
Surface-mounted metal conduits
(above).

CHAPTER 3 ALTERNATIVE
PARTITIONS

052 CURVING WALLS

054 BUILDING CURVES
056 FREESTANDING WALLS
058 FLOATING WALLS
060 BASE FIXINGS FOR PARTITIONS
061 CLADDING FLOATING PARTITIONS
062 FIXING METHODS
064 INVISIBLE FIXINGS
066 GLAZED PARTITIONS
068 FRAMES FOR GLAZED PARTITIONS
070 FRAMING AND BEADING
072 JOINING GLASS SHEETS

52 Alternative partitions

Curving walls
It is generally good practice to use straight lines in all
aspects of construction. Curved walls may be spectacular
but they are more difficult to build, therefore more difficult
to do well and, almost inevitably, more expensive.

Curving materials
Materials are generally manufactured in straight lengths,
and flat planes and rectangular spaces tend to cope
more efficiently with furniture and equipment. It is
comparatively simple to cut two-dimensional curves out
of sheet materials. Plywood and MDF may be cut by hand
or machine with great precision. Other strand boards give
less exact edges, while plasterboard gives a broken and
fragile edge. Three-dimensional curves are more difficult,
but plasterboard, thin plywood and MDF, in their
standard forms, may be bent comparatively easily on site,
and all are also available in forms specifically designed
for curved surfaces. Plywood and MDF are manufactured
with grooves cut into one face, reducing resistance to
bending and eliminating both tensile tearing of the
convex face and compressive wrinkling of the concave.
A similar effect can be achieved by scoring one face of
plasterboard with a handheld knife.

Generally, the more elaborate the form the more

important it is that it should be pre-fabricated off site.
Three-dimensional curved walls are significantly more
difficult to construct, although just as the computer
makes them easier to draw so it can also translate drawn
forms into the data necessary for efficient machine
production.

Plans and layouts

It is also important, and sometimes difficult, to make a
satisfactory transition between a curved and a straight
line, and between two curves, even when the work is
carried out on site. The transition will work best if the
line from the centre of a curve to the point where it joins
a straight wall makes a right angle with it. Two curves
should intersect on the line that joins their centres.

Existing elements
The junction of new curved and existing straight walls
demands particular consideration. Here, it is not merely
a matter of the conjunction of different materials but of
the recognition that formal three-dimensional gestures
should be expressed elegantly and with precision. This

JOINING CURVES
The components of any complex
curved form should flow freely,
without any abrupt or awkwardly
angled changes in direction. The
transition will often work best if
the centre of the curve is at a right
angle to the straight elements.

PLAN

tip DONT DILUTE

Curved walls are used to create visual
impact, but if too many are employed in
one interior their effect will be diluted.
They will usually be more dramatic if
they are counterpointed by straight or
angled walls.

Curving walls 53

is most effectively achieved if there is visual separation

between the curve and the wall it joins, allowing
their distinctive forms to be clearly perceived. Where
the construction and finishing of the junction are
problematic, particularly when the space between the two
walls decreases, separation also eliminates the difficulty
of making a seamless transition between old and new.
Tactics for solving the problem are simple. The
first requires that the curve stops short of the wall it is
meeting and the second that it finishes parallel to it. In
both cases a recess is formed that may be used to house
a concealed light source to dramatize the separation or,
more prosaically, for storage.

Angling walls
Similar problems exist when an angled wall meets a
straight wall. In fact, when the angle between the two
is particularly acute the problem of accessibility for
construction and use of the space created is exacerbated.
It remains good practice to separate the two visually
and to close the gap between them by setting back the
connecting length of wall, again creating a recess that is
suitable for concealing a light source or for storage. In
the acute angle formed, it may make sense to sacrifice
unusable floor area by moving the enclosing wall face
until the area becomes negotiable.

RECESSES AND SHADOW GAPS

When angled and curved walls

meet straight walls it is a good
idea to leave a shadow gap or
recess. This avoids the considerable
problems of achieving a smooth
intersection of the two planes and,
as importantly, visually separates
elements, making them and the
junction between them more
significant. Three options are:
the curved wall stops short of the
straight wall (1); the curve runs
parallel to the straight wall (2); if
an angled wall is stopped short of
a straight wall, a difficult physical
and visual junction is avoided if
the resulting internal angle is too
acute and/or too deep the space
between the walls can be difficult
to finish or clean. This may be
solved if the short connecting wall
is located to allow room for both
operations to be carried out (3).

tip Seeing both sides

Since curves and angles are often
used to create significant visual
gestures, their effect on the area to
their rear must not be overlooked. It
is easy to create residual space on the
reverse that does not benefit from the
flamboyant curve, and it is therefore
worth considering whether the plan
should be squared off and a perimeter
created that is more sympathetic to
the straight lines and right angles of
furniture and utilitarian activities.

54 Alternative partitions

Building curves
Brickwork and blockwork
When making curves with bricks or blocks, the required
radius should be set out on the floor either as a drawn
line or as a physical template cut from cheap sheet
material. While it is possible to obtain curved bricks,
these are produced for a limited range of radii and are
not readily available.
It is standard practice to use conventional straightsided bricks or blocks so that the built wall emerges as
a series of short facets, each the length of an individual
brick or block. Plastering will convert the facets to a
smooth curve, but the success of the result will depend
on the plasterers skill and eye.

Stud partitions
To make curves in stud partitions, the basic construction
principles for a straight wall apply, but it is impractical to
bend a length of CLS timber to form sole or head plates.
The timber will resist bending, and it is more satisfactory
to cut plates from 19, 21 or 24mm plywood sheets.
These will also act as templates for the setting out of

vertical studs, which can be lengths of conventional CLS.

Plywood noggins can be cut as curves or from straight
lengths of CLS, of smaller section than the verticals
to allow the sheet material for the wall to assume the
natural curve determined by the regular spacing of the
verticals. Plastering will again create a smooth curve.
There are two options for the base to which plaster
may be applied. The first, expanded metal lath sheeting,
is designed to receive three coats of plaster, like a brick
or blockwork wall. The three-dimensional perforations of
the lath, fixed with galvanized clout nails or screws to the
stud framing, provide a key for the first coat of plaster,
some of which will ooze through the apertures. When
the plaster sets, the lath becomes rigid and forms the first
slightly rough and uneven version of the curve, which is
refined with the final two coats.
The second option is to use plasterboard and
to finish it with a conventional skim coat. Specially
manufactured plasterboard sheets can be bent to radii
as tight as 250mm. These can be difficult to obtain, and
for a small job, or one with only a few curved sections,

VERTICAL CLS
TIMBER STUD

SOLE, HEAD AND NOGGINGS

(CUT TO RADIUS FROM 19,
21 OR 24MM PLYWOOD)
EXPANDED METAL SHEET LATH
(CLOUT NAILED TO FRAMING)

PLYWOOD
NOGGINGS CUT
TO RADIUS

CLS TIMBER STUD FRAMING

(AT APPROXIMATELY 400MM
CENTRES)
12MM PLASTER (APPLIED IN
THREE COATS)

PLAN

TYPICAL CURVED PARTITION

Components and fixing methods
are the same as those used in the
making of straight lengths of wall.

FRAMING FOR CURVED

PARTITIONS
Vertical framing is of CLS studs.
Horizontal noggings may be short
lengths of straight stud of 19,
21 or 24mm plywood cut to the
correct radius.

Building curves 55

it is probably more expedient to modify standard sheets.

The convex face of a curve can be scored with lines at
approximately 50mm centres and cut vertical to the
direction of the curve. The skim coat will fill the V-shaped
grooves on the convex face.
While plasterboard is essentially a rigid and brittle
sheet material, it can be given a degree of pliability if
wetted until the gypsum core has been moistened. This
can be done effectively with a paint roller, and takes
about 15 minutes for adequate penetration. Itis then
possible to shape it around the armature of the stud
framework. The tendency of the board to bend may be
initiated if the sheets are raised off the continuous flat
supporting surface recommended for storage and leant

against a wall or laid to bridge between end supports.

Thesheets natural tendency to bend under their own
weight will be enhanced if they are stored in a damp
atmosphere where the core of the board will absorb
moisture.
It is most efficient to fix sheets with clout nails, as
their bigger head offers an improved grip on the curved
surface, which can be under some pressure. It is also
better to lay sheets so that the bend is over the longer
dimension. This will require a slight reconfiguration of
the horizontal framing members to ensure continuous
support behind joints in the boards. If done well, this
establishes a consistent curve, on which a minimum
variation in the thickness of skim coat will be necessary.

USING PLASTERBOARD
The frame may also be clad in 9mm
plasterboard sheet after wetting
with water, this will bend without
fracturing. Imperfections in the
curve may be corrected during the
application of a minimum 3mmthick skim coat of plaster.

EXPANDED METAL LATH SHEET

USING EXPANDED METAL MESH

Expanded metal lath may be
nailed or screwed to the frame
to provide a key for plaster. If
noggings are curved accurately
the lath can be fixed to them at
more frequent centres, so that
less correction is needed during
the plastering process to create
asmooth curve.

tip DISGUISING
IMPERFECTIONS
If the plaster on a curve is not convincingly smooth, then it is expedient to
eliminate any light source that washes
across its surface. The same principle
applies to uneven straight planes.
Irregularities in both are exaggerated
by elongated transverse shadows.

PLASTERBOARD WETTED,
BENT AND FIXED TO CURVE,
FINISHED WITH PLASTER
SKIM COAT

56 Alternative partitions

Freestanding walls
It is not unusual for a wall, particularly a stud partition,
unconnected to any other, to be used to subdivide an
area. This will cause no problems if it is fixed at both floor
and ceiling levels, because it can take lateral stability from
both elements. If, however, the intention is that the new
wall should not reach the ceiling, it will, even if securely
fixed to the floor, lack the stability to support additional
loadings or to withstand impact, and it will be necessary
to employ one of a number of strategies illustrated here.

Freestanding walls 57

FREESTANDING KIOSK
The rear wall of a freestanding
kiosk (left) gains stability from
its broad base, and the counter
from its L-shaped plan. The two
elements do not touch, so the
form of each is very clear and
awkward, difficult-to-construct
junctions are eliminated.

ENSURING STABILITY IN
FREESTANDING WALLS
12 Extensions at right angles to
the run of the principal wall provide
lateral bracing. Their location and
length may be varied depending
on intuitive assessment of particular
conditions. They may be shorter
and lower than the main wall, but
the longer the points of contact
and connection between the two,
the stronger the structure. If it is
important that the visual integrity
of a main wall is not compromised,
then the bracing walls may be
finished differently and the detail
of the junction treated to suggest
physical separation.

34 Angled additions also widen

the effective base.
56 Curves notionally widen the
base of the structure and adjust its
centre of gravity.

78 Lateral support can also be

derived from low-level furniture
units along all, or a significant
proportion of, the wall length.
These offer opportunities for a
wider, more substantial fixing to
the floor and a counterweight
against the tendency of the wall
to pivot around a narrow base
fixing. Detailing can make the
furniture components visually
distinct, and if they stop short
of the ends of the wall they will
read as separate elements.

910 Broadening the base of a

wall will lower its centre of gravity,
and allow more opportunities for
floor fixings. One or both vertical
sides can be angled.

58 Alternative partitions

Floating walls
Walls designed to demarcate areas may hang from the
ceiling and stop short of the floor. However, it is never
sensible to attempt this if they are to descend to a height
where people come into contact with them, because any
pressure will cause them to pivot around the fixing point
and put excessive stress on that joint.
The solution is to incorporate columns that
run between ceiling and floor or between the lower
structural member of the suspended wall and the floor,
with adequate anchorage to both. The elements of such
structures can be detailed so that the cladding sits in front
(proud) of the framing, to make the wall plane visually
dominant. It is, however, always worth considering the
value of visual separation if, once the area is inhabited by
people and furniture, the impact is lost.

Ceiling fixings
Isolated fixings between wall and ceiling can provide
adequate structural support, but this will be significantly
improved if the connecting members are treated as
columns contained within the thickness of the wall and
spanning from the floor to stable elements in or above
the ceiling. If they are attached only to the top of the

new wall their junction will be less substantial. Exposed

lengths of column can be made visually distinct from
the wall surface. They may be finished differently, and if
the face of the wall sits in front of them its top line will
remain unbroken. If they are set back from the ends of
the wall their visual impact will be further reduced.

Alternative fixings
It is often difficult to make a secure structural connection
at ceiling level. Sometimes the ceiling height may make
it impossible and sometimes the damage caused in the
construction may be unacceptable.
While fixings may be made discreetly at floor level,
there is always a danger that, when a base is too narrow,
the ratio of its width to the height of the wall will offer
little stability. Without access to ceiling support a solution
is to connect the top of the structure to an existing wall
or column, or to design the whole to allow separate
components to be connected at high level to broaden
the base of a new composite structure. This strategy is
particularly useful for exhibition structures that should
not interfere with existing permanent elements.

EXPOSED CEILING FIXINGS

EXPOSED FLOOR FIXINGS

While the partition can be securely

fixed to the floor, its height will
make it unstable and liable to
oscillate. Minimal connections
at ceiling height prevent its
overturning.

While the partition suggests that

it is floating above floor level,
the discreet fixings at floor level
prevent it from oscillating and
weakening its ceiling connection.

EXPOSED FLOOR AND CEILING

FIXINGS
A wall element can be held clear
of floor and ceiling. The fixing at
ceiling level must be to a rigid
structural element; it cannot
be supported adequately by
plasterboard, which will fracture
under impact pressure.

Floating walls 59

CEILING STRUCTURE

FLOOR AND CEILING FIXINGS

EXAMPLE OF STABILIZED STRUCTURE

A recess between wall panels and

floor or ceiling planes will help
suggest that the panel is visually
independent of both, especially if
the face of the recess is painted to
match the ceiling rather than the
floating wall.

Freestanding elements joined overhead to avoid

any risk of overturning.

PAR TIMBER FRAMING

WALL PANELLING
PAR TIMBER FRAMING

FLOOR STRUCTURE

section

plan

CROSS-BRACING

OVERHEAD STRUCTURES

OUTRIGGERS

High-level connections and cross-bracing

give a wide, stable base to two 10mm-thick
freestanding partitions (above).

The stabilizing structure overhead

accommodates existing columns while also
creating a sense of enclosure in the space
below (top right).

The principle of overhead bracing applies to

more permanent structures where walls are
connected to and take support from outrigger
columns (above). The circular element gives
extra rigidity to the comparatively fragile blue
cross-supports.

60 Alternative partitions

Base fixings for partitions

It is important to provide a secure fixing for the base
of exposed supports. Timber posts can be slotted into
pre-fabricated metal sleeves, which are welded to a base
plate that is, in turn, drilled to allow a screw fixing to
the subfloor. The plate can be covered by the floor finish,
which can be trimmed precisely around the sleeve. There
is no reason why the plate should not sit on top of the
floor finish, although if this is done it makes sense to
upgrade the quality of the plates finish, perhaps using
stainless steel, perhaps by chamfering the edges. If the

timber post is machined to fit the sleeve tightly, no

further fixing is required. The visible faces of the post
can be aligned with those of the sleeve.
Separating the sleeve from the base plate by a metal
rod, thin but strong enough to support the imposed
load, will enhance the idea that the wall is floating.
The post may be housed in a four-sided sleeve, but an
alternative, which may be slightly easier to fit on site,
is the two-sided sleeve with the post secured by a bolt or
screws. The post may then project beyond the confines
of the sleeve, enhancing the impression of floating.

PAR
TIMBER
POST

NUT

PAR
TIMBER
POST

PAR TIMBER POST

WASHER
BOLT

PAR
TIMBER
POST
PRE-FABRICATED
STEEL BASE
SHOE SCREWED
TO EXISTING
FLOOR

POST
REDUCED
TO FIT
METAL
SLEEVE
POST
REDUCED
TO FIT
METAL
SLEEVE

PRE-FABRICATED
STEEL BASE SHOE
SCREWED TO
EXISTING FLOOR

section
ALTERNATIVE FOOT FIXINGS
Timber posts may be machined
to align precisely with the faces of
the sleeve (1) or further shaped
to embellish the geometry of the
junction (2). A steel sleeve, its base
bolted to a subfloor and concealed
by the floor finish, provides a
secure fixing. Alternatively, the
fixing plate can rest directly on the
existing floor the strength of the
steel components can be exploited
to dramatize the relationship of
post to floor (3).

Cladding floating partitions 61

Cladding floating partitions

It is possible to clad floating partitions with plasterboard
sheets, but the number and vulnerability of edges
suggests that it is appropriate to use a more resilient sheet
such as 6mm plywood, MDF or even opaque, translucent
or transparent plastic. While these materials are rigid
enough to contribute to the stability and durability of
the structure, they do present problems for the filling of
joints. The inevitable movement will cause joint filler to
crack, unless it has a degree of flexibility.
A solution is to accept visible joint lines and arrange
them to make a pattern. The most critical and vulnerable
joints are those on vertical edges, and one possibility is to
make a robust, mitred joint with edges cut at 45 degrees
where they meet to avoid exposing the core of the panel
materials and to suggest a thicker, solid element. These
can be difficult to fabricate in the busy environment of
the worksite, and so shadow gaps and recessed planes are
more expedient for on-site fabrication.

CLADDING OPTIONS FOR

ISOLATED PARTITIONS
1 Planed timber framing is set back
610mm from the edge of the
cladding panel. Panel and frame
may, or may not, be painted to
read as one unit.
2 With a sheet material such as
MDF, which can be cut to give a
robust edge, a recess can be made
that avoids the need for a precise
joint between butting panels.
3 Mitred joints suggest a solid
panel, but require precise
fabrication and are probably
best constructed in a workshop.

PAR TIMBER FRAME

CLADDING PANEL

PLAN
RECESS

PAR TIMBER FRAME

CLADDING PANEL

PLAN
MITRED JOINT

PAR TIMBER FRAME

CLADDING PANEL

PLAN

62 Alternative partitions

Fixing methods
All sheet materials used as decorative finishes for
partitions will need to be attached to a supporting frame.
Some installations will require a fixing that may remain
visible as a feature of the wall; others will require a fixing
that is better concealed.
A vertical or horizontal framing member should be
located behind every joint to ensure that the faces of
adjacent panels line through and that the hollow core is
not exposed. There are two basic principles for dealing
with visible joints.

Cover strips
The traditional method is for joints to be finished
with a cover strip, which has the virtue of masking
imperfections in the construction. The strips may be
used to clamp the panels in position, in which case
the method of fixing them to the frame will be visible.
Alternatively, the primary method of fixing the panels
themselves, with nails or screws, may be hidden by the
cover strips. With this second option, the fixing of the
cover strip, either by gluing or with thin, small-headed
panel pins, may be more discreet since it supports only
its own weight. Filling the recess caused by the very small
heads of panel pins is simple and quick, and any evidence
of visible fixings will be eliminated if the strip is painted.

tip finishes for SHADOW-GAP partitions

Framing, when exposed by a shadow gap,
needs to have an acceptable quality of finish
and is often painted or stained a darker hue
to emphasize the shadow and disguise any
imperfections.

Shadow-gap solutions
A more modern solution, intended to eliminate cover
strips, exposes the joint, expressing it as a recess between
cladding materials. This shadow gap is typically about
1012mm wide and disguises slight discrepancies between
adjoining elements, but requires greater precision in its
assembly than a cover strip, particularly to ensure that
the width of the joint recess does not vary along its
length.

Fixing methods 63

CLADDING PANEL

CLS TIMBER FRAME

COVER STRIP

COVER STRIPS
The traditional method: joints are
finished with a cover strip (1,2,3).
The smooth-planed cover strip
holds the cladding sheet materials
in position and neatly masks the
comparative roughness of the
supporting framework.

SHADOW GAPS
The more modern solution,
intended to eliminate the cover
strip, exposes the joint, expressing
it as a recess between cladding
materials (4,5,6,7).

CLADDING PANEL

PAR TIMBER FRAME

RECESSED SHADOW GAP

64 Alternative partitions

Invisible fixings
It is possible to make completely invisible fixings.
Cladding elements can be fixed to studwork from behind
if this is anticipated early enough in the design phase
and an appropriate construction sequence established. It
is standard practice to use screws because the impact of
nailing would require significant counter-bracing during
assembly. It is possible to reduce the length of screw
required for rear fixing by making a recess in the framing
timber using a drill bit of a diameter big enough to
accommodate the head of the screw and the screwdriver.
It is, however, more usual to employ a metal angle, predrilled to take screws, which may therefore be shorter,
easier to fix and able to offer a more direct and robust
fixing. It is, of course, impossible to use this method on
both sides of a wall.

to wall brackets or battens. It is usually enough to hang

only from the top edge and allow gravity to hold them
in position. A gap at least 5mm greater than the overlap
of the brackets or battens must be left between the top of
the hung panel and the ceiling or horizontal surface
above it so that it can be manoeuvred over the bracket
or batten before being dropped into position. When the
panel is supported by a single top batten, vertical strips
the same width as the hanging batten will ensure that
it does not hang at an angle. If the panel is required to
float visually, the vertical battens can be excluded and
a horizontal batten the same width as the hanging batten
will maintain the vertical face and remain invisible if it
stops short of the panel edges. Any detail must ensure
that the walls untidy core is not exposed.

Demountable partitions

Timber split battens In its traditional form, the hanging

An alternative method, which is particularly useful

when it is desirable to have demountable partitions
to allow access to service ducts, is to hook panels on

mechanism described as split batten involves fixing

one section of a timber batten, cut at an angle, to the
supporting structure and the other to the back of the

PAR TIMBER FRAME

1
PLAN

2
PLAN

HOLE TO TAKE
SCREW HEAD
CLADDING
PANEL

PAR TIMBER FRAME

SCREW ENGAGING
WITH REAR OF
CLADDING PANEL

3
PAR TIMBER FRAME
ceiling

METAL ANGLE

CLADDING PANEL

PLAN

REAR-FIXING WALL PANELS

12 It can be difficult to make a

WALL PANELS WITH

CONCEALED FIXINGS

secure connection when a long

screw is inserted into a thin panel,
and it is often more effective to
drill a hole to allow the use of a
shorter, thinner screw.
3 Mild steel or aluminium angles
allow fixings to framing and panels
with short screws.

For screw fixings, rear access

will be required for installation
and subsequent access will be
impossible unless planned for.
Split bracket methods allow front
installation and easy removal,
which is particularly useful for
cladding duct spaces within walls.

ceiling

softwood head plate

Invisible fixings 65

panel. It is simple to hook the panel-mounted batten

behind that on the wall, and also possible to slide it
sideways to even out the widths of the joints. The poor
quality of much timber means it can be difficult to find a
perfectly straight length, and that the tendency to warp
can be exacerbated by the splitting process.

CEILING LEVEL

Metal split brackets Timber, partly because of poor

quality, is being replaced by a metal split bracket
alternative that offers greater precision and projects
less from the supporting structure. Where a more rigid
or permanent fixing is required, a number of hangers
may be distributed over the height of the panel, at
approximately 800mm centres, to increase contact with
the supporting frame and eliminate bowing.

CEILING LEVEL
HEIGHT OF RECESS
MUST BE X + 5MM TO
ALLOW CLEARANCE
FOR HANGING AND
REMOVAL

X+5

X+5

UPPER (HANGING)
BRACKET

HEIGHT OF RECESS
MUST BE X + 5MM TO
ALLOW CLEARANCE
FOR HANGING AND
REMOVAL

UPPER (HANGING)
BRACKET

X HEIGHT

LOWER (SUPPORTING)
BRACKET

X HEIGHT

LOWER (SUPPORTING)
BRACKET
TIMBER FRAMING

TIMBER FRAMING
CLADDING PANEL

CLADDING PANEL

section

section

TIMBER SPLIT BATTEN

METAL SPLIT BRACKET

The batten on the back of the

cladding panel is dropped behind
that attached to the wall. Since
there is no rigid fixing, horizontal
adjustment is possible.

Timber split battens are

increasingly being replaced
by metal brackets that use the
same principle. They project less
beyond the face of the supporting
wall, and are easier to fix.

VERTICAL BATTENS
It is good practice to leave a gap of
at least 10mm between adjacent
panels, since there will be some
slight variation in hanging angle
which will become obvious if they
are too close. This gap, however,
needs to be blocked with a vertical
batten to hide unfinished surfaces
behind it. The batten will also keep
the panel at a constant distance
from the supporting structure.

TIMBER FRAMING

TIMBER BATTEN TO KEEP

PANEL FACES VERTICAL

CLADDING PANEL

PLAN

66 Alternative partitions

Glazed partitions
Glass is a popular option for partitions. It conducts
light to those interior spaces without access to windows
and opens up long views across subdivided spaces. Its
shortcomings are that it must be toughened or laminated
to give it the necessary strength to resist inevitable
impacts, and it has poor fire resistance and poor soundreductive properties. These problems may be solved with
various specialist glasses and details. Manufacturers are
continually developing new products, but these, and
existing products that improve basic performance, tend to
be significantly more expensive than standard products.

Ensuring visibility
Paradoxically, clear glass partitions are used where,
ideally, a designer would have no division. They provide
the means to make a wall that effectively disappears,
but this can cause difficulties. A clear partition will
not register in peoples peripheral vision and they may
collide with it, painfully and embarrassingly. The usual
solution is to use translucent or opaque dots or stripes at

STRUCTURAL MEMBER

SILICONE BEDDING PAD (TO

CUSHION CONTACT BETWEEN
GLASS AND FRAME)

1:1

METAL ANGLE

TOUGHENED OR LAMINATED
GLASS
CEILING FINISH

SECTION

glass partition: CEILING

The glass sheet is made to
disappear into the ceiling.

14

1:1
eye level. Known as manifestation, these can be sandblasted or acid-etched into the clear glass at production
stage or applied later as adhesive film. They offer some
opportunity for decorative pattern but may underline the
element of compromise.

Invisible framing
When glass is used to minimize the presence of a
partition, it will also be desirable to minimize the visual
impact of the necessary framing. This may be achieved
successfully if the glass sheet is made to disappear into
the floor, walls and ceiling.
This is not particularly difficult to achieve, but the
glass must be installed early in the construction process
normally out of the usual operational sequence and
this is liable to complicate other work on site. While the
toughened glass necessary to meet safety requirements is
unlikely to be damaged by normal abuse, if replacement
is necessary this is liable to be complicated, involving the
removal of, and damage to, surrounding elements.

14

Glazed partitions 67

tip signalling ON
GLAZED PARTITIONS
The conventional mechanisms for preventing people colliding with fully glazed
partitions, such as a row of red dots at
eye level, are familiar and represent a
compromise to achieving the original
concept of a wholly transparent plane.
It is sensible to accept and exploit the
need for a warning device and to add
a more considered pattern, whether
sand-blasted or laser-cut adhesive
plastic sheets. Occupants of rooms
behind glass walls may also welcome
the increased privacy that results.

TOUGHENED OR LAMINATED
GLASS

METAL ANGLE
SILICONE BEDDING PAD (TO
CUSHION CONTACT BETWEEN
GLASS AND FRAME)
FLOOR FINISH

Glass partition: floor

15

SECTION

The glass sheet is made to

disappear into the floor.

68 Alternative partitions

Frames for glazed partitions

PAR TIMBER GLAZING BEAD

PAR TIMBER FRAMING

SILICONE BEDDING PAD

TOUGHENED OR
LAMINATED GLASS

If the designer is not committed to making a partition

that is near-invisible, an opportunity arises to make
creative use of the framing pattern. Such a frame is
generally easy to construct as it is not required to keep out
the weather and so does not require the mouldings and
chamferings used to cast water off external frames. The
cross-section can be as simple or as complex as desired.
The reduction in glass panel size offered by framing
can improve the fire-resistance qualities of the partition,
reducing the specification and cost of the glass used. It is
conventional, and therefore economical, to run framing
members horizontally and vertically. Where appropriate,
however, it is comparatively simple to make an irregular
or angled pattern.

Framing materials
The most frequently used framing materials are
hardwood, usually stained to exploit colour and grain,
and softwood, stained or painted. Metal framing is
equally effective, allows a smaller section and may be
justified if it is necessary to match the aesthetic intention
of the interior as a whole.
Whether using wood or metal, it is good practice to
use a soft, resilient strip between glass and frame, to allow
a slight degree of flexibility that will reduce the chances
of the glass cracking when movement occurs. It was
traditional to use thin lengths of leather, but now rubber
or silicone strips, often with adhesive edges, are standard.
They have very little visual impact.

Off-the-shelf systems

STANDARD WOOD FRAMING

Sections of softwood or hardwood
framing can be kept very simple
since they do not deal with wind
and rain. It is good practice,
however, to slightly round the
sharp angles, particularly in
softwood frames, to minimize
localized impact damage.

There are metal framing systems, usually aluminium,

that may be bought off the shelf and, like all proprietary
products, impose some restrictions. However, if these
are assimilated early in the design process they may be
used positively. Such systems tend to provide a framing
member with a comparatively large but very simple
cross-section. The methods for fixing such frames to
supporting elements and holding the glass in position are
complicated and comparatively crude, but are concealed
by cleaner clip-on casings. More robust and rigid standard
sections can reduce bulk. These usually have visible
screw or nut-and-bolt fixings, and consequently a more
industrial appearance.

Curved glass
RECESSED TIMBER BASE

SECTION

It is difficult, and therefore expensive, to curve glass, so

it is more normal to translate the curve into a series of
facets. The idea of the curve can be reasserted by curving
horizontal framing members.

Frames for glazed partitions 69

TOUGHENED OR LAMINATED
GLASS

MILD STEEL ANGLE BEAD

SCREW (FIXED IN PRE-DRILLED
THREADED HOLE)
METAL GLAZING BAR
MILD STEEL ANGLE BEAD
SILICONE BEDDING (TO CUSHION
CONTACT BETWEEN GLASS AND
FRAME)

PLASTIC OR TIMBER BEDDING

BLOCK (TO CUSHION CONTACT
BETWEEN GLASS AND FRAME)

tip creating a glass curve

SECTION

STANDARD METAL FRAMING

Emphasizing horizontal elements in a glass

curved wall expresses the implied geometry
more clearly. Vertical members interrupt the
flow of the curve.

Simple metal sections can be

aggregated to form a suitable
framing system.

HORIZONTAL
FRAMING

70 Alternative partitions

Framing and beading

The relative configurations of the frame and the bead that
hold the glass in place are crucial in determining how the
pattern of a window or glazed screen is perceived. It is, as
in any joinery, unwise to line the faces of frame and bead
through, as there will inevitably be a minor misalignment
apparent to the observer, especially one who is in regular
close contact with the element.

The solution is to set the face of one of the

elements back from the other, or to introduce a shadow
gap between two nominally aligned faces. In timber
construction, corners are usually mitred for visual
continuity of the component, and beads are fixed with
panel pins, screws or glue.

GLASS

GLASS

TIMBER
GLAZING BEAD

TIMBER
GLAZING BEAD
TIMBER FRAME

PLAN
TIMBER FRAME
WALL

SECTION
FRAME WITH PROJECTING
BEADS
The beads project and the frame
recedes visually.

GLASS

GLASS

TIMBER
GLAZING BEAD

TIMBER GLAZING BEAD

TIMBER FRAME

PLAN
TIMBER FRAME
WALL

SECTION

FRAME WITH BEADS SET BACK

The frame dominates because the
glazing beads are set back.

Framing and beading 71

GLASS

GLASS

TIMBER
GLAZING BEAD

TIMBER GLAZING BEAD

TIMBER FRAME

PLAN
TIMBER FRAME
WALL

SECTION

FRAME WITH RECESS

Frame and beads appear to be in
the same plane. The recess visually
separates them, masking minor
misalignments on their faces.

PLASTERBOARD/
PLASTERBOARD + SKIM
CLS STUD FRAMING

CLS STUD FRAMING

GLASS

TIMBER GLAZING BEAD

GLASS

TIMBER GLAZING BEAD

WALL
PLASTERBOARD/
PLASTERBOARD + SKIM

SECTION

HIDDEN FRAME
The glass disappears into the wall.
This option requires that the glass
is inserted before the finishing of
wall surfaces is completed, which
may cause some complications

during construction and more

extensive work if replacement is
necessary. Skim plaster should
be finished against an expanded
metal bead.

PLAN

72 Alternative partitions

Joining glass sheets

Glass sheets must be pre-drilled to accommodate
the screws and bolts. Holes should be larger than
the diameter of the screw or bolt, to allow for minor
adjustment on site and to absorb movement. Metal or
rubber washers should be an integral part of the element
in order to cover the larger hole.

The overall size of glass sheet that may be used in a

project depends on the dimensions of the doors, and
sometimes stairs, that give access to a site. It is usually
possible, except with tight stair or corridor access, to use
a single sheet of glass that can span the conventional,
modern floor-to-ceiling height of 2400mm.
It is possible to make fairly innocuous joints to
seal the junctions of glass sheets using a clear silicone
strip, but these are, nevertheless, visible and represent
a compromise in the creation of an invisible partition.
Large glass panels have significant inherent strength, and
while it is possible to join them with modern specialist
adhesives, metal connectors remain more usual.

Flat clamps Jointing elements can be flat clamps, which

may be standard, mass-produced items or designed
to meet project-specific aesthetic criteria. All need to
conform to basic principles of pre-drilled holes, for onsite adjustment, and resilient washers, to allow joints
to be tightened without cracking the glass.

Metal connectors

Metal finger joints and glass fins Three-dimensional

In tall spaces it is often necessary to make both horizontal

and vertical joints, and these must be structurally stable
as they are unconnected to floors, walls or ceilings.
Stainless steel is most often used because of its strength
and appearance. There are a number of manufactured
jointing elements that will provide the necessary
structural integrity.

finger joints give a degree of depth that helps brace the

glass against impact along its length. This bracing can be
increased if the projecting fingers are connected vertically
to create a single bracing element. An alternative to using
a metal connecting piece for this is the glass fin, fixed
to the wall sheets by metal clamps or by the specialist
adhesives that are increasingly used in glass structures.
FLAT CLAMPS
12 A flat plate, to which the

METAL FINGER JOINTS

34 Steel or aluminium finger

corners of four sheets of glass

are bolted, provides structural
continuity. Joints may be sealed
with translucent silicone filler.

units provide rigid connection

between sheets of glass. The
projection of the finger unit at
right angles to the plane of the
glass also gives lateral bracing.

GLASS WALL
PANEL

ELEVATION

PLAN

FLAT METAL
PLATE

SILICONE
WASHER

PROPRIETARY METAL
CONNECTOR

2 or 4 way connector

SILICONE
WASHER
GLASS WALL
PANEL

ELEVATION

PLAN

2 or 4 way connector

Joining glass sheets 73

Lateral bracing
When a number of glass panels are connected in both
their vertical and horizontal planes, the wall created
will require lateral bracing to stiffen the joints against
pressures exerted on its face. Vertical or horizontal fins,
or both, fixed at right angles will provide a continuous
connecting member between glazed panels, and a rigid
skeleton that increases the effective structural depth of

the wall plane and its resistance to lateral forces.

The fin can be a solid strip of metal, although this
may be deemed visually obtrusive. The mass of metal may
be reduced by cutting out areas that have no structural
role, but the more common alternative is to substitute a
fin of toughened glass, which can easily meet structural
obligations with a minimal visual presence.

FIN FIXINGS
1 An adaptation of the finger
joint connects a glass fin to the
wall panels.
23 Flat plates connect two fins
both vertically and horizontally
to the wall panels.

STRUCTURAL GLASS FIN

METAL CONNECTOR UNIT
SILICONE JOINT
SEAL
SILICONE WASHER

GLASS WALL
PANEL

1
SECTION

LATERAL BRACING
45 Toughened glass can have
significant structural strength
and when used as a vertical
or horizontal fin can provide
lateral bracing.

TOUGHENED GLASS FIN

METAL SPLICE PLATE

SILICONE BUTT
JOINT

STAINLESS STEEL
PLANAR JOINT

ELEVATION

TOUGHENED GLASS
PANEL
SILICONE WASHER

SILICONE BUTT
JOINT
STAINLESS STEEL
PLANAR BOLT
TOUGHENED FIN

PLAN

CHAPTER 4 DOORS

076 BASIC PRINCIPLES

078 MODERN DETAILING FOR DOORS
080 SLIDING DOORS
082 FANLIGHTS
083 GLASS IN DOORS
084 NON-STANDARD DOORS
085 FIRE REGULATIONS FOR DOORS

76 Doors

Basic principles
Doors manufactured for interiors are not required to cope
with weather. Consequently, there is considerable freedom
in the construction of the opening panels (or leaves)
and the frames that trim wall openings and carry the
hinges on which the leaves pivot. Essential principles of
installation remain important as the opening and shutting
of door-leaves subjects adjacent finishes to continuous
impact. If these principles are understood, there is scope
for creative variations on standard solutions.

Standard materials and sizing

While leaves and frames may be manufactured from
metals and plastics, timber remains the most common
material. Hardwoods are favoured for the decorative
qualities of their grains, while softwoods are usually
painted. Leaves are seldom manufactured specifically for
a project unless a significant aesthetic gesture is sought;
they are almost invariably specified from the wide range
of options offered by specialist manufacturers. Doors
may be heavy, with solid timber leaves and frame, or
extremely light, with leaves made from a hollow core
of honeycomb cardboard between two skins of 3mm
plywood or hardboard, glued to a perimeter structure
of 27 x 19mm softwood. Standard frame sections are
also manufactured, and save construction time.
The core construction of leaves is often determined
by their role as fire-resistant elements. Any upgrading
can significantly increase their weight and thus influence
decisions about frames and the type and number of
hinges, and perhaps about the construction of supporting
walls. The core construction of a wall, whether masonry
or stud-framed, is comparatively crude, and openings
for doors reflect this. The basic opening, with widths of
700, 800 and 900mm and heights of 2000 or 2100mm, is
usually referred to as the structural opening. The more
precise, factory-made dimensions of standard frames and
door leaves are designed to fine-tune these raw openings.
Leaves are typically 526, 626, 726 and 926mm wide and
1981 or 2040mm high, and, with frame widths of 32mm,
fill basic openings with a clearance of 2mm to allow
opening and shutting. Internal leaves are 35 and 40mm
thick (the former is more common). Internal fire doors
are 44mm thick.

Door construction
Jambs and heads The word jamb refers to vertical
framing on each side of a door and head to the
horizontal framing on its upper edge. Both have the
same section. Normally they are timber, which is easily
adapted on site, but since dimensions for door frames are

standardized, metal and plastic are viable particularly in

large, repetitive installations. The jambs role is to make
a robust junction between the wall and the door opening,
and to support the leaf.
Both the jambs and head are nailed or (particularly
for metal studwork) screwed (often through wooden
packing pieces that fill gaps between components) into
the faces of the raw door opening. When a concrete lintel
is used in masonry construction, it is sufficient to nail or
screw the head to the vertical jambs. The frame should
project far enough beyond the faces of the unfinished
wall to align with the face of the finishing material, to
facilitate the fixing of architraves. For example, it should
project 13mm for plasterboard and skim.

Architraves The junction between frame and wall finish

is most vulnerable to cracking; the traditional solution is
to mask it with a cover strip: the architrave. This is the
most common and reliable solution and, while elaborate
carved examples have largely disappeared, modestly sized
and moulded strips deal with the problem effectively.
It is possible to fix the architrave to the frame
directly, though it is better practice to insert a 13mm
treated softwood ground as a buffer to absorb hammer
impact and to nail through or into. Fixing with screws
or glue will not cause impact damage but the recesses of
screw heads will require more filling before painting.
Junctions of vertical jamb and horizontal head
architraves should be cut with 45-degree mitres so that
the lines of mouldings, no matter how simple, continue
unbroken and no end grain is exposed. Architraves are
normally carried to the floor and provide a face against
which the sawn end of a skirting may be finished. For
that reason, skirtings should not be any wider.

Fixing architraves It is possible to fix the architrave

through the plasterboard into the final length of the stud
frame, but it is better practice to insert a 13mm treated
softwood ground as a buffer to absorb hammer impact
and to nail through or into it. Fixing with screws or glue
will not cause impact damage, but the recesses of screw
heads will require more filling before painting. Given
advances in adhesive quality, architraves are often glued
in position. However, with uneven existing surfaces, it
is sensible to use a nail or screw fixing. With these, the
heads should be sunk below the surface of the moulding
and the shallow indentation filled, sanded and painted.
Stops The stop is the element of frame against which
a door closes. It need not be continuous around the

Basic principles 77

opening, but usually is, for visual coherence and the

reduction of draughts or noise. It may be nailed, screwed
or glued to the main frame element, although these
options may be governed by fire regulations. For high
performance, the frame and stop should be cut from a
single piece of wood, which is the more expensive option,
and wasteful of timber. The stop should be set back by the
width of the door leaf from the face of the frame, so that
frame and door face line through on the side that the
door opens.

Traditional door-FRAME
construction
The architrave covers the joint
between plaster and frame, which
is liable to crack and fracture, and
provides a vertical face against
which the skirting is finished. The
batten provides a solid connection
between architrave and stud
frame, and protects the plaster
during nailing.

Hinges
Hinges are also standard components, but it is important
to specify type and number. Heavy doors, with extensive
glazing or a high fire resistance, will require more than
the normal pair of hinges. Some doors, again often for
reasons of fire resistance, will need to be self-closing and
some hinges can meet this requirement, either operating
by gravity or springs. They may not have the strength of a
conventional wall-mounted door closer but, if regulations
permit their use, they are more discreet.

STUD PARTITION FRAMING

3MM PLASTER SKIM COAT
9.5MM PLASTERBOARD
STUD PARTITION FRAMING

TIMBER BATTEN
PAR TIMBER SKIRTING

PAR TIMBER SKIRTING

3MM PLASTER SKIM COAT
9.5MM PLASTERBOARD
PAR TIMBER ARCHITRAVE
TIMBER GROUND
PAR TIMBER STOP BEAD
STUD PARTITION FRAMING
PAR TIMBER JAMB (OR HEAD)
TIMBER PACKING PIECE

PLAN

DOOR LEAF

78 Doors

Modern detailing for doors

While the timber members of a door frame are
comparatively robust, wall surfaces, typically finished in
plaster or plasterboard, are more vulnerable. It is standard
practice, therefore, to use proprietary metal plaster stops
and beads to provide a protective edge to plaster surfaces
or to create a shadow gap.
The shadow-gap option omits architraves, creating
a separation between frame and wall that eliminates the
possibility of cracks or minor misalignments. It enhances
the perception of the wall as the dominant visual element
and the door as a secondary insertion. There are two basic
configurations: the front edges of the frame may align,
or appear to do so, with the faces of the finished walls; or
the frame may sit back within the thickness of the wall,
further emphasizing the latters visual dominance.

Preventing problems
The shadow gap poses problems with fragile exposed edges
of plaster or plasterboard surfaces and junctions of skirtings
and frames. They may be strengthened with expanded
metal beads for plaster finishes, or metal reinforcement
strips for drywall construction. When the dimensions of
proprietary beads are considered at the start of the process,
neat alignments are feasible, but it is difficult, and therefore
expensive, to achieve the precision that the minimalist
aesthetic requires. If skirting boards finish against frames,
exposed timber end grains are avoided.
A range of expanded metal plaster stops offers detailing
options, and may be used with 13mm three-coat or 3mm
skim-coat finishes. They are a dull grey in their natural state,
but can be painted to match adjacent surfaces.

SKIRTING BELOW
DOOR LEAF
CLS STUD FRAME
PLANED TIMBER
SUBFRAME
PLANED TIMBER
DOOR STOP
TIMBER PACKING PIECE
PLANED TIMBER DOOR
FRAME
PLASTERBOARD AND SKIM

PLAN

TIMBER CORNER BEAD

CORNER BEAD
PLANED TIMBER DOOR
FRAME
PLANED SUBFRAME
PLANED TIMBER DOOR STOP
NAILED OR SCREWED
TO FRAME
SAWN TIMBER PACKING
PIECE
DOOR LEAF
PLASTERBOARD AND SKIM

PLAN
SHADOW-GAP FRAME
1 A frame with a width that

corresponds to that of the wall

can be given visual independence
with a timber ground that makes
a shadow gap between the frame
and wall.

2 A door with no fire-resistance

obligations can sit back within the
width of a standard wall thickness.
The frame can be fixed directly to
the structure of the wall, but the
ground creates a shadow gap that
visually separates wall and frame.

Modern detailing for doors 79

LINE OF SKIRTING
BELOW
PLASTER SKIM COAT
PLASTERBOARD
PROPRIETARY EXPANDED METAL
PLASTER STOP
PLANED TIMBER FRAME
SAWN TIMBER PACKING PIECE
STUD PARTITION
PLANED TIMBER
SKIRTING BELOW
PLASTERBOARD
PLASTER SKIM COAT

PLAN

LINE OF SKIRTING
BELOW
PLASTER SKIM COAT
PLASTERBOARD
PROPRIETARY EXPANDED METAL
PLASTER STOP
PLANED TIMBER FRAME
STUD PARTITION
SAWN TIMBER PACKING PIECE
PLANED TIMBER
SKIRTING BELOW
PLASTERBOARD
PLASTER SKIM COAT

PLAN

Expanded metal plaster

stopS
3 The expanded metal plaster

4 If grooves are made in the

frame to accommodate the
expanded metal plaster stop, the
resulting detail will better avoid
misalignment and make it easier
to leave the frame unpainted while
painting the stop and wall.

stop provides a straight line

against which a plaster skim
coat can be precisely finished
and a ready-made shadow gap
that, when painted, is visually
indistinguishable from the painted
plaster and frame. The point
where it touches the frame will,
however, be likely to show as a
light line. Itwill also be difficult to
line through the edge of the stop
andthe frame exactly.

tip ARCHITRAVES
Plaster stops and beads offer accurate
edges, but their very precision means
that they may not sit satisfactorily with
the imprecision of existing construction.
In the typically unsympathetic conditions
on site, there are difficulties in making
satisfactory junctions using what are
comparatively inflexible metal strips.
The traditional architrave, which evolved
to deal with areas of construction that
are vulnerable and difficult to finish to
a high standard, is worth considering
for all such locations.

80 Doors

Sliding doors
These are a useful means to open up or combine spaces,
but should look equally good open or closed and can be
perceived as an integral part of the adjacent walls.

EXISTING STRUCTURE

Sliding mechanisms

VERTICAL TIMBER
FRAMING

A wide range of products is offered by specialist

manufacturers and the priority is to integrate generic
pieces discreetly into the building fabric. Some are
designed to be visible but it is usual to incorporate them,
when open, in the depth of the supporting wall, increasing
its width if necessary. The structure and fixing of the
sliding mechanism should be robust enough to support the
weight of the door glazed doors are particularly heavy.

Recesses
The construction added to mask an overhead sliding
mechanism can be extended down the face of the wall
to create a recess in which the door locates when it is
open (see diagrams 1 and 2, opposite). Alternatively, a
slot to house the open door leaf may be created. Again,
this simply requires reinterpretation of stud-partition
principles, to create two parallel frames. There are other
manufactured solutions that confine the overall wall
width to the standard 100/120mm dimensions, and others
for curved doors in curved partitions.

Floor channels
Sliding doors must be stabilized at floor level by a guide
peg or wheel running in a floor channel. Channels,
however, create practical problems by collecting dirt, and
aesthetic concerns when a metal channel is incompatible
with the floor finish. Visual impact may be minimized
by inserting a metal channel in the base of the door and
a floor pin with which the channel will engage. The
door overlaps and conceals the pin in both the open and
closed positions (see diagrams 1 and 2). If the doors are
heavy, it may be sensible to provide wheels in the lower
edge to transfer loading to the floor. These can also act as
guides if they are set within a floor recess, which need not
be more than a few millimetres deep, as the doors weight
will reduce the tendency to swing.

Sound insulation
Sliding doors need clearance on all sides to run easily,
which creates soundproofing problems. Required standards
will probably not be met by conventional components,
but sound transference can be reduced by integrated
pneumatic buffers, which inflate to seal gaps.

TIMBER FRAMING

PLASTERBOARD AND
SKIM

EXPANDED METAL
ANGLE BEAD AND STOP
DOOR LEAF

HEAD OF SLIDING DOOR

SECTION

Some proprietary sliding-door

mechanisms are designed to
remain visible, but more utilitarian
models may be specified when the
intention is to build a structure out
from the existing wall to form a
recess to house the door head.
EXISTING STRUCTURE
SCRIM TAPE

HORIZONTAL TIMBER
FRAMING
PLASTERBOARD AND
SKIM

VERTICAL TIMBER
FRAMING
DOOR LEAF
EXPANDED METAL
ANGLE BEAD AND STOP

CONSTRUCTION OF RECESS
FOR SLIDING DOOR
With conventional stud framing,
creating a wall recess involves
construction of two independent
skins and widening of the wall from
a minimum of 100mm to at least
175mm. Where increased width is
unacceptable, a proprietary, metalframed pocket construction will
maintain a 100mm overall width.

PLAN

Sliding doors 81

Folding sliding doors

POTENTIAL STORAGE SPACE

FOLDED

PLAN

FOLDING SLIDING DOORS

A wall widened to house sliding
door panels creates opportunities
for storage (left). Hinged panels
close the recess when the doors
are extended (right).

STABILIZING SLIDING DOORS

1 The bottom of the door leaf may
be stabilized by a wheel or guide
pin running in a channel cut into
the floor. This method is preferable
for heavy doors.
2 A channel set into the lower
edge of the door leaf runs over a
pin fixed to the floor and located
so that it engages with the channel
in the open and shut positions.

OPEN

PLAN

It is not unusual to have multiple sliding doors, usually

relying on sliding or folding mechanisms, to subdivide
large spaces. It is prudent to research proprietary solutions
and to accommodate their practical requirements at the
beginning of the design process. The basic principles are
the same as for single panels but, because of their size,
their subdivision and detailing will inevitably have a
significant influence on the detailing of other elements.
It is important to consider how the opened door
panels may be integrated into the fabric of the space.
This normally involves the thickening of walls or the
introduction of storage recesses, on either the same or
the reverse side of the door recess, and requires planning
rather than detailing ingenuity since the principles of the
wall construction will be conventional.

82 Doors

CEILING
PLANED TIMBER HEAD FRAME
PLANED TIMBER GLAZING BEAD
GLASS

PLANED TIMBER TRANSOM

PLANED TIMBER DOOR STOP

DOOR LEAF

Fanlights
DOOR WITH FANLIGHT
The frame continues to ceiling
height, with a recess all round to
disguise uneven wall and ceiling
finishes. The intermediate frame is
inserted to respond to a standard
door leaf height. The area above
the door is glazed conventionally.
However, if the door is fire-rated
then the glass will have to achieve
the required rating. In most
projects this will involve the use
of wired glass.

SECTION

The most common variant on the standard door is that

with a window, or fanlight, above it. This is such a
commonly used option that it has become a standard
item in most door manufacturers catalogues, to fit the
most common floor-to-ceiling heights of 2300mm and
2400mm found in most newly built interiors. It may,
however, be necessary to produce one-off specials to fit
the non-standard dimensions of existing buildings.
The fanlight offers a way of carrying a limited
amount of borrowed light from rooms to corridors that
are situated in the middle of a floor, as well as visually
extending the door element from floor to ceiling. The
principle is simple. The side frame extends to the full
height of the room with an intermediate head frame to
receive the top of a standard door leaf and support the
fixed pane above it. Stops and glazing beads are applied
using standard techniques and fixings.

Glass in doors 83

Glass in doors

Vision panels

The area of glass in a door can vary from small vision

panels to an entire single sheet of glass. All glass used
must be strong enough to withstand not only fire but the
impact caused by vigorous use. In all but the very smallest
panels it will be necessary to use reinforced glass.

Wired glass
The most common and economical reinforcement is
wired glass, clear or translucent, with a usually square
wire mesh embedded in its core. The fine mesh holds
the glass together if it cracks as the result of impact or
fire, meeting approved standards. A common aesthetic
problem with wired glass is that the geometry of the core
mesh is not necessarily perfectly square, so lines on the
edge will not be parallel to the framing.

WALL

FLOOR SPRING

DOOR LEAF

PLAN

These are often a practical requirement (preventing

collisions in busy areas) or a safety requirement (allowing
the inhabitants of rooms to be aware of events beyond
their walls a requirement in fire-escape provision).
Clear or translucent, toughened, fire-resistant glass meets
practical performance standards but is more expensive
than wired glass.

Unframed glass doors

It is possible to use an unframed glass panel as a door
leaf, avoiding supporting framing and stops by hinging
the panel on its top and bottom edges. This solution
cannot meet fire-resistance requirements and the glass
panel will be expensive, but the principal problem is
likely to be that of housing the floor- and ceiling-level
hinges. Timber structures are unlikely to provide robust
fixing points, and it may be impossible to cut sufficiently
into concrete floors and ceilings to make a satisfactory
connection. Appropriate hinges are standard products
from specialist manufacturers, often with springs to
hold door leaves in the closed and open positions. The
designers responsibility is to detail the work necessary
for their installation. It is always prudent to consult the
supplier for advice on specific installations.

Doors in glazed screens

When a wall or a substantial floor-to-ceiling wall section
is glazed, it is generally referred to as a glazed screen. It
will often include a door, probably glazed but sometimes
solid. It is normal practice for such large screens to be
manufactured in sections off site, in a joinery workshop
with specialist machinery, to ensure a more accurate and
soundly constructed product. The door itself may be a
standard off-the-shelf product. The complete element will
then be assembled on site.
WALL

DOOR LEAF
FLOOR SPRING

PLAN

UNFRAMED GLASS DOOR WITH

Pivot hinges recessed into
floor and ceiling planes
A door with pivot hinges on its top
and bottom edges does not need
frames, and when open allows
walls to read as unbroken planes.

VISION PANELS
An approved window to an escape
stair in a public building, using
wired glass.

84 Doors

Non-standard doors
Non-standard-sized doors need to be made in specialist
workshops. All doors experience significant internal
tensions: being asymmetrically hung, comparatively thin
and effectively two-dimensional, they have a tendency to
warp along their length. To counter this, which becomes
more critical as doors get bigger, timber must be well
seasoned and joints precisely made and glued.

Tall doors
With tall doors, which can stretch from floor to ceiling,
the door leaf is often kept narrow to accentuate its
relative height. Since larger doors are liable to be heavier
and more likely to warp, it is normal practice to use three
hinges instead of two.
Since a floor-to-ceiling door is used to minimize the
separation implied by a conventional door opening, it is
often considered desirable to eliminate the door frame.
This can be achieved by floor- and ceiling-level hinges
connected to the top and bottom edges of the door leaf;
when fully opened, these will set a leaf further out from

the face of the wall. Stops can be built discreetly into the
ceiling or wall so that they appear to be integral to those
elements rather than part of the door installation.

Fixed panels
Where the primary concern is for a visual floor-to-ceiling
element, the section of wall above the door head may be
omitted and a thinner fixed panel, typically a composite
timber board or glazed panel, inserted to extend the door
recess to the ceiling. The framing of the door can be
extended to incorporate the upper panels.

Wide doors
If a door is particularly wide it is often expedient to add a
small wheel or ball castor close to its opening edge, near
the unsupported end. Either may be discreetly housed in
the width of the bottom rail of the leaf. The continuous
action of these can wear a visible trail in the floor and,
with heavy doors, it is not uncommon to insert a metal
track, usually brass, in or on the floor surface.

CEILING

B
A

PLANED TIMBER
FRAME

RUBBER OR
SILICONE BUFFER
REBATED LEAVES
TO CREATE STOP

PLANED
TIMBER
FRAME

PLAN BB

SECTION AA

FRAMED DOOR WITH PANEL

TALL FRAMELESS DOORS

The jambs stretch from floor

to ceiling. The door leaf can
be split with a rebated stop at
conventional door-head height.

The door leaf sits within a wall

recess. The section through the
head will match that of the sides.
Additional timber framing carries
a rubber or silicone buffer that
protects plasterwork. Conventional
side hinges may be replaced by
floor- and ceiling-mounted pivots
to leave plaster surfaces unbroken.

Fire regulations for doors 85

Fire regulations for doors

One of the most important considerations in designing or
specifying doors is meeting the requirements of relevant
fire regulations. These lay down minimum periods for
which door leaves, and their frames, should be able to
withstand fire and contain flames and smoke within
the area of an outbreak. The period of resistance varies
according to the activities contained within the room and
its relationship to the recognized escape route, which is a
designated path protected by walls and door construction
from fire and smoke leading directly to the exterior.

Door leaves The most common periods of resistance

specified are half an hour and an hour. Door leaves are
manufactured to meet these levels and more. Resistance
depends on the composition of the doors core. For a
designer, it is normally a matter of specifying levels
of resistance, as most door leaves are mass-produced.
Regulations also require that some doors leading to
escape routes have vision panels. While it is possible to
design a one-off fire-rated door, the process is complex,
and it may be difficult to justify the cost of time in design

and manufacture. If attempted, then close liaison with

the fire officer responsible for final approval is vital
throughout production.

Door frames These may be bought to meet minimum

fire regulation requirements, but since these are less
complex than for door leaves it is possible to experiment
more freely with form. The most significant criterion
is that frames should meet minimum dimensional
standards, relating primarily to the thickness of door
leaves. While frames must normally be cut from solid
timber, there is a concession that the stop on a frame
providing half an hours fire resistance can be a separate
piece, if fixed with screws.
Frameless doors Where frameless doors have to meet
a fire-resistance standard, this can be achieved by the
insertion of intumescent strips into the edges of the leaf.
Heat from a fire will cause these to expand and fill gaps
between leaf and frame to prevent the passage of smoke
and flames.

One-hour door AND frame

Half-an-hour door AND

frame

The frame must be cut from one

single piece of timber.

Components of the frame may be

planted or screwed together.

DOOR STOP
DOOR LEAF

DOOR LEAF

FRAME

FRAME

PLAN

PLAN

tip Being discreet: DOUBLE Doors

Rebated meeting edges allow one half of a
frameless double door, when locked shut, to
act as a stop for the other half. An intumescent
strip, which expands when exposed to heat,
incorporated into a groove in the edge of
the door leaf will ensure that necessary fire
regulations are met.

PLAN

REBATED EDGES

PLAN

REBATED EDGES WITH INTUMESCENT STRIP

CHAPTER 5 FLOORS

088 SOLID GROUND FLOORS

090 SUSPENDED GROUND FLOORS
091 UPPER FLOORS
092 TIMBER JOISTS
094 TIMBER ROT
095 TIMBER FLOOR STRUCTURE
096 STEEL BEAMS
098 PLANNING NEW STRUCTURES
100 INSTALLING NEW FLOOR LEVELS
102 RAISING THE FLOOR
104 OPENINGS IN FLOORS
106 FLOOR FINISHES
108 FINISHING MATERIALS
110 OTHER CONSIDERATIONS

88 Floors

Solid ground floors

Solid ground floors are laid directly on to the earth.
Theearliest and simplest version of these merely
involved compacting of the earth, with excavation or
filling to create a solid, broadly level surface. This was
very vulnerable to wear, which persistently created dust.
Its durability was improved by the addition of a more
processed finishing layer often of brick, tile or wood
although the last of these was vulnerable to any moisture
that penetrated the earthen subfloor.
More recent solid ground floors have used poured
wet concrete, which is easy to level, to create a durable
surface. Standard construction involves the removal of
topsoil (because it contains organic matter), to reach
the inert subsoil stratum. The site level is made up with
loose stones, known as hardcore, over which is poured
approximately 100150mm of oversite concrete, which
contains comparatively large stone aggregate. The top
layer is a smoother 50mm of finer concrete or screed,
which can be used as a base for the final floor finish or
polished to perform as a finished surface in its own right.

Damp-proof membranes
The gradual penetration of damp through the porous
concrete is the greatest problem with any solid ground
floor. The intention must be to create a waterproof
barrierto hold back the moisture that will damage
most interior finishes.
It is now accepted practice to incorporate within
the poured concrete a damp-proof membrane (or DPM),
an impervious layer that prevents rising moisture
penetrating the fabric of the building. This is either laid
as a plastic sheet over the subfloor, alongside insulation
material, or painted on to it. The 50mm-deep fine
concrete screed is poured on to the DPM and vibrated
mechanically to produce a smooth surface to receive a
range of flooring materials. Increasingly, plastic piping
for underfloor heating is being incorporated into screeds.
The standard specification has been for 100mm screeds,
but recently this has been reduced to 50mm, which
allows faster heating of the slab. This can be problematic,
however, since the pipes can encourage cracking of
the shallow screed if the mix or drying process are not
perfectly controlled.

Repairs to poured concrete It is important when making

any changes to an interior not to damage the damp-proof
membrane. While it is possible to make an impervious
repair to a damaged membrane, the process is messy,

involving significant cutting back and making good of

both the membrane and the concrete floor. Sometimes
damage is unavoidable, as when new columns are
inserted to support additional upper levels.
The particular problem with such remedial work
is that shortcomings in the difficult repair work often
do not become apparent until enough time has elapsed
for moisture to penetrate the joints of old and new
membrane sections. Given the speed with which most
interior work is carried out, new finishes may have been
installed, and damaged, before evidence of faults appears.

Installing new damp-proof membranes When an

older floor does not have a damp-proof membrane it is
worth trying, and sometimes possible, to lay a membrane
directly on top of the existing top surface and underneath
the new finish. This strategy may determine the choice
of floor finish. A thin, interlocking engineered board,
which can be laid loose, is particularly suitable. It is
important to turn the new membrane as far up the wall
as possible, behind a skirting or wall finish, and it should
ideally be bonded to the damp-proof course within the
wall to create an unbroken barrier against all moisture
penetration.

Damp-proof courses
The damp-proof membrane is generally joined to a dampproof course (or DPC), another impervious membrane
built horizontally into one course of brickwork or
blockwork of the external and internal walls, at least
150mm above exterior ground level, to prevent moisture
rising vertically through them.
Without an efficient damp-proof course, moisture
can rise through the fabric of the walls and degrade wall
finishes. The connection between this and the floor
membrane is critical in maintaining a complete seal. If a
damp-proof membrane has not been installed, then it is
also unlikely that there will be a damp-proof course.

Injecting into masonry Where no damp-proof course

exists it is possible to inject a fluid into all masonry
walls that will make them impervious. Such work,
which involves the boring of small holes about 5mm in
diameter into the wall to ensure penetration of fluid to
its core, is normally carried out by specialists. It is worth
seeking advice from a number of specialist companies
before undertaking any damp-proofing work.

Solid ground floors 89

AVOIDING DAMP IN FLOORS

AND WALLS
The creation of a cavity within
the width of an external wall
has become common practice,
and ensures that any moisture
that penetrates the external skin
runs down its inside face and is
expelled through apertures, or
weep holes, near ground level.
In the case of brickwork these are
vertical joints left free of mortar.
It is important that this ejection
route is maintained if the level
of exterior finish is allowed to
rise above the internal floor level,
water will be retained in the cavity
and will breach the damp-proof
membrane. A level 50mm concrete
screed will normally be laid on top
of 100mm of oversite concrete,
with the membrane between
them. It is essential that moisture
from below the floor slab should
not be allowed to rise through the
inner wall skin. This is prevented
by sealing the connection between
floor and wall membranes.

OUTER BRICK SKIN

CAVITY
DAMP-PROOF COURSE (MINIMUM
150MM ABOVE GROUND LEVEL)
INNER BRICK SKIN

CONCRETE BACKFILL (TO PREVENT

WATER COLLECTING IN CAVITY)
DAMP-PROOF MEMBRANE
FLOOR FINISH
50MM CONCRETE SCREED

150MM OVERSITE CONCRETE

HARDCORE (MINIMUM 150MM

OF RUBBLE TO EVEN OUT
GROUND LEVELS)

SECTION

90 Floors

Suspended ground floors

Suspended ground floors offer a means of avoiding
rising damp and of dealing with significant changes of
site level without having to carry in and compact a large
volume of hardcore.

impervious materials, such as strips of felt or even slate, is

simple to achieve where joists meet dwarf walls, it is more
difficult where joists are built into external walls.

Construction

It is important that spaces under suspended floors are well

ventilated as localized rotting can occur at points where
timbers meet external walls; this will result in subsidence
of floors. Bricks in dwarf walls are laid with 50mm gaps
between them to allow air to circulate and reduce the
chance of rot. Care should be taken that any ventilation
grilles built into external walls remain clear after work is
completed to ensure continued air circulation.

Essentially the same methods of construction are used

as for upper floors, with timber joists, usually at 400mm
centres, supporting timber floorboards. The size of
timbers may be reduced by constructing dwarf walls
below the floor, which will reduce spans. Timbers are
liable to come into contact with moisture wherever
they meet supporting elements. While isolation with

Ventilation

DWARF WALLS
Dwarf walls reduce the span and
therefore the size of joists needed
for a suspended timber ground
floor. The gaps in the brickwork
allow air to circulate, reducing the
risk of rot.
TIMBER FLOORBOARDS
TIMBER FLOOR JOISTS
DWARF WALL

TIMBER FLOORBOARDS
TIMBER FLOOR JOISTS
IRREGULAR JOIST SPACING IN
RESPONSE TO OVERALL DIMENSION
BETWEEN WALLS

SECTION

JOIST SPACING
Joists should be equally spaced,
usually at 400mm centres for
compatibility with standard
composite-board sheets. The
spacing of the final joists should
be reduced in response to site
dimensions (and should never
be increased above 400mm).

Upper floors 91

Upper floors
Timber floors
Timber joists offer the simplest and most common
method of constructing upper floors. Typically, joists
span the shorter room dimension. They are normally set
at 400mm centres with wooden floorboards nailed to
them at right angles to create a comparatively monolithic
structure. The width of joists is normally 50mm but the
depth varies: the longer the span, the deeper the joist.
Longer, deeper joists normally have cross-bracing at
approximately 1200mm intervals to prevent distortion
along their length.

Beams and columns Deep timber joists can span up to

six or seven metres comfortably. However, with greater
spans or heavy loadings normal practice is to reduce
spans with beams, which in turn may be supported on
columns, each of which will require a foundation pad.
Existing beams and columns are usually made of cast iron
or steel, with timber joists resting on top of the beams
or on their lower flanges. Again, it is difficult to justify
ambitious loadbearing capacities for existing columns
and beams, unless they are recent and the original
specification is available.

Altering existing timber floors Even when an existing

Openings When making openings in suspended timber

floor is sound, it may be difficult to prove its suitability

to support a change of use, either because its structural
capacity is unknown or because the cautious statutory
values ascribed to it for calculation purposes will fail to
meet loadbearing requirements. It may be worthwhile to
have a small sample of the timber tested to establish its
bearing capacity.
It is always possible to find a solution by making
significant changes, but to do so often requires elaborate,
costly amendments to floor structures and the elements
that support them. Such changes will require the
contribution of a structural engineer who will be able to
suggest solutions and provide the calculations to satisfy
local authorities, but the extent of work required may
well make a project economically unviable.

floors, to insert a new staircase for example, it is sensible

to contain the new opening within an existing bay the
area contained within adjacent concrete or steel beams.
Cutting through or removing existing beams will destroy
the integrity of the whole structure and the symmetrical
loading of existing columns, thereby distorting the forces
within them. Generally it makes sense to remove as few
timber joists as possible, and it is therefore best to run the
long side of any opening parallel to the joists.

I-SECTION BEAM

TIMBER FLOORBOARDS

TIMBER FLOOR JOISTS

Existing concrete floors

Two alternatives to structural floor timbers are reinforcedconcrete floor slabs and shallow vaults, often with a
core of hollow clay pots. Both are constructed in situ
and supported on beams along each edge. Alterations
are difficult because openings undermine the structural
integrity of the existing monolithic floor.

TIMBER JOISTS ON
STEEL BEAMS
Joists may be
supported on the
flange of an I-section
beam that is then
concealed within
the floor/ceiling
zone. The ends of
the timber joists can
be notched to bring
their upper and lower
edges in line with the
top and bottom of
the beam and ease
the fixing of floor and
ceiling finishes.

92 Floors

Timber joists
MASONRY WALL

PLASTER
SKIRTING

TIMBER JOIST
TIMBER WALL PLATE
MASONRY WALL

SECTION

Joists are the beams that support the components (such

as timber floorboards and plasterboard sheets) that make
up the planes of floors and ceilings. Their depth varies
according to the distance between the structures that
support them. Those used in ceilings are not as deep as
those for floors, as they do not support the additional
loadings of furniture and people. They are usually 50mm
wide, but can vary from 38 to 63mm. Sizes for depth
and width can be identified using tables issued by the
statutory bodies controlling building standards.
In traditional timber construction, joists come into
direct contact with the brick walls that support them.
They may be built into the brickwork or carried on a
timber strip or wall plate, usually 50mm deep, that rests
on the projecting upper surface of a wider wall at the
lower level. If moisture permeates the brickwork, either
directly from the exterior face or by capillary action
from the foundations, it may transfer to, and cause
rot in, the embedded end of joists. In modern timber
construction, joists will normally be supported on joist
hangers. These are galvanized sleeves built into a mortar
course in brickwork or blockwork to keep the ends of
joists free from direct contact with exterior walls during
construction, and to allow bricklayers and carpenters to
work independently of each other.

RESTING JOISTS ON WALLS

TIMBER FLOORBOARDS
MASONRY WALL
TIMBER WALL PLATE

TIMBER JOIST

The width of the wall may be

increased by half a brick thickness
to provide a shelf to support
floor joists. These may rest on, and
be nailed to, wall plates, which
are lengths of timbers bedded in
mortar on top of the projecting
brickwork. While this allows air to
circulate around the ends of joists,
reducing the risk of rot, it does
not eliminate the danger of rot
spreading from the wall plate.

Timber joists 93

TIMBER JOISTS ARE DROPPED

INTO HANGERS
JOIST HANGER BUILT INTO
MORTAR JOINTS IN A BRICK WALL

WALL JOIST HANGERS

Galvanized metal joist hangers
built into courses of masonry walls
provide the most efficient means
of supporting the ends of joists.
Hangers have holes in their
triangular sides through which
nails may be driven into the joists
to improve the connection.

HANGING FROM JOISTS

Joists may support, or be
supported on, other joists. Those
providing support may be deeper
but, more usually, are wider, or
doubled up, to deal with the
extra load without breaking
into the ceiling plane below.
Galvanized metal hangers hook
over the supporting joists, and
the connection to both joists is
improved by nails or screws fixed
through pre-drilled holes.

HANGER HUNG ON AND NAILED

TO BACK OF TRIMMER JOIST
TRIMMED JOIST

94 Floors

Timber rot
One of the most important things to look for when
assessing the condition of an existing building is
evidence of wet and dry rot. Dry rot is perhaps more
insidious since it can travel far into a structure, while
wet rot is localized at a place where moisture has
penetrated the building fabric. Since it is seldom possible
to examine concealed areas of a building before it has
been purchased, problems hidden within the depth of
floor and ceiling voids often only come to light when
work has started on a project, and are difficult to tackle
without removing large areas of floor and ceiling finishes.
Where damage is extensive, the amount of demolition
and rebuilding may so change the nature of the existing
shell that a reconsideration of the strategy for the whole
project may be justified.

CUTTING BACK JOISTS

When rot has been identified,
timber must be cut back at least
1500mm beyond any signs of
damage. During work, sawn-off
joists should be supported by
props to the floor below.

Treating the problem

Both wet and dry rot tend to occur where timber joists
are built into saturated solid masonry walls, and moisture
that has reached the timber is prevented from drying out.
When rot is identified, affected timbers should be
cut back to a distance of about 1500mm beyond the
last visible evidence of deterioration. This necessitates
supporting, or shoring up, the unsupported ends of cut
joists while new sections of clean timber are bolted, and
reinforced with timber connectors (see page 101), to the
ends of the old joists with an overlap of at least 900mm.
Usually if joists are rotted the wall plate on which
they sit will also be affected and must be replaced, again
cutting back 1500mm beyond any evidence of damage.
All timber used in building should now be specified
as having been treated against rot with apressure
impregnating process.

AREA OF ROTTED TIMBER

BRICK WALL

TIMBER WALL PLATE

TIMBER JOIST

INSERTING NEW SECTIONS

Joists may be reinstated by using
treated extension pieces bolted
into the sound ends, overlapping
by at least 900mm. Timber
connectors should be used at bolt
positions to spread and strengthen
the connection.

NEW TIMBER JOIST

NEW TIMBER
WALL PLATE

BOLTS WITH TIMBER

CONNECTORS
EXISTING TIMBER JOIST

Timber floor structure 95

Timber floor structure

Calculating depths

Stabilizing structures

The depth of a floor joist relates to the distance it must

span: the greater the depth, the greater the distance it
can bridge. Dimensions can be calculated by a structural
engineer based on distances to be spanned and loads to
be supported. There are considerable variations within
these calculations: the thickness of joists can vary for
the same depth as determined by the quality of timber
and its approved structural capacity. Tables published by
statutory bodies responsible for approving building works
set out figures on which calculations can be based. For
simple jobs, these can be used by designers to size joists,
as they relate different qualities of timber to the different
categories of loads and identify required sizes. Variation is
possible: a wider joist requires slightly less depth; a better
grade of timber allows a reduction in dimensions.

A timber floor becomes essentially monolithic when

floorboards and ceiling panels are fixed to its upper
and lower faces. However, with deep joists there may
be a tendency for the joist to twist along its length,
particularly because the materials used in most ceiling
construction are not strong. The solution is to brace joists
laterally to prevent the lower edges twisting. This can be
done by inserting short lengths of cut joist at right angles
between main joists, but this uses considerable amounts
of timber. A more efficient solution is to use herringbone
strutting, which braces the lower edges against the
upper, which are in turn stiffened by the floorboards.
The strutting, which need be no bigger than 50 x 50mm,
significantly reduces the volume of timber used.

TIMBER HERRINGBONE STRUTTING

TIMBER FLOOR JOIST

ELEVATION

HERRINGBONE STRUTTING
Cross-bracing prevents joists
twisting on the vertical axis.
The 50 x 50mm section of the
struts minimizes the volume of
timber used.

tip Reading the clues

Upper floors, in the vast majority of cases,
consist of long floorboards, usually about
100150mm wide, laid across and nailed to
floor joists, resting on walls or beams. More
modern construction often substitutes oriented strand board (OSB) or particle boards
that are usually 1220mm long and 600mm
wide, but with both options the longer side
will be laid at right angles to the joist. It is

therefore possible to tell the direction of

joists by looking at the boards and, since
the joists will necessarily be supported
on loadbearing walls, it is also possible to
identify structural walls, which are significantly more difficult to alter or remove. It is
not, however, safe to conclude that a wall
is non-loadbearing simply because it is not
supporting joists it may have other roles.

96 Floors

Steel beams

TIMBER LATERAL BRACING

TO JOIST

The greater strength of steel beams is often used to reduce

the span of timber beams. Their dimensions, including
the thickness of the steel, should always be calculated by
a structural engineer.
Timber joists may rest on top of the steel beam or,
with the I-section beam (often known as rolled-steel
joist, or RSJ), between the top and bottom horizontal
flange elements.
Greater steel thickness can allow shallower or
narrower dimensions. It is often possible to equate the
depth of the steel beam to that of the timber joists so
that the projection of the beam below the joists can be
eliminated, allowing a flat ceiling finish.

FLOOR FINISH
TIMBER JOIST

TIMBER BOARD OR SHEET

SUBFLOOR
STEEL I-SECTION BEAM (RSJ)

STEEL I-SECTION BEAM (RSJ)

TIMBER LATERAL BRACING

TO JOIST
TIMBER JOIST

STEEL I-SECTION STANCHION

OR COLUMN

CEILING

SECTION

STEEL ANGLE CONNECTORS

(BOLTED TO BASE AND
STANCHION)
STEEL BASE PLATE (TO SPREAD
LOAD)

TIMBER JOISTS ON LOWER

FLANGE OF STEEL BEAM
Timber joists may be supported
directly on the lower horizontal
flange of an I-section beam.

TIMBER BRACING
Lengths of timber running parallel
to the steel beam and nailed to the
joists keep them securely located
and vertical. Joists may be cut
around the profile of the flanges
to provide support for board, floor
and ceiling finishes.

Steel beams 97

TIMBER JOIST
BOLTS (AT 900MM
CENTRES)
FLANGE OF STEEL BEAM

WEB OF STEEL BEAM

JOISTS RESTING ON
STEEL BEAMS
When timber joists rest on top of
steel beams they should meet at
the beam but be staggered, with
sufficient overlap to allow a secure
bolt and timber connector fixing
between the two.

JOIST CUT TO PROFILE

Since traditional timber floorboards
run at right angles to the timber
floor joists, it is desirable to have
continuity of support and fixing
over the steel beam. This is
provided if joists project at least
50mm above the beam and are
connected by 600mm lengths of
25 x 50mm timber batten nailed
to joists that line through.

SUPPORT FOR THE JOIST

Steel beams may be pre-drilled,
usually off site, to allow lengths of
timber to be bolted to the lower
flange, both to provide support for
the joist and to allow secure nail
fixings for the bases of the joists.
The connecting strips, fixed flat
against the upper flanges, locate
and fix the upper edge of the joist.

BATTEN (SUPPORT FOR BOARDS

OVER STEEL WORK)
TIMBER FLOORBOARDS
TIMBER JOIST
STEEL BEAM (RSJ)

TIMBER PLATE (FOR NAILS

TO JOIST)
BOLT (IN PRE-DRILLED HOLES
IN STEEL BEAM)

SECTION

600MM BATTEN (SUPPORT FOR BOARDS OVER

STEELWORK)

98 Floors

Planning new structures

Loadbearing capacities
New floors may be comparatively simple to construct, but
it is essential when seeking approval for building work
to prove that existing walls, columns and foundations
can support the increased loading. Different activities
have nominal loadings and even if it is possible to
demonstrate empirically that the structure has previously
accommodated a similar activity, engineering calculations
must be based on the legally designated structural
capacity of the existing materials, which veer towards
the cautious.
Different building materials also have designated
loadbearing capacities, which new superimposed loads
cannot exceed. These do not equate to the bearing capacity
of structural elements: the success of one in dealing with
new loadings does not guarantee the capacity of the other.

Providing additional foundations

If it is not viable to prove the loadbearing capacity
of existing structures, then new loadbearing walls or
columns, each with appropriate foundations, must be
introduced to support the new load.
The principles of these are simple. Every geological
condition has a designated bearing strength, which
determines the weight it can support. The loading

imposed by elements of a building, divided by the bearing

strength of the ground that supports it, determines the
area of the foundation. Generally a column creates what
is known as a point load, where the weight it supports is
directed on to a small area. This may require a reinforced
foundation pad to spread weight and achieve a viable
loading. A wall will spread loading over a larger floor area,
and it may be possible to support additional weight on an
existing reinforced floor slab.
The pattern of loading for existing columns should
not be altered radically. The addition or removal of floor
areas can result in asymmetrical loading and, without
balanced lateral support, this can set up untenable
stresses within structural members.
If new foundations are required (most likely when
new columns are introduced and their point load must be
taken to a bearing stratum at least 900mm below groundfloor level), the damp-proof membrane will be pierced
and must be made good. An even greater problem occurs
when new foundation blocks, or pads, are located close
to the boundary walls with neighbouring properties, as
they may undermine existing foundations. Even when
anticipated, this can lead to significant complications
during negotiations with neighbouring owners for
permission to carry out the work.

PADSTONES
AREA OF SUPPORTED FLOOR

COLUMN EXERTS POINT LOAD

CONCRETE BASE PAD SPREADS
POINT LOAD

AREA OF SUPPORTED FLOOR

LOADBEARING WALL
WALL SPREADS THE LOAD

1 COLUMNS

2 WALLS

Columns concentrate the loading

on a small area of floor, and
are likely to require additional
foundations.

Walls spread the loading over a

larger area of floor, and may not
require additional foundations.

A padstone built into a new or

existing wall will distribute the load
of a beam or joist over a greater
length of wall.
PADSTONE WITHIN WALL
TIMBER JOIST
SUPPORTING WALL

Planning new structures 99

Padstones
Where joists, or more particularly the beams that carry
them, are supported on walls, it is usually necessary to
create a padstone within the width of the wall. This is
in effect a beam, usually concrete, built or cast into the
brick- or blockwork of the perimeter wall, which spreads
the load over a calculated length of wall so it falls within
the permissible bearing capacity of the walling material.

Party walls
Where a new loading is too great for existing walling
material (a problem particularly with some lightweight
concrete blocks) it is necessary to spread it over a greater
area of wall, either by cutting out and rebuilding a section in
a more substantial material or by inserting new columns
integral to or close to perimeter walls. It is not normally
possible to cut into a shared wall to more than half its
width, as the other half belongs to the adjoining property.
If structural work encroaches on such shared, or
party, walls, the client will be responsible for damage to

neighbouring property, so the implications are significant.

The collaboration of a structural engineer is necessary to
advise, produce the calculations and drawings needed for
formal approval, and take responsibility for decisions.
It will also be essential to have a party-wall agreement
with the owner of the adjoining property. This will
provide a written, drawn and photographic record of the
condition of the neighbouring property or properties. This
will make the responsibility for damage clear, so that the
adjacent owner may be compensated for damage caused
by the building work, and the project client absolved from
responsibility for damage that existed before work began.

Existing drawings
Occasionally, particularly in new buildings when a floorto-ceiling height is sufficient to allow the insertion of an
extra floor level, the original designer will have ensured
that existing elements can support additional loadings.
Original drawings and calculations should provide the
information needed to get formal approval for new work.

NEW FOUNDATIONS
When new foundations are located
too close to existing foundations
they can impose unacceptable
extra loading on the bearing
stratum and damage adjoining
structures.

NEW FOUNDATION SLAB

POTENTIAL OVERLOADING OF
GROUND
EXISTING FOUNDATION SLAB

NEW STRUCTURE

100 Floors

Installing new floor levels

If an existing shell has adequate height and the brief
justifies it, the insertion of an additional floor that
occupies all or part of the building footprint can be
rewarding. While a new floor that extends over the total
area is likely to dilute the effect of the original space,
one that occupies only part of the whole can add to the
drama, emphasizing verticality by providing stimulating
new views from above and below.

Construction methods
Aesthetic impact and practical considerations can justify
the comparatively complicated design and building
process. It may be necessary and sensible to take
structural advice from an engineer who will also provide
the documentation necessary to justify the structures
viability to local authorities.
Any efficient solution should aim to use a minimum
amount of material and simple construction techniques.
Structural elements should be easy to install so that work
on the rest of the project is not delayed. Wet construction
poured concrete or masonry walls should be avoided
as both require time to dry before work can continue.

Joists and beams

Timber joists A new floor using timber joists is generally
simplest and easiest to build. Ideally, these should span
between existing loadbearing walls. A joist 250 x 50mm

CONNECTING THE
BALUSTRADE
Balustrade construction may be
simple, but a secure fixing to
the edge of the floor structure is
essential to resist pivotal forces
caused by people leaning on it.
Two alternatives are shown.
1 Balustrade parallel to, and fixed
to, timber joists.
2 Balustrade fixed to steel edge
beam.

can span in the region of 5000mm. If the stair that leads

to a mezzanine runs in the same direction as the joists,
then it will sit efficiently within a simple structural
strategy. If a void is included in the proposal, the joist
adjoining it will provide support off which to build the
essential protective handrail. When joists cannot run
between existing walls, it will be necessary to support
their ends on beams. For modest spans, these may be
no more than bulked-up timber joists, perhaps 75mm
rather than 50mm wide and supporting secondary joists
on joist hangers. For more substantial lengths of edge
beams, more is required. If construction is coherently
planned, the balustrade can, when necessary, act as a
deep beam spanning from wall to wall; it can also, at
least, contribute to the stability of the edge structure
and, at a more ambitious level, support joists.
Timber structural members need fire protection, but
this is usually satisfied by plasterboard and skim cladding.

Laminated timber beams These are composed of long

strips of wood glued together to increase the potential
of timber as a structural material. Their laminated
construction similar to, but significantly thicker than,
the laminations in plywood allows greater depth of
beam with greater structural stability. They also have the
increasingly important quality of being manufactured
from a renewable source using an environmentally

PLANED TIMBER HANDRAIL

PLANED TIMBER HANDRAIL

PLANED TIMBER SPACER

METAL BRACKET
EXPANDED METAL ANGLE
BEAD

CLS TIMBER FRAMING

CLS TIMBER FRAMING

VERTICAL FRAMING
BEHIND NAILED TO JOIST

PLASTERBOARD AND
SKIM

PLASTERBOARD AND
SKIM

VERTICAL FRAMING BEHIND

BOLTED TO JOIST
SKIRTING
SKIRTING

1
SECTION

EXPANDED METAL
PLASTER BEAD
STRUCTURAL STEEL
BEAM

NUT AND BOLT

TIMBER JOIST

TIMBER JOIST

EXPANDED METAL
PLASTER STOP

SECTION

Installing new floor levels 101

Columns
approved production process. They have a good-quality
finish that does not require additional treatment,
although there is no reason why they should not be clad
to be compatible with the interior (see page 161).

Steel beams Steel remains the most common material

for structural beams. Usually lengths are pre-drilled to
accommodate fixing bolts before delivery to site, and
they may also have short steel brackets and plates welded
to them to facilitate fixing. They have the advantage of
being comparatively easy to assemble on site and, once
fixed, provide a stable and dimensionally accurate base
for subsequent work.
They are useful when curved edges are proposed
for mezzanines, for example. Precise radii can be prefabricated off site and, provided the survey of the existing
shell is accurate, become a useful way of setting out and
building complex geometrical forms.
Standard sections provide useful support for timber
joists and comparatively easy fixings for balustrading
and finishes. Steel can be left exposed (if a fire-retardant
coating is sprayed on after installation), protected by
plasterboard cladding or lost in the depth of floors
and balustrades.

Concrete beams Usually pre-fabricated, concrete beams

do not have to dry on site, but do have to be laid in a bed
of wet mortar and must be given time to set in position
before further work can be carried out on and around
them. It is possible to cast fixings for other elements and
finishes into them during production, but generally they
are not as easy to handle or as adaptable as steel. They do,
however, have the advantage of being fire-resistant.

tip Strengthening Timber Joints

Joints are critical to the success of any
structure, including mezzanines, and standard methods of nailing and screwing timbers may not offer adequate performance.
Timber connectors increase the efficiency
of contact when a bolt passes through
aligned holes in the connector and timbers
and is tightened, forcing the double circles of
the steel teeth into the timbers. The circular
plate spreads forces over a wider area of
the timbers, which would otherwise tend to
deteriorate under a concentrated point load.
The teeth eliminate any rotational effect.

Where there are no suitable walls or it is expedient to

reduce spans, it is necessary to introduce columns.

Concrete columns Concrete is generally not suitable

for columns as it must be cast in situ, requiring the
construction of a formwork mould into which wet
concrete can be poured around steel reinforcing rods,
and considerable drying time. Unless a concrete floor
is also being cast in situ there is little to justify its use.

Steel A more viable option is to use a steel column or

stanchion. Comparatively modest loadings can be
supported on an existing concrete floor slab when the
concentrated impact of the stanchion is reduced by the
addition of a flat steel base plate. This allows the loading
to be spread over a large enough area to ensure that it
will fall within the permitted bearing strength of the slab.
The steel base plate is usually shallow enough to allow
it to be contained within the thickness of the floor finish.
An engineers calculations will be necessary to specify
for permissions, sizes, connection methods and grades
of steel.
Timber It is possible to use timber columns, or posts,
which are suitable for light loadings but will still require
engineers calculations to determine their size, the grade
of timber and the nature of the connections. It is not
possible to rest the end of a timber post directly on to a
floor slab, and the section and nature of the material does
not easily incorporate substantial fixings the end grain
will tend to split under loading pressure. It is therefore
good practice to provide a steel sleeve to facilitate fixing
to the floor and to allow a bolt fixing at an adequate
distance from the end of the post (see page 60).

102 Floors

Raising the floor

When it is considered desirable to introduce changes
of floor levels, typically within a comparatively high
ground-floor space, it is again simplest and most
economical to use timber construction. The principle
is familiar. Joists at 400mm or 600mm centres support
either traditional tongue-and-groove floorboarding
or more commonly tongue-and-groove chipboard or
oriented strand board (OSB) sheet, which is better suited
to take sheet or tile floor finishes.
The joists need not be deep because posts can
be used at regular intervals to reduce long spans. The
principle can also be used to create stepped floors for
auditoria when the dimensions of seating and circulation
zones will determine the setting out.
The obligation to ensure physical accessibility for all
building users means that changes in levels require ramp
or lift access. Both consume floor space, and in the latter
case particularly may represent an unsustainable expense.

CONSTRUCTION SEQUENCE FOR

A RAISED FLOOR LEVEL
100 x 50mm softwood posts,
nailed to a 100 x 50mm softwood
base plate, will normally provide
enough support for a raised floor
level. While joists will be spaced
at conventional 400mm centres,
the frequency of uprights will
depend on the length of the raised
floor. A 150mm-deep joist will
allow a clear span in the region
of 3000mm joists may be sized
using statutory tables.

FLOORBOARDS
TIMBER JOIST
TIMBER POST
TIMBER BASE PLATE

Raising the floor 103

TIMBER POST AT 1200MM CENTRES

(CUT TO SUIT VARYING HEIGHTS)
FLOOR JOISTS
TIMBER CROSS-BRACING
TIMBER HORIZONTAL SUPPORT
FOR FLOOR JOISTS
TIMBER BASE PLATE

REDUCING FRAMING FOR

RAISED FLOORS
100 x 50mm vertical softwood
supports, at 1200mm centres,
should be sufficient to carry a
horizontal timber beam that will
support the ends of the joists
at 400mm. The joists, and their
end supports, should be sized
according to the distance they
span and the loading on them.
Cross-bracing will improve
stability.

SECTION
TIMBER JOIST
TIMBER BATTEN TO
SUPPORT CORNERS
CHIPBOARD, MDF
OR PLYWOOD
TIMBER POST

TIMBER POST
BASE PLATE

FRAMING STEPS OR TIERED

SEATING
Variations in the height of uprights
can create different levels for
steps or tiered seating. A span of
1200mm between the front and
back of each level determined by
the width of standard chipboard,
MDF or plywood flooring sheets
will accommodate seating and
provide legroom and circulation
space.

104 Floors

Openings in floors
Existing floors
Generally, when making openings in existing floors the
principle of minimal intervention makes sense. Structural
elements are generally interconnected, and changes will
require elaborate solutions when that interdependency
a crucial part of their effectiveness is compromised.
The impact of new construction on existing elements,
such as adjacent floors and walls, needs to be taken into
account not only when the new structure is complete but
also for the duration of the work, requiring as it may
temporary support. The consequences of structural damage
to the building shell and to adjacent buildings where
the most minor movement can cause expensive damage
to finishes can necessitate elaborate supports. Such
protection is expensive, and the alterations that demand
it can be justified only in more ambitious projects.
If it is necessary to make an opening to
accommodate stairs, ramps, lifts or simply to connect two
levels visually then the viability of the existing structure
must be investigated, and supporting calculations by a
structural engineer will be necessary.
JOIST HANGERS
Joist hangers provide a sleeve
support for trimmed joists, which
have been cut short to make the
opening. The hangers wrap over
and are nailed into the back of
the trimmer joists that are, in
turn, supported on hangers nailed
to the trimming joists. Both
trimmer and trimming joists carry
additional weight. To cope with
this, their width can be increased,
typically from 50mm to 75mm, or
they may be doubled up and the
hangers hooked over both.

TRIMMER JOIST
JOIST RUNNING BETWEEN
SUPPORTING STRUCTURES
TRIMMING JOIST
(MAY BE DOUBLED)
TRIMMED JOIST

Openings in floors 105

NEW OPENING

EXISTING BEAM

NEW STAIR

SECTION

ENSURING ADEQUATE
HEADROOM
The necessary retention of
structural beams can interfere
with headroom on stairs or ramps.
There are precise legal minimum
headroom requirements, so it
is vital to check these are met
at various points throughout a
projects development. The beam
itself may not cause problems
but, if clad for fire protection,
the minimal additional depth
can mean it fails to get approval.
Manipulation of the relationship
between treads and risers should
solve problems but it is quite easy,
particularly if working solely on
plan, to overlook the existence
of an obstruction that cannot be
circumvented.

Basic principles
While it is easier to insert openings into new floors than
into existing ones, the basic principles are relevant to
both. Openings should, as far as possible, sit logically
within the proposed grid of the floor structure, parallel
to joists and within the confines of structural bays. The
location and configuration of stairs is a crucial factor in
how the plan of connected floors is resolved. The designer
must balance the practicalities of construction with the
practicalities of habitation.

Timber joists The simplest undertaking is the insertion

of a straight staircase flight into a timber floor. If aligned
parallel to the joists, it will seldom be necessary to
remove more than two joists, which with joists at 400mm
centres will give a void approximately 1200mm wide.
This reduces the structural demands made on the joists
alongside the opening, which have to take the load of the
truncated, or trimmed, joists.
A joist supporting the end of the cut joists is called a
trimmer; those that support the ends of these trimmers
are trimming joists. It is less efficient to make an
opening with a longer axis at right angles to the direction
of the original joists as this increases the number of
trimmed joists, and therefore also increases the load on
the trimmers. However, it is usually enough to increase
the thickness of these supporting trimmer joists, typically

from 50mm to 75mm, to deal with the extra loading.

It is much more complicated to make an opening
with sides that are not parallel or at 90 degrees to the
joists. It is difficult to make good connections, and the
uneven loading on the trimming joists can distort them
along their length and set up tension at the point of
support that was not anticipated when they were built.

Steel elements Where steel beams form an existing

primary structure they usually have timber joists
spanning between them to support the floor area. It
is comparatively simple to remove all or part of this
secondary structure, but more complicated to interfere
with the steel elements as the removal of one section can
weaken the whole structural network of the building, of
which it is an integral component.

Concrete elements Where concrete beams support

precast concrete planks, the principles for removing
primary and secondary structural elements are the same,
as the planks have at most only a minor stiffening role.
If the floor slab and beams are cast monolithically,
usually with interconnected reinforcing bars, it is much
more difficult to cut openings. It will be necessary to
introduce a secondary structure to support the edges of
the opening during the work, and probably permanently.

106 Floors

FLOOR FINISH

6MM PLYWOOD
TIMBER FLOORBOARDS
TIMBER JOIST

SECTION

Floor finishes
The essential structural components of floor construction,
with the exception of good-quality tongue-and-groove
boarding or sheeting, do not offer an acceptable finish
for any but the most utilitarian contexts. It is therefore
necessary to introduce a subfloor a layer between the
structural floor and the finishing materials. The latter will
often be only a few millimetres thick, and so is vulnerable
to fracturing if laid on uneven or rough surfaces.

New buildings

SOLID TIMBER FLOORS

Preparing for finishes In newly completed buildings,

the quality of structural floors may be acceptable for
many commonly used finishing materials. However,
minor variations in level, which may mean that areas
of sheet or tiles are not wholly glued to the subfloor,
can result in fracturing of brittle materials. Where
undulations occur, a self-levelling screed can be used
this is a very liquid compound that when poured
into shallow areas will spread to match the level of the
existing floor, and is capable of drying, where necessary,
in very thin layers that will adhere to the existing surface.

Traditional solid timber floorboards

are prone to warping and, over
time, seldom provide a completely
level surface. Therefore when
laying tiles, plastic, or even clay, it
is advisable and usually necessary
to lay 3mm, 6mm, 9mm or 12mm
timber-based sheet materials
over them to provide a smoother
surface that eliminates the stress
caused by uneven support and
ensures the distribution of adhesive
over the whole underside of the
finishing material.

Concrete floors A 50mm smooth screed will normally

FLOOR FINISH

TONGUE-AND-GROOVE
CHIPBOARD FLOORING
SPANS BETWEEN JOISTS
TIMBER JOIST

SECTION

TIMBER COMPOSITE FLOORING

The interlocking tongue-andgroove joint and the more inert
nature of timber composite
flooring sheets, which are less
susceptible to atmospheric change
than solid timber, mean that the
resulting floor is significantly more
stable. Consequently it is possible
to lay new floor finishes, with or
without adhesives, directly on to it.

cover the rougher 150mm of a concrete subfloor. Finished

screeds should be of a high enough standard to allow
finishes to be fixed directly to them. A good-quality
screed is achieved by mechanical vibration of the newly
poured concrete. The agitation prolongs its liquid state
and allows it to find its level.
Where the screed itself is intended to be the final
finished surface, or when adhesive will be used to fix the
finish, it should be smoothed with a mechanical grinder
and the smoothed surface painted with a proprietary
liquid sealant to prevent the generation of dust from the
comparatively fragile surface of raw concrete. Sealant
darkens the flat, grey tone of raw concrete and brings
out the natural visual texture that is not apparent in the
untreated material. Screed surfaces can also be cut back
further to expose aggregate for an effect similar to that
of traditional terrazzo. The process is slow and therefore
expensive, but it eliminates the need for a further finish.

Timber-based floors Tongue-and-groove timber

floorboards are increasingly being replaced by composite,
timber-based sheet materials as the preferred finish in
timber construction. Such sheets are cheaper than natural
timber, and the nature of their composition makes
possible a refinement of the tongue-and-groove joint
to provide an interlocking and extremely tight, almost
invisible, connection.

Floor finishes 107

The resulting floor needs little fixing to the joists

since, once joined, sheets become essentially monolithic
and will not move. Boards for subfloors are generally
1200 x 400mm, which also makes them easier to handle
and quicker to lay. Their composite structure makes
them less vulnerable to variations in temperature and
moisture. Even when the impression of conventional
floorboards is required for aesthetic reasons it is now
standard practice to lay a sheeted subfloor before covering
it with an engineered board, a thin veneer of goodquality, decorative timber on a composite board base.
Afoam mat no more than 3mm thick is laid between the
two to absorb minor unevenness. Engineered boards are
essentially unaffected by atmospheric variation and, in
this respect, are superior to solid timber boards.

Traditional timber boards Unevenness is a common

or crudely patched where new service pipes have been

inserted. Undulating surfaces and holes may be repaired
with self-levelling compounds. If the surface is worn, it
should be treated with sealant to eliminate surface dust
that would prevent good adhesion. The patina that results
from wear and tear is sometimes prized as decoration.

problem with traditional floorboards, which tend to bow

across their width over time. Where these have character
and when the intention is to use them as the finish, then
it is normal to sand and seal them. Sanding will remove
most of the high spots. Sealing them will darken and tint
the boards slightly, but will usually accentuate the grain
pattern and give an improved impact resistance.
Over time, existing wooden floors are often damaged
by the installation of electrical cables and heating and
plumbing pipes. Old boards tend to have a different
patina and width from new boards, so it is difficult to
replace them convincingly short of having boards
especially made from the same wood and having them
skilfully distressed, which is expensive and unlikely to
be wholly convincing. The best tactic is to make a virtue
of the discrepancy and to inlay areas of different size and
grain pattern, to present them as a deliberate gesture,
contrasting the characterful shortcomings of the existing
with the perfection of the new.
Where there is serious bowing of boards, it may be
necessary to use a levelling compound or to nail larger,
thicker sheet materials, such as 12mm plywood or MDF,
across the boards to provide a more even surface. Thinner
sheets, such as 3mm plywood or hardboard, may be
necessary because an increase in floor level can cause
problems when the raised section meets existing levels.
Thin sheets themselves have a tendency to distort where
there are significant undulations in the original subfloor.

TONGUE-AND-GROOVE JOINTS

INTERLOCKING BOARDS

Existing buildings
Preparing for finishes When new interiors are inserted
into old buildings that were originally utilitarian or have
become worn from long use, floors will usually require
upgrading, as much for safety as for aesthetic reasons.
Concrete floors Existing screeds may be pitted, friable

The traditional tongue-and-groove

joint is used for both solid timber
floorboards and composite OSB
or chipboard panels. Its function
is to ensure that abutting boards
are level over their width and that

there are no gaps for draughts.

If solid timber boards are used,
nails can be driven into the joist at
an angle through the top of the
tongue to be hidden by the next
board when slid into position.

Self-locking composite boards are

now manufactured and eliminate
the need for all but occasional
perimeter nails.

108 Floors

Finishing materials
A designer may be required to do no more than specify
a floor finish, since the laying of this finish will usually
be done by a specialist following a manufacturers or
suppliers instructions. However, it remains essential to
consider practicalities and realities when selecting the
finishing material.
The floor plane, although apparently a modest
element in an interior composition, is crucial. Users of
any space tend to move around with lowered eyes, and
the floor is almost always in their peripheral vision. It
contributes significantly to holding the other elements
together visually. Its deterioration, if it is carelessly
selected, will quickly devalue the whole.
It is also important to consider the acoustic and
thermal qualities of materials, which can critically
affect users enjoyment of, and efficiency in, a space.
There is always room for originality in the specification
of finishes, but commonly used materials owe their
popularity to their suitability and it is logical to look
among them for a solution.

Stone and clay

Natural stone, reconstructed stone and fired clay tiles
are best laid directly on to a smooth, level screed, using
proprietary brands of adhesive and grout the material
used to finish the joints between tiles. It is possible to
lay tiles on a wooden subfloor if existing timber-boarded
floors are covered with a sheet material, which will
provide a more effective surface for adhesive and ensure
a more level finish. Tiles require very little maintenance,
apart from regular cleaning, and withstand wear from
foot traffic very well.
Stone and clay tiles come in a variety of sizes, up to
600mm square, and are comparatively thick, typically
10mm. The adhesive layer adds an extra 2 or 3mm to the
overall depth of a new floor. This can cause difficulties
where new and existing finishes need to be aligned.
A sloping threshold will provide a smoother transition,
eliminating the danger of tripping and, since the level
change is likely to occur at a door opening, the visual
impact is minimized. With a wooden subfloor, it is
possible to remove the existing boarding and replace it
with thinner sheet material that minimizes the variation
in level, but this is likely to require subtle levelling or
packing to achieve a wholly smooth transition.
Stone colours, textures and tile patterns can be
accurately reproduced with plastic laminates. These
are available on engineered baseboards, usually 100 x

200mm, with interlocking jointing systems that eliminate

visible joints. They also have the advantage of being
easier to maintain, but are palpably ersatz.

Plastic and rubber

Thinner, more flexible tiles are manufactured from
various plastics, rubber and linoleum. The last two
varieties are increasingly favoured because they use
renewable, sustainable sources. A consequence of this,
however, is that they, and rubber in particular, are more
susceptible to surface wear than the best-quality plastics.
All come in a variety of sizes, with 300mm square the
most common. They are fixed with proprietary adhesives
and, because of the precision of manufacture and their
stability under atmospheric variations, they can be
tightly butt-jointed and require no grouting. Joints will,
however, be discernible and will become more obvious
with age. It is possible to get pure colours in rubber tiles
and some plastics, but linoleum and most plastics have
a flecked pattern that is reminiscent of, and can be made
to resemble, stone texture and graining.
These materials are also manufactured in sheet form,
which is wide enough to eliminate the need for joints in
most interior spaces, and are particularly useful in areas
where hygiene is important. Joints between sheets can be
heat-bonded during laying to eliminate gaps entirely.

Timber
Timber floor finishes are popular because they are
perceived to be clean and natural. They offer a range of
grain pattern and tones, but all are inevitably variations
on beige and brown. Some colour tinting of the basic
hue is possible. The most popular variation replicates or
mimics the liming process that tints the wood white.
It is now unusual to rely on traditional loadbearing
plank-like boards to provide the finished floor surface.
While old, worn boards are usually enthusiastically
retained because of their perceived character, it is now
standard practice to lay thin boards usually 10 or 12mm
thick on top of a sheeted subfloor.
While some of these boards are strips of solid
wood, most consist of a thin veneer of good-quality
wood glued to a composite baseboard, which can cope
with atmospheric variations. This reduces the quantity
of expensive timber required. The boards are usually
manufactured in planks, typically 1200mm long and up
to 200mm wide. The width is usually made up of three
strips of substantial veneer.

Finishing materials 109

There is a significant discrepancy in the price

of boards, which directly reflects the quality of their
manufacture and the finishing veneer. The price of the
most expensive examples is linked to the quality of the
real wood veneers used and of the engineered baseboard.
The cheapest wood flooring consists of a very thin
photographic veneer glued to a correspondingly cheap
baseboard. It wears badly and the repetition of wood
grain in the photograph can be obvious. A top layer
of plastic laminate, which can accurately replicate all
timber varieties, offers a more convincing, and durable,
substitute. It is visually convincing but lacks the kudos of
real wood. In descriptions of wood or quasi-wood flooring
products the term veneer refers to real timber and
laminate to plastic or paper replications.
Most boards have a locking joint system, eliminating
the need for nails, screws or adhesives. They ensure a
very tight joint, indistinguishable from those between
the strips that make up the basic plank component.
They should be laid on a soft underlay to absorb slight
local irregularities in the subfloor and reduce sound
travelling between floors. They are laid to stop a few
millimetres short of perimeter walls, allowing for thermal

expansion and contraction. It is desirable to remove

existing skirtings, refixing or replacing them after the new
floor has been laid. The solution of fixing an additional
quadrant moulding to cover the joint when skirting has
not been removed looks unacceptably expedient.

Carpets
Carpets offer the widest range of colours, patterns and
textures and are produced from natural wool and artificial
plastic-based yarns. They are available in rolls up to
4500mm wide, and tiles, usually 400 or 500mm square.
The latter are normally made from artificial fibres
and are primarily intended for working environments.
They are usually fixed with an adhesive, and although the
length of fibre is not great it is sufficient to disguise joints
and give a visually monolithic appearance.
Selection of carpet type must be partly determined
by location and intensity of traffic, and all types of carpet
are classified according to their durability. Carpet in rolls
should be laid on to underlays. Tiles can be laid directly
on to a floor screed or on to composite timber sheets,
which may be subfloors in their own right or coverings
to uneven floorboards.

tip a better expedient

It is not always practical to remove existing
skirtings before laying new floor finishes.
It is expensive, and causes damage to wall
finishes and to old skirtings that may be
prized for their intricate moulding. The usual
solution is to cover the joint with a quadrant
moulding, but this does not blend easily with
floor or skirting. It is better to fix a simple
moulding that will cover the gap to the face
of the skirting and appear to be an integral
part of the original.

SECTION

SECTION

EXISTING SKIRTING

EXISTING SKIRTING

QUADRANT MOULDING

NEW INTEGRATED
MOULDING

NEW FLOOR FINISH

NEW FLOOR FINISH

EXISTING FLOOR FINISH

EXISTING FLOOR FINISH

110 Floors

Other considerations
Conduiting
The floor provides an important zone for the distribution
of electrical cabling and of pipework for both plumbing
and heating.

New concrete floors It is normal for all wiring and pipes

to be laid on the structural floor and the finer mix of the
screed (which contains no large pieces of stone) poured
over them. Pipes are in effect buried and unreachable, but
if the systems are tested before the screed is poured they
should perform satisfactorily because burying protects
them against casual damage.
The only threat will come from future interference
with the screed, but if record drawings are retained
showing the location of service elements, this may be
avoided. Electrical wiring is normally enclosed in a
shallow metal conduit that allows old wiring to be pulled
through and discarded. If new wiring is attached to the
old, it can be drawn through the length of the conduit
in the same operation.

on top of the lath-and-plaster ceiling plane, and this is

still used with limestone chips replacing clinker or sand.

Floating floors Another technique for soundproofing is

to float new floor planes. Resilient strip materials such
as mineral fibre can be laid on top of joists to break the
continuity of hard structural elements. Battens nailed to
the joists maintain air circulation beneath the boards and
reduce the risk of rot.
New floor finishes on top of existing boards or new
subfloors may be laid directly on a mineral-fibre quilt
and, if joints are interlocking, do not need to be fixed
to the joists which further improves performance.

Existing concrete floors With existing concrete floors

it is possible to cut chases, or small trenches, in screeds
to make routes for service distribution. It is not difficult
to make good the physical damage, as long as the
damp-proof membrane has not been affected and visual
evidence of the work can be lost under the floor finish.

Timber floors In timber construction the void spaces

between joists provide generous circulation zones, and
when wiring and pipework (usually of a modest 12mm
diameter) must cross joists at right angles they can
be drawn through holes drilled in the centre of joists.
Holes should be in the centre because this is the least
structurally stressed area in the joist the top experiences
the most compression, and the bottom the most tension.

SOUNDPROOFING:
FILLING VOIDS
Pugging loose material poured
between joists increases the
weight of a floor and cuts down
the vibration and transmission of
sound waves through the void. A
secondary floor finish, laid loosely
over existing boards, will further
reduce transmission.

Soundproofing
Mass and density of flooring is the most significant
component in sound transference. The heavier the
construction, the less likely it is to vibrate or act as a
sounding board for the transmission of noise, so concrete
construction is inevitably effective.

Filling voids With traditional timber floors, voids

between joists and the discontinuity of construction
where floors meet walls create the greatest problems of
sound transference. The accepted solution was to increase
mass by filling the spaces between joists with loose
material, usually clinker or sand, known as pugging, laid

SOUNDPROOFING:
FLOATING FLOORS
A mineral-fibre quilt laid over joists
will absorb sound waves and,
by cushioning the connection of
flooring to joists, softens the direct
transmission of sound through the
structure.

Other considerations 111

Fireproofing
As with walls, standards of fire resistance are legally
required for floors to protect escape routes within
buildings and adjoining property. Different building uses
and numbers of occupants will determine requirements
and solutions, which can be identified in guidelines
produced by the responsible statutory bodies.
A concrete floor deep enough to satisfy structural
demands will almost certainly meet those for fire
resistance. With traditional timber construction, an
acceptable barrier can be achieved by upgrading the
specification of both the floor and the ceiling beneath it.
For example, a half-hour rating which means that the
construction will be capable of retaining its integrity for

PUGGING
(SAND, CLINKER OR
LIMESTONE CHIPS)

a minimum of half an hour when subjected to fire may

be achieved with 21mm tongue-and-groove flooring on
37mm-thick joists and 12mm plasterboard with taped
and filled joints. A one-hour rating can be achieved with
15mm tongue-and-groove flooring on 50mm joists three
layers of plasterboard, which is achieved by using three
layers of 9mm board, laid with staggered joints.
Pipes or ducts that pass through floors represent
potential weaknesses. The problem is overcome by
enclosing them in a non-combustible vertical duct;
making them in non-combustible materials; packing
the void between pipe and floor with non-combustible
material; and reducing the size of elements that penetrate
the floor to minimize their impact on its strength.

SUBFLOOR
FLOOR FINISH

FLOOR JOIST

SECTION

PLYWOOD/BLOCKBOARD/
CHIPBOARD
CEILING
TIMBER BATTEN
SUBFLOOR
TIMBER BATTEN

FLOOR FINISH

INSULATING QUILT
FLOOR JOIST
CEILING

SECTION

CHAPTER 6 CEILINGS

114 BASIC PRINCIPLES

115 SUSPENDED CEILINGS
116 ANGLED AND CURVED CEILINGS
118 PROPRIETARY CEILING SYSTEMS
120 HANGING METHODS FOR PROPRIETARY SYSTEMS
121 OTHER CONSIDERATIONS

114 Ceilings

Basic principles
Traditional construction methods

Modern techniques

Ceilings are, almost invariably, an integral part of floor

construction. Thin timber laths, once nailed to the
underside of the timber floor joists, formed a key for the
three coats of plaster, which might then be embellished
with decorative mouldings.
Timber was the only other ceiling finish, most
commonly as tongue-and-groove boarding, thinner than
floorboards (usually about 12mm) and nailed to the
underside of joists. In more ambitious projects, wider
boards were glued together on a timber frame with butt
joints to make an apparently seamless panel, usually
functioning as a neutral backdrop for the elaborate, handcarved decorative elements, which also served to cover or
distract attention from joints.
Joists that only support ceilings carry a lighter
load than floor joists, and can therefore be shallower.
Regulatory authorities also produce tables that relate
depth and width to span.
Occasionally a secondary ceiling structure was
introduced, usually either to reduce the height of smaller
rooms or to give a distinctive profile to a ceiling. This
used the same principles as floor construction, with
regularly spaced joists that either formed an independent
structure or were hung from thejoists of the floor above.

Modern techniques for ceiling construction are essentially

the same as those used for stud partitions. Plasterboard
sheets (skimmed or drywall), nailed or screwed to the
underside of floor joists, have replaced lath and plaster.
The plasterboard has the same composition as that used
for stud partitions, but smaller sheets are sometimes
favoured as they are easier to handle overhead, despite
requiring more joint filling.

Lights, vents and other surface-mounted and recessed

fittings It is easy to cut plasterboard with a thin, serrated
saw blade and simple to make openings for fittings,
whether pendant or flush. A hole smaller than the
fitting allows connections to wiring and, after fixing, the
fitting will cover rough cut edges. With surface-mounted
fittings, which can be heavy, a flat plate of timber board
or composite sheet that spans between joists can support
screw fixings. Fittings designed to finish flush with the
ceiling usually have a mechanism that locks into the edge
of the cut plasterboard and a rim to cover rough edges.

Concrete floors The underside, or soffit, of concrete

floors can be finished with three coats of plaster. Wiring
can be enclosed in flat aluminium or plastic conduit,
which can be plastered over or run on the surface in
metal or plastic conduit.
BASIC CEILING CONSTRUCTION
In multi-level properties, the
joists that support floors will also
carry the ceiling finish. In singlestorey buildings or top floors,
lighter joists may support only
the ceiling finish.

FLOORING ABOVE
(ON INTERMEDIATE FLOORS)
TIMBER JOIST

SECTION

CEILING (PAINTED PLASTERBOARD AND

SKIM OR PAINTED PLASTERBOARD WITH
FILLED JOINTS)

Suspended ceilings 115

Suspended ceilings
Wiring and pipework for most modest interiors can be
accommodated in the depth of the ceiling structure,
passing when necessary through holes 1225mm in
diameter drilled in the centre of joists. However, in
larger, more highly serviced interiors, the requirements
for service circulation are often greater than can be
accommodated in the depth of floor joists or surfacemounted conduits. In this case, a suspended ceiling
creates a void that allows freer circulation of more
complicated electrical and plumbing provisions and larger
pieces of equipment, such as heating and ventilating
units and ducts. Lowered ceilings can also help with
planning, offering options for the definition of areas that
are more practical than raising floor levels, which requires
substantial construction as well as stairs, ramps and lifts,
which are expensive and waste floor space.

To lower an area of ceiling, lengths of softwood,

known as hangers, are fixed directly to the floor joists
above (or, if a ceiling is retained, to battens screwed to
the original floor joists). The hangers, which support
light joists, may be as thin as 50mm square, since they
are in vertical tension and do not need to resist bending.
The structure is comparatively fragile, so it is better to
screw pieces together, since nailing will destabilize work
already completed. The same rules for spacing of framing
members applies as for any plasterboard cladding, and
every joint should have framing behind it to eliminate
hairline cracking and to ensure the even junction of sheets.

Construction
Suspended ceilings may be supported off timber floor
joists. Existing ceiling material need not be removed
since it is simpler to fix through it than to remove it. If
the existing ceiling is undamaged it will constitute a fire
barrier between two separate areas, reducing the statutory
requirements made of the new construction. In some
locations and for some changes of use, upgrading will
be necessary, but the existing ceiling can be an integral
component of the new installation.
STANDARD SUSPENDED
CEILING
Hangers, which need be no more
than 50 x 50mm, are nailed to
the joists supporting the original
ceiling and dropped to the height
of the lowered ceiling. Horizontal
secondary joists support the new
finished surface.

FLOORING ABOVE (ON INTERMEDIATE FLOORS)

TIMBER JOIST
TIMBER BATTEN (25 X 50MM)
INTERNAL ANGLE SCRIM TAPE
TIMBER HANGER (50 X 50MM)
PLASTERBOARD AND SKIM OR PLASTERBOARD
WITH FILLED JOISTS

TIMBER JOIST (50 X 50MM)

SECTION

ANGLE BEAD

116 Ceilings

Angled and curved ceilings

A flat ceiling is the simplest option to construct, but
given the average ceilings modest practical obligations
it is comparatively easy to shape its profile, producing
something more positive than the minimum boxing that
is required to accommodate services.

significantly harder to fill convincingly, and painted sheet

materials, such as plywood or MDF, will match a painted
plaster finish. Both materials are produced in sheets
specifically designed to bend, with grooves cut into
what will be the convex face.

Construction

Larger curved areas When the area of curved surface

exceeds that of the largest standard sheet then it will
obviously be necessary to consider the nature of joints.
Although they may be filled and rubbed smooth, this is
difficult to do satisfactorily, and it is worth considering
a recessed joint and the pattern it might create.
Wiring for suspended light fittings can be fed
through open panel joints, although care must be taken
during installation to align the suspension point precisely
above the joint, so that the wiring passes cleanly through
the gap and does not lie against one edge.

Support hangers can be cut to appropriate drop lengths

to set up the skeleton form. Plasterboard is suitable for
cladding squared and angled forms but for curves over
large areas it is more effective to use expanded metal
lath. This can be nailed or screwed to the formwork and
finished in three coats of plaster, which may be sprayed
on to ease the operation further.

Smaller curved forms With curved ceilings it is more

efficient to use a smooth composite timber board
as a substitute for plasterboard and skim. Joints are

LARGE CURVED CEILING

The shaded area represents a
plywood rib, cut to define the
profile of a curved, dropped
ceiling and fixed with softwood
hangers to the existing ceiling. The
plywood cladding panel is screwed
to the ribs and the screw heads
are driven below the surface of
the plywood. The indentations are
then filled, sanded and painted.
Since it is difficult to achieve
an invisible joint with abutting
sheets, joints are expressed as gaps
through which electrical cable may
be dropped.

TIMBER GROUND FIXED TO

EXISTING STRUCTURE
TIMBER HANGER

CEILING CLADDING
SHEET (MDF/PLYWOOD/
PLASTERBOARD)

OPEN JOINTS
LIGHT

SECTION

EXISTING STRUCTURE

PLYWOOD/MDF RIB CUT TO

PROVIDE PROFILE FOR CURVES

Angled and curved ceilings 117

tip make a virtue of necessity

It is common practice to lower an area
of ceiling to contain utilitarian elements,
such as air-conditioning ductwork. If only
the necessary minimum area is lowered
(as in 1) the redefinition of the space is
unlikely to be sympathetic to its practical
organization or visual coherence. If the
lowered area is extended in response to
the particular use of the space (as in 2 or
3), defining areas or transitions between
areas, an expediency can make a positive
contribution.

SCULPTING LEVELS
Levels and plan configurations
of lowered ceiling areas may
be varied, within the broad
parameters set by service
equipment. Form is determined
by aesthetic rather than practical
considerations.

LIGHT FITTING IN A
CURVED CEILING
If any details that are prompted
by considerations of the most
efficient construction can fulfil a
second function, a virtue can be
made of the expedient. Here, light
cables fall from the recessed joint
between curved ceiling panels
see detail opposite.

118 Ceilings

Proprietary ceiling systems

Proprietary suspended ceiling systems represent an
economical solution to finishing large ceiling areas,
particularly in offices and other spaces where their
somewhat utilitarian appearance is considered acceptable.
They also offer an easy and quick way of providing a
fairly uninterrupted void for substantial service elements
like air-conditioning ducts.
Most systems consist of lightweight tiles that are
between 300 and 600mm square and manufactured from
mineral fibres. The tiles are inserted into a grid suspended

by wires from the underside of the structural floor above,

and the suspension system offers a comparatively simple
fine-tuning device to establish a level surface over an
extensive area.
The lightweight tiles are usually finished with a
random, slightly indented, surface pattern that has some
limited acoustic qualities and serves to camouflage the
lines of butt joints. The systems also include edge trims
that will generally create a narrow recess at the junction
of the ceiling and the wall.

CEILING PLANK

WIRE SUSPENSION SYSTEM

FOR CEILING SYSTEM
Proprietary ceiling systems use a
minimum of means to cover large
areas of, usually, utilitarian spaces.
The wire suspension system can be
adjusted to refine levelling, and the
tiles are easily and quickly slotted
into place. Tile fixing begins from
the centre and works towards the
perimeter, and the edge tiles are
cut to suit the on-site condition.
Opposite walls will have matching
perimeter conditions.

PROPRIETARY METAL
ANGLE FIXED TO PLANK
SUSPENSION WIRE
HEIGHT ADJUSTMENT
COMPONENT

TILE SUPPORT GRID

PROPRIETARY CEILING
TILE

Proprietary ceiling systems 119

TILES FOR A PROPRIETARY

CEILING SYSTEM
A suspended ceiling with a visible
supporting grid. The individual
tiles, trimmed to fit at the wall
junction, are visible. The system
offers light fittings that fit the grid
precisely. Tiles are easily cut to
receive smaller fittings.

FLOOR FINISH
CONCRETE IN SITU
BACKFILL
PRECAST HOLLOW
CONCRETE STRUCTURAL
PLANK

PROPRIETARY METAL
ANGLE FIXED TO PLANK

SUSPENSION WIRE

HEIGHT ADJUSTMENT
COMPONENT

SECTION

CEILING TILE
TILE SUPPORT GRID

120 Ceilings

Hanging methods for

proprietary systems
Different manufacturers produce ceiling systems
that are variations on a few simple suspension and
jointing principles. A designer needs only to specify the
product, but it may be useful to discuss options with
manufacturers, particularly for awkward sites. Tiles may
be fitted by the general contractor, but on big projects it
may be more efficient to use specialist installers.

Exposed square grids

In the simplest systems, the square grid on to which
square-edged tiles are set is exposed. Tiles can be pushed
upwards for access to services or replacement.

1
EXPOSURE OF GRID JOINTS
There are three basic types of
grid system, each with a different
attitude to disclosure of the grid:
1 Exposed square grid.
2 Chamfered tiles creating a
visible v-joint grid.
3 Slotted tiles creating an
invisible grid.

Chamfered tiles
If an exposed metal grid is unacceptable, a chamferededged tile, with a slot that is pushed over the flat metal
grid member, retains a square grid pattern. The 45-degree
chamfer will allow the tile to be removed fairly simply.

Slotted tiles
The third basic type of hanging method uses a tile with a
square edge and also a slot into which the supporting grid
is inserted. To install this system, it is necessary to work
progressively from one line of the grid usually in the
centre of the ceiling area to be covered so that the cut
tiles are evenly spaced around the perimeter. When the
whole ceiling has been installed and the tiles are butted
tightly together, the grid pattern will become invisible.

Other considerations 121

Other considerations
Sound insulation

Exposing service elements

Since the most serious sound problems will be caused by

noise from floors above, the most satisfactory remedies
are those discussed in the flooring section (see page
110). Where it is not possible to carry out work to a floor
above, it is possible to achieve a degree of reduction if
a secondary, lower ceiling can be built. If the mass of
this can be increased by pugging (see page 110), the
reduction will be significantly improved.
The potential for a lowered ceiling may be limited
by an already restricted height, but since the effectiveness
depends on separation rather than distance there
may be some scope in existing properties for modest
improvement with a secondary ceiling separated from the
original by resilient padding.

In some contexts, and in conformity with a prevailing

aesthetic, it is acceptable to expose ducts and cabling.
A compromise position between this and a suspended
ceiling is to hang a skeleton grid, of timber or metal,
below the servicing elements to create a perforated plane
that will partly obscure them and break up their bulk.
Painting service elements and the soffit of the floor
above the same colour, preferably dark, produces a more
coherent composition.

Fire resistance
Ceilings and floors operate as a single unit in fire
separation, and their requirements have already been
discussed on page 111. It is, however, important to
prevent the spread of fire in what regulations refer to as
concealed spaces the areas above a suspended ceiling.
Large areas of this type will often need to be subdivided
to prevent the spread of fire, by the continuation of
appropriate walls to the underside of the floor above.

EXPOSED DUCTWORK
Some designers are happy
to dispense with suspended
ceilings, and to expose ductwork
(above right). Others prefer a
compromise, and hang an empty
grid below ducts to establish a
notional ceiling plane and help the
ducts recede perceptually (right).

CHAPTER 7 FURNITURE,
FIXTURES AND FITTINGS

124 BASIC PRINCIPLES

126 PORTABLE WORKSHOPS
127 BASE STRUCTURES
128 JOINTING TECHNIQUES
130 DECORATIVE JOINTS
131 JOINING SHEET MATERIALS
133 VENEERS
134 EDGING VENEERS
135 ALIGNING FURNITURE EDGES
136 FABRICATING ELEMENTS ON SITE: BUILT-IN SEATING
138 FURNITURE LEGS
139 FLOATING FURNITURE
140 SHELVING

124 Furniture, fixtures and fittings

Basic principles
It could be argued that there is little need for custommade tables, chairs or sofas, given the plethora of
options available from manufacturers, and it is seldom
economically viable to produce them for any interior. It is
also likely that pieces in mass production will have been
more thoroughly prototyped and tested than is possible
in limited batch manufacture.
However, there are certain elements that consistently
occur in interiors that are designed and manufactured as
one-off installations. Examples are reception desks, which
are the first point of contact for visitors and serve to
establish an organizations identity, and built-in seating
and storage units, which are necessarily designed for
specific physical contexts.

Joinery
Some of these bespoke elements will be constructed
on site, often largely from wood and wood-based sheet
materials because these are more easily worked within the
limitations of site conditions. Such woodwork is referred
to as joinery, as opposed to carpentry, which is larger,
less refined and more structural in effect, the first fix of
timberwork. Joinery will almost invariably use smoothly
planed or prepared timber.

Fabricating furniture off site

It is generally sensible to pre-fabricate as much furniture
and detailed construction as is possible in a specialist
workshop, dedicated to either high-quality generic items
or specialist production dedicated to a particular material,
away from the confusion and unsympathetic conditions
of a building site. Joinery work requires both precision and
a high level of finish that will need protection up until the
moment it is used by the occupants of the interior.
A good workshop will contain the necessary range
of specialist machinery and tools, in a well-planned and
tidy working environment. While hand-crafting is often
prized, for most interior projects it is only with machine
production that the required quality, quantity and price
can be achieved.

Exploring new materials

It is always good practice when working with unfamiliar
materials or unfamiliar techniques to discuss possibilities
and preferred methods of production with the specialist
maker. This can ensure a more refined outcome and
can also act as a stimulus to the designers imagination.
Such collaboration also allows designers to add to their
specialist knowledge and to their repertoire of options for
future projects.

Drawings
The designer is not necessarily required to describe the
making process in detail. It is increasingly common
for a drawing setting out the dimensions and material
specification of the designed object to be given to the
maker, who will then produce a set of drawings which
determine how the designers intentions can best be
achieved using the specialist techniques available. These
drawings will be sent to the designer for approval before
manufacturing begins. Deviation from the intentions of
the original drawing may be discussed and, if generated
by practical considerations, accepted or further refined.

Responsibilities
With such an arrangement the maker is responsible for
ensuring that the quality of the work is satisfactory, but
the designer remains responsible not just for the aesthetic
quality but also for specifying the finishes appropriate to
the objects practical obligations. This requires knowledge
of the performance of materials. Whenever a material,
familiar or not, is being considered for an unusual
context, consultation with manufacturers and suppliers
is important to ensure that the finished product will meet
a projects particular requirements.
The nature of the work will dictate whether it is
necessary for the maker to install on site, and this can
apply to all or parts of the piece. Generally it is better
that installation be done by the maker, who will be
more aware of how pieces should be handled. If it is,
responsibility for any faults will also be clear.

Other considerations
Like every aspect of an interior, the key to a successful
piece of furniture lies in creative consideration of detail,
of the way different materials relate and are connected.
The construction process can often be intricate, and
a good specialist maker will usually be able to achieve
the desired result. However, it is counterproductive to
demand something that will be difficult to clean and
maintain because, no matter how pristine the newly
finished piece may be, dust and wear and tear will
undermine its perceived quality. Natural materials such
as wood and stone tend to acquire character when worn;
manufactured materials do not.

Workshops
The advantage of making pieces in a specialist workshop
rather than on site is that work is carried out in an
uncluttered environment on equipment that may be
fine-tuned to achieve the precision demanded by highquality joinery.

Basic principles 125

MACHINE SAWS
In well-equipped workshops even
the most delicate operations are
carried out on substantial pieces
of machinery that are infinitely
adjustable and wholly stable
throughout. The three saws
illustrated here are each dedicated
to a single operation. The radial
arm saw (left) is used for cutting
timber to length. Cuts may be
made at angles and the extended

bench offers support to the timber,

allowing one-person operation.
The band saw (below) can be used
to cut intricate two-dimensional
curves, while the table saw
(bottom) is used for cutting sheet
materials. The extending grid
elements support the sheet over its
entire area and allow one person
to operate the saw.

126 Furniture, fixtures and fittings

Portable workshops
It is difficult to produce refined objects away from a
workshop but not unusual for simpler joinery work to
be done on site, particularly on small jobs carried out by
small contracting companies or when precise tailoring
to on-site conditions is necessary.
Some power-tool manufacturers are now producing
what are, in effect, portable workshops that deal with
most essential operations, including dust extraction.
If a reasonable working area can be established, there
is no reason why quite ambitious elements cannot be
made on site.

PORTABLE WORKSHOP
In the chaos of a building site the
guide plate for the circular saw,
which slots together from modular
sections, allows perfect accuracy
(top right). The wheeled base
contains a vacuum cleaner that
connects directly to cutting and
sanding tools, removing sawdust
at its source (right). Power tools
are transported in clip-on boxes
(far right).

Base structures 127

Base structures
The base structure of any piece of furniture also
referred to as the carcass on to which final finishing
materials are fixed, is usually not visible and is therefore
manufactured from utilitarian materials. It was until
recently standard practice to build a softwood skeleton
in a specialist workshop, with machine-cut joints
(typically, simple interlocking mortices and tenons)

that were glued together to create the carcass, which was

then made more rigid by the panels of veneered plywood
or other composite board that were screwed and glued
to it. This method of construction has now largely been
superseded by one that makes use of the developments
in manufacturing techniques to utilize the panels as both
structure and cladding.
BUILDING A SITE-SPECIFIC
CARCASS
12 A solid wooden plinth forms
a separate base that will be set
back on the front elevation to form
a toe recess.
34 The base board makes the
plinth rigid and provides a base
on which wooden ribs are built.
57 Horizontal wooden ribs
give lateral rigidity and provide
fixings for the cladding panels
that also increase rigidity and
consolidate angles.

128 Furniture, fixtures and fittings

Jointing techniques
While manufacturing technologies have made the menu
of traditional wood joints evolved under the constraints
imposed by hand tools redundant for the production
of utilitarian connections, the principles of traditional
joint-making have retained an important role in the
production of solid softwood or hardwood elements.
While the joints are now likely to be made by machine,

CROSS JOINT
13 The cross joint locks both
pieces at right angles, and
when glued is very rigid. It
can be repeated to make threedimensional grids that serve as
storage elements.

their form, defined by an understanding of the structure

and capability of natural wood, remains an important
component in the visual vocabulary of furniture
construction. The visible expression of connections
and practical detail is inherent in Modernist design
philosophy, and the expression of traditional joint forms
may be used to signal a commitment to raw function.

Jointing techniques 129

LAPPED JOINT
15 The lapped joint allows the
thickness of framing to remain
constant at junction points, which
makes it suitable for building twodimensional grids. Two variants
are the full lap (3), in which the
framing is the depth of the groove
cut, and the half lap (4), in which
grooves are cut in both pieces of
timber so that surfaces are flush.

DOWEL JOINT

DOWEL

Dowels (short cylindrical lengths

of wood) are inserted and glued
into the abutting faces of timbers.
They form an integral connection
between the two components,
creating an integrated glued
surface significantly more secure
than a simple butt joint.

130 Furniture, fixtures and fittings

Decorative joints
Some of the most interesting traditional jointing
devices worth considering for contemporary detailing
are those, like simple mortice and tenons, in which the
slotting together of components generates patterns akin
to inlays on the surfaces of the finished construction.
Visual definition of the different pieces is the result
of the rougher end grain appearing in the smoother
longitudinal grain. Once the decorative potential of
such traditional jointing is accepted, the application can
exceed the number of joints that is strictly necessary for
practical purposes.

1 Single mortice-andtenon joint

2 Double mortice-andtenon joint

The tenon is cut to fit the mortice

tightly and the abutting surfaces
of both are glued. This increases
the area of glued surface and the
interlocking, if accurately cut,
ensures that the two components
meet at the desired angle.

The additional tenon increases the

area of glued surface and provides
another decorative pattern.

MORTICE
TENON

DOUBLE MORTICE
DOUBLE TENON

tip HIDING SCREW HEADS

Wooden plugs, to cover sunken screw heads,
also create a decorative differentiation of
colour and grain. They are probably most
frequently used in the fixing of stair treads.
1 A hole with a diameter less than that of
the thicker end of the plug is drilled in the
cladding strip or sheet.
2 The cladding sheet is screwed in position
and the plug hammered into the hole until
it fits tightly.
3 The projecting section of the plug is
removed with a chisel or plane, and the cut
end sanded smooth.
It is important to consider and specify the
location of screws and plugs, since they will
be visible in the completed work. Plugs of
the same type of timber as the element into
which they are inserted will still be visible.

PAR TIMBER PLUG

PAR TIMBER STRIP

OR SHEET

TIMBER FRAMING

SECTION

77 7

Joining sheet materials 131

Joining sheet materials

In joinery, solid timber carcassing pieces have now
largely been replaced by MDF, plywood and chipboard.
This is primarily the result of improvements in specialist
machinery and the emergence of highly specialized
workshops that can process large quantities of sheet
material with precision.

Routed joints
Sheet materials can be cut at angles, and a 45-degree
mitre joint presents no problems. It is also easy to cut
sharp-edged channels with great precision. The process of
cutting channels is known as routing and the machine
that carries out the operation is a router. Minimal but
robust joints can be achieved when a channel cut in
one sheet exactly matches the thickness of the sheet to
be slotted into it, providing a tight, fitted housing for a
secure, glued joint.

Advantages This capacity to produce precise elements

and angles facilitates assembly. The two-dimensional
elements that make up a storage unit can double as its
structural members. Each rib is a profiled component that
defines the units cross-section. The monolithic nature of
sheet materials makes them inherently stronger and easier
to construct than the traditional wooden skeleton frame,
which relies on comparatively complex joints and remains
fragile until made rigid by the fixing of cladding panels.

ROUTERS
A handheld router makes a
precisely dimensioned slot in
sheet materials (top right).

SHEET WITH ROUTED SLOT

The slot exactly matches the
width of the sheet to be inserted
into it, and gluing makes a rigid
connection (above right).

ALTERNATIVE ROUTING
TECHNIQUES
1 The lower edge of the upper
panel fits exactly into the slot
made by the router and the joint
is glued.
2 Stopping the tongue short of
the outer edges of both panels
allows the slot to be cut the full
depth of the base, for a stronger
connection.

STEP BY STEP BISCUIT JOINTING

Furniture-making requires precision. Pieces are subject to
close scrutiny and joints must be perfect. While a shadow gap
may provide one answer to the alignment of elements, it is
not a viable option when planes and faces need to be butted
together. Traditional solutions such as tongue-and-groove
joints for the edges of panels, and mortice and tenons for
connecting solid timber framing are being superseded as
a result of the greater use of composite sheet materials and
the development of specialist machinery and techniques.
It has increasingly become standard practice to use
elliptical biscuits for glued joints in all wood and wood-based

elements. The biscuits, made from wood-based composites,

are designed to hold butt joints together exactly and to
increase the area of the joint that may be coated with glue.
They also integrate glue more deeply into the core structure.
Biscuits replace the more traditional dowel insertions,
and, because they are thinner, are easier to insert in the thin
edges of board materials. Recesses to receive them are cut
with a specialist tool that ensures perfect alignment in adjacent
components, which are clamped together to close the joint
and eliminate movement while the glue sets.

Elliptical composite timber biscuits give accuracy and strength to butt joints.

A handheld machine, which fits precisely against the edge of the sheet
material and which can be adjusted to suit the thickness of the boards,
ensures that slots in the two pieces are perfectly aligned.

Biscuits are glued and inserted in each board. Glue is applied to the slots and
edge of the second board.

The two boards are then pressed together and firmly clamped until the
glue sets.

Veneers 133

Veneers
Veneers are thin sheets of timber, usually no more than
1mm thick, shaved in a sawmill from a rotating tree trunk
to make a continuous roll in which the natural grain of
the timber provides a strong decorative pattern. They
are normally cut from comparatively expensive timber,
valued for the complexity of its grain and colour.
The precision of the production process, which
maximizes the number of thin slices that can be shaved
from the same tree, means that the pattern of a batch
from a single source will be very similar and so can
be combined to give a mirrored or repetitive effect.
Similar configurations of grain are often exploited in the
production of door and wall panels to create visual unity.

CONSISTENT GRAIN
Veneers can provide strong
patterns, and when from the same
tree can also suggest continuity
between panels.

134 Furniture, fixtures and fittings

Edging veneers
Veneers of good-quality wood were traditionally glued
to less beautiful but cheaper timber bases, and strips
of veneer were used to cover the more open texture
of cut edges. Today the base layer is more likely to be
plywood or another composite board, which is even
more economical and better able to resist distortion when
exposed to damp or heat. When good-quality materials
are also used in the baseboard, the layered pattern of the
edge may be exposed in an intrinsically modern solution,
where the inherent qualities of basic construction
materials are prized. The closely packed lines of good
plywood are probably the most common example.

Solid wood edges

Exposed edges may be veneered in the same wood as
main planes, but thin veneers are vulnerable, and it is
more usual for a solid wooden strip, with radiused

corners, to be glued to the edge, flush with the face of

the veneered surface. The edge also reduces the likelihood
of the veneer being separated from the base board.
Tongue-and-groove, dowel or biscuit joints strengthen
the connection.
Different production methods for veneers and solid
timber pieces, and the variations inevitable in a natural
material, will produce noticeable variations in tone and
grain. The use of different wood species will make a virtue
of the differentiation.

Other veneers
It is also wise to retain the edging strip when using other
veneering materials, such as leather, plastics and metals.
Edging strips also reduce the likelihood of the veneer
being separated from the base board.

1 MITRED JOINTS
A mitred joint deepens the edge
and implies solidity, and extra
depth stiffens the edge. The
block glued to the inner corner
reinforces the connection.

4
1

2 ROUNDED EDGE
A radiused strip allows the veneer
to be dressed continuously over
the edge.

3 THICK PLYWOOD EDGE

Depth may be increased by gluing

strips of plywood, with the same
laminate pattern to the edge of
the sheet. The internal corner may
be reinforced.

4 SOLID WOODEN EDGE

The edging strip should finish flush
with the face of the veneer.

5 SOLID WOODEN EDGE

A vertical edging strip will increase
apparent thickness and act as a
small beam to increase clear span.

6 TURNING CORNERS

A mitred joint allows the grain of

wood to flow around the corner.

Aligning furniture edges 135

Aligning furniture edges

It is always difficult to line through the faces of furniture
components precisely. The treatment of edges or junctions
in furniture is crucial as it can determine perceptions of
solidity or fragility. If the faces of components that make
up a detail are required to finish flush, there is a likelihood
of misalignments. It is better to make a virtue of this and
allow abutting faces to project or recede.

Cover strips and shadow gaps

The traditional cover strip usually wooden and
decoratively moulded adequately covers junctions and
raw edges. It also encourages perception of the object
as a single piece, in which the relatively large expanses
of unadorned surfaces are secondary to the motifs and
patterns defined by the cover strip.

Shadow gaps
Using a shadow-gap solution, on the other hand, allows
the constituent elements of a piece to be given their own

MISALIGNED EDGES
It is difficult to line through the
faces of abutting elements. Minor
discrepancies make the finished
piece appear poorly constructed.

PROJECTING AND RECEDING

FACES
One solution is to make alternate
faces project or recede to
signal that the misalignment
is deliberate.

significance, and it is also compatible with the Modernist

valuing of simple forms and natural materials.

Finishing with a mechanical saw

It is sometimes practical, when a number of elements
have been bonded together and when an allowance has
been made for a slight reduction, to pass the new layered
face through a mechanical saw. If the material is cut
cleanly, the process will shave a sliver from the original
conjoined faces and leave a perfectly aligned cut face
that may then be sanded.
This process will avoid the minor misalignments that
can make joinery look unrefined, but the junction line
between elements will continue to be discernible and,
with timber, the layering will be further emphasized by
variations in the grain. It is possible to make a virtue of
this layering the priority in detailing is to make it clear
that that is a deliberate intention.

CUTTING FIXED EDGES

An alternative, if elements are
securely fixed together and their
configuration allows it, is to cut
through the composite piece to
create a single plane.

tip Creating the illusion

For aesthetic reasons one may wish a
horizontal surface to appear deeper or
thinner than it need be. This is simply
done by adding a vertical edge to increase
depth (1) or tapering the edge to reduce
it (2). However, both can work only if the
surface is below eye level.

136 Furniture, fixtures and fittings

Fabricating elements on site:

built-in seating
While pre-fabrication in a workshop will ensure the
highest quality of finish, it is sometimes more practical
to build pieces on site, particularly where a location
may necessitate a series of precise one-off adjustments.
The following method of producing and assembling the
components of built-in seating illustrates the principles.
It is simple to cut the required structural ribs, fix
them to a wall for support and connect them with the
linear planes of horizontal seating and vertical backrests.
The connection between vertical and horizontal elements
can be precise and secure if the backrest and seating
planes are routed to receive the edges of the ribs.

Use of a template
Perfect precision is possible if a jig or template is set
up for the marking and cutting of all identical elements.
Minor and frustrating variations will occur if each is
marked out individually and cut out by hand, and time
will be wasted.

Structural ribs
It is easier and quicker to use sheet material and a power
saw on a solid working bench to cut structural ribs if the
same angles, recesses and routings are needed (traditional
softwood-frame construction would produce a series of
what are, in effect, one-off skeleton frames in situ). Each
identical component cut from sheet material becomes a
template for the setting out of the whole, establishing the
precise configuration and the location of joints.

ORDER OF WORK
1 Structural ribs set out the
profile of the seating, screwed to
softwood battens that are screwed
and plugged to wall and floor.
2 Routing on the backs of panels
that form the seat and back
receives the edges of the ribs.
The joint is glued.
3 The cushions for back and seat
are contained within the end ribs
and fixed with hook-and-loop
fastening strips to allow removal
for cleaning.

Fabricating elements on site: built-in seating 137

On-site adjustments
It is important in on-site installation work to anticipate
the likelihood of floor and wall surfaces not being vertical or
level, but variations are seldom apparent until installation
begins. It is therefore likely that it will be necessary to
carry out minor adjustments when, for example, a line
of ribs have been provisionally set in position.
Some may need to be shortened and others packed
out with slivers of wood inserted between them and the
floor in order to provide continuous contact and support.
Packing out is not entirely satisfactory, but it is acceptable
for occasional, minor local variations. If it is efficiently
done, the fit between floor and object should be snug
enough to prevent the packing pieces from moving.
There is always likely to be some insignificant settlement
as new elements are subjected to their final loadings.

CUSHIONS
SHEET MATERIAL FOR BACK AND
SEAT CONNECTS AND STABILIZES
RIBS
UPLIGHTER (OR GRILLE FOR
HEATING SYSTEM)
CAPPING TO SECURE AND
CLOSE TOP OF RIBS

Finishing work
The degree of finessing necessary to achieve a satisfactory
standard will depend on the anticipated finish. If, for
example, upholstery is to cover most surfaces, the
substructure need not be finished to a high standard
and, indeed, should not be since that will add time and
expense.

Upholstery All upholstery work should be carried out

by specialists. Even the simplest fabric-covered foam seat
will be more successful if made with expertise. It is also
important to anticipate the need to clean upholstery
specialists can provide solutions. It is perfectly acceptable,
particularly where a fairly rigid foam core is used, to fix
cushions, both horizontally and vertically, with strips of
high-strength proprietary hook-and-loop fasteners.

SHEET MATERIAL FOR

BACK AND SEAT
CONNECTS AND
STABILIZES RIBS
PROFILE OF
INTERMEDIATE
RIBS

ALTERNATIVE APPROACHES TO
BUILT-IN SEATING
1 The intermediate ribs are cut to
size and angled to provide support
for the seat and backrest panels.
The end rib, which will be butted
to an intermediate rib, may be cut
to a different profile.
2 The back and seating panels
can project beyond the end ribs
to conceal edges and contain
upholstery.
3 The space between rib and wall
may be adjusted to conceal a light
fitting or radiator.

CUSHIONS
INTERMEDIATE RIBS
CUT TO PROFILE
AND FIXED TO WALL

PROFILE OF END
RIB HOLDS
CUSHIONS IN
POSITION

SECTION

SECTION

138 Furniture, fixtures and fittings

Furniture legs
In traditional furniture-making, legs were usually of the
same material as the rest of the piece and were integral to
it, so that the connection was secure. Modern methods,
however, favour lighter construction, for reasons that are
both aesthetic and economic. It is necessary, therefore,
when detailing connections to maximize the area
of contact.

METAL FIXING PLATE

TUBULAR METAL LEG

TUBULAR METAL LEG

THREADED ADJUSTABLE LEG

USING FIXING PLATES

The larger the fixing plate and the
further apart the screws, the more
rigid the leg will be.

FOOT

SECTION

STANDARD ADJUSTABLE FOOT

Floors, particularly in old buildings,
are seldom level, and particularly
for tables it is useful to be able to
make on-site adjustments.

HOLE WITH MINIMAL

CLEARANCE FOR LEG

ADJUSTABLE FOOT WITH

FIXING NUT
The threaded connector allows the
foot to be adjusted to variations
in floor level. When tightened, the
nuts prevent further movement.

TUBULAR METAL LEG

SECTION

SECTION
DOUBLE FIXINGS

THREADED CONNECTOR

With a comparatively deep top

(75100mm) it is possible to fix
the leg on the upper skin after
passing it through a hole, which
provides minimum possible
clearance, in the lower skin. The
second fixing provided by the
tight fit of the leg within the lower
hole gives rigidity.

Floating furniture 139

Floating furniture
Floating pieces of furniture may have novelty value, but
it is important to consider some practical implications
before committing to them.

Position of legs
If the intention is that the piece should appear to float,
it is worth considering setting legs as far back from the
edge of the base as is possible without destabilizing it.
This works well with seating or low display units, and,
with a higher upper surface, deep sides will help disguise,
or draw attention away from, the legs.

Number of legs
SECTION

Four legs will provide secure support. Three legs, carefully

placed, will be adequate if they do not result in overhangs
that are unstable when loaded or sat on. Two legs or one
provide stability if attached to a wide base plate, which
may sit, either freestanding or securely bolted, on the
floor. This last stratagem can only be employed when the
location of the object is fixed and flooring layers are thick
enough to allow concealment.

Additional benefits

SECTION

Floors are frequently uneven, particularly if existing

finishes are retained. The lower edge of pre-fabricated
joinery, made perfectly straight in workshop conditions,
will act as a line against which the most minor
undulations of the floor will be visible to viewers. The
solution is to raise the piece on a plinth, recessed at least
75mm, so that the lower edge of the upper unit holds the
eye and distracts attention from imperfections. The recess
will also protect the piece against damage from feet.
ALTERNATIVE FLOATING UNITS
Concealed legs will give the
impression of floating. Where a
plinth is preferred (bottom), the
almost invariably uneven junction
between the floor and the straight
line of the plinth can be obscured
by the projecting straight edge of
the superstructure.

tip What goes in comes out

If it is possible to push one element inside another,
there can never be enough grip to secure legs,
brackets or any other element. A secure mechanical
or glued connection is essential for rigidity.
ELEVATION

140 Furniture, fixtures and fittings

Shelving
Cantilevered shelving

Suspended shelving

Shelving supported on legs is comparatively simple

to design, but frequently for aesthetic ambitions or
practical considerations, such as leaving floor areas free
of obstructing legs it is desirable to support shelves off
a wall. The simple, inverted L-shaped bracket will meet
practical needs but is too utilitarian for most locations.
Cantilevered wall brackets can provide a solution.
They may be utilitarian if concealed within the depth of
the supported shelf, but when exposed as with a glass
shelf need refinement, with first fixing carried out early
in the construction of the wall.

It is seldom easy to get adequate fixing to an existing

ceiling. Timber joists are unlikely to be conveniently
located and it may be impossible to fix to concrete
floor soffits.
Hanging wires, usually preferred because they are
least visually obtrusive, will not prevent oscillation of the
shelf, however tightly fixed at top and bottom, which is
particularly problematic when displaying fragile objects.
Tensioning wires with a floor fixing will not eliminate
trembling, and applying tension needs strong fixings;
excessive tension may damage existing surfaces. Rigid
ceiling-mounted rods may reduce swinging but will be
visually obtrusive and will not eliminate vibration.

1 CONCEALED CANTILEVERS

2 VISIBLE BRACKETS

The steel bracket with projecting

support arms is fixed to the wall
and the shelf, with holes in its
core to match the location of the
arms, is slid on to it and locked in
position by a set screw through
its underside into the support arm.

Brackets with surface-mounted

back plates may be fixed directly
to a wall. Alternatively, threaded
hollow tubular sleeves can be slid
over threaded support brackets
concealed behind the finished wall
surface. When in position the tube
should conceal rough edges of
the hole. Glass shelves are usually
separated slightly from brackets,
normally by rubber pads, which
eliminate movement.

PLASTERBOARD/MDF
TIMBER BATTEN
FIXING PLATE
GLASS SHELF
HOLE TO RECEIVE
SUPPORT ARM

THREADED TUBE
SUPPORT ARM
WALL BRACKET

METAL SPACER
THREADED ARM

SECTION

Shelving 141

Supporting heavier loads

The conventional cantilever will support light objects,
but with heavier loading, greater depth of shelf against
the wall will brace it against the rotational movement
to which the thinner shelf or bracket will be subjected.
A split-batten fixing, although not essential, will allow
secure fixing and easy fitting particularly, as with
the triangular section below, when the shelf is solid
on all faces.

45-DEGREE
MITRED JOINT
PLANED TIMBER
SPLIT BATTEN
PLANED TIMBER
SPLIT BATTEN
MDF OR PLYWOOD
END CLOSER

SECTION

3 THE TRIANGULAR-SECTION
SHELF

PLANED TIMBER
SPLIT BATTEN
PLANED TIMBER
SPLIT BATTEN
MDF OR PLYWOOD
TO CLOSE ENDS

SECTION

ANGLES UNDER 45
DEGREES ARE TOO
ACUTE FOR MITRES

The upper half of the split batten

is glued to the top and side panels,
the lower screwed to the wall,
with appropriate plugs for solid or
plasterboard walls. In a shelf with
an angle of less than 45 degrees,
the very acute leading edges of
a mitred joint will be particularly
vulnerable to impact. Each of
the planes must be cut to the
appropriate angle a join will
be less apparent on the underside
and should disappear with filling
and painting.

4 THE SQUARED SHELF

While a triangular section offers
the most direct response to the
forces acting on the cantilevered
shelf, the principle applies to any
deep shelf section. Others, like the
square, allow a more robust mitred
upper edge, therefore permitting
use of materials such as plywood
without the need to fill or paint.

CHAPTER 8 STAIRS

144 BASIC PRINCIPLES

146 TIMBER STAIRS
147 STONE AND CONCRETE STAIRS
148 STEEL STAIRS
150 HANDRAILS AND BALUSTRADES
152 CANTILEVERED TREADS
154 SPIRAL STAIRS
156 GLASS STAIRS
157 FIRE REGULATIONS FOR STAIRS
157 RAMPS, LIFTS AND ESCALATORS

144 Stairs

Basic principles
Stairs are a direct response to practical requirements, but
they can also offer the interior designer an opportunity to
create a three-dimensional set piece that can encapsulate
and embellish the aesthetic intention of the areas that the
staircase connects.
When stairs are located within a multi-level interior,
the importance of their being visually integrated is selfevident. However, when they provide the primary link
between levels but are contained in a separate stairwell
as is normally the case when they also act as fire-escapes
it is still important that they sustain aesthetic coherence.
Stairs that act only as escape routes may be treated
in a more utilitarian fashion. While stringent rules, set
out in building regulations, provide clear information
about construction criteria, and permitted dimensions for
the horizontal treads and vertical risers, an ambitious
designer will find scope for creative interpretation by
exploring options for structure and materials.

Types of stairs
There are a number of standard configurations for stair
plans. The decision about which to use is likely to be
based on findings about the impact of their plan on
the plan of the project as a whole, and how it affects
circulation between, and around, linked levels.
It is always essential to test the layout of stairs on
section, since a minimum headroom of 2000mm is vital.
While the height of individual steps varies, 12 or 13 risers
will usually ensure sufficient clearance.

Straight flight This is a single flight of stairs between two

floors. There are legal restrictions on the number of steps
that may be included in one flight. When the height of
legally permitted riser means that the legally permitted
number in a flight must be exceeded, a flat landing may
be inserted this can be added at any position, not
necessarily after the permitted maximum.
A straight flight running parallel to the longer
dimension of a narrow plan will eat less into the room
than a dog-leg or spiral, but, if it connects more than two
levels, it will require a circulation zone for those walking
directly to the next flight.

Dog-leg This configuration doubles back on itself at

an intermediate landing, which will normally provide
support for the top and bottom of the flights that serve it.
The landing need not necessarily be at the midpoint of a
stair, but that is perhaps the most efficient option where
more than two floors are connected, as the circulation
space for users bypassing a floor is thus minimized.

Angled Flights of stairs frequently alter direction through

90 degrees but may be turned through any angle, in
response to site conditions or design choices, as long as
landings have a minimum width equal to that of the stair.
Spiral This has a circular plan with fan-shaped steps that
are either supported on a central column or cantilevered
from the wall so the stairwell has an open central void.

TYPES OF STAIRS
Stairs may be rotated
through any angle
as long as there is
headroom for users.
1 Straight flight.
2 Dog-leg.
3 Angled.
4 Spiral.

Basic principles 145

A quarter of the plan area may be devoted to a landing,

but since this configuration allows space for 13 risers,
acceptable headroom is easily achieved.

Terminology
For efficient communication and credibility, it is
important to use the recognized terms, both generic and
technical, relating to stair construction and components.

String The sloping structural component that supports

treads. There are usually two one on each side of the
flight but one, three or more are possible.

Flight A single continuous run of stair. It may span

between floors or be one of a number of flights, joined
athorizontal landings, that combine to connect levels.

Rise The overall height of a flight.

Going The length of a flight measured on the horizontal.
Tread The horizontal surface on which a user steps.
Riser The vertical surface between treads. These may be
eliminated to create an open-tread stair.
Nosing The projection of the front edge of the tread to
increase its length. It is usually designed to withstand
greater impact and loading and also to offer improved
grip for safety purposes.

Baluster The vertical safety barrier on one or both open

sides of the stair. It may be solid or composed of regularly
spaced upright supports.

Banister The vertical post that supports the handrail,

or banister rail.

Handrail The continuous rail on top of banisters or fixed

to walls enclosing a flight of stairs.

Landing The horizontal area on the length of a flight

that allows users to change direction, or the opportunity
to rest. Its minimum length is determined by building
regulations; its width should not be less than that of
the stairs. It is usually permissible to use quadrant or
semicircular plan forms as long as the radius of the curve
is not less than the width of the stairs.
Stairwell The volume within which a stair is contained.

STRINGS AND RISERS

1 Traditional stairs are usually of
timber construction and have two
sloping edge beams or strings,
timber steps or treads and solid
uprights or risers.
2 Risers may be eliminated to
make an open-tread stair if treads
are designed to cope with the

stresses of spanning between the

strings when in use.
3 Edge strings may be replaced
by two strings set back from
the edge of the treads, a single
central string (as above) or one
asymmetrical string.

146 Stairs

Timber stairs
The traditional stair is a pre-fabricated wooden structure,
made in a workshop and brought to site at an appropriate
time in the contract. If it is installed at an early point, it
will be important that it is protected as delicate edges,
particularly nosings, are easily damaged by heavy use.

Construction
Timber stairs are reasonably complex pieces of joinery,
using routings, wedges and glues. Treads, risers and
two-edge strings form what is in effect a complex threedimensional beam sloping between the lower floor and
the edge of the opening in the floor above.
It is standard practice in all but the widest treads
for the front edge the nosing of the tread to project
about 25mm in front of the face of the riser. In traditional
timber construction the nosing is rounded to eliminate
vulnerable sharp edges; in more modern construction
where greater use is anticipated, or where the quality
of timber is poorer, it is normal to rout out a slot on, or
close to, the nosing to receive a metal insert that increases
its strength. The insert will usually incorporate a rubber
strip to improve grip.
The nosing increases the length of the tread without
increasing the going. There is little room or need for

variation on this standard model. Perhaps the only

crucial decision that needs to be made is about the
quality of timber from which it will be built, and that
may be determined by the anticipated finish. Elaborately
carved timbers were integrated in grand historical
examples of wooden stairs, and their memory persists in
the simple lathe-turned banisters and fretwork patterns
in more modest contemporary examples.

Open-tread stairs
Traditional stair construction tends not to offer the visual
potential required in many modern installations. The
most frequently used variation is the open-tread stair.
This involves omitting the riser, which has a significant
structural role in standard timber construction and
contributes to the integrity of the overall structure.
Without the riser, treads are liable to critical bending
under use. While they may not break, they are liable
to excessive bending, which will be both disconcerting
for users and likely to damage joints. Various means
of reinforcing treads are available. Consideration of
materials is prompted by practicalities. There is no single,
entirely objective, right answer. The final decision is most
likely to be based on aesthetics.

TIMBER TREAD
STRING

TIMBER TREAD
STEEL REINFORCEMENT

SECTION

TREAD MAY BE REBATED TO

FINISH FLUSH WITH ANGLE

SECTION

STEEL ANGLES

STEEL T-SECTIONS

Timber treads are supported on

steel angles, which also protect the
edge of the timber.

Timber treads are centrally

supported on steel T-sections.
Supports must be wide enough
apart to prevent pivoting during
use.

Stone and concrete stairs 147

Stone and concrete stairs

Steel angles Timber can be supported by steel angles on
the front and rear edges of the tread. An angle with an
upstand of 2025mm will usually be enough to provide
the necessary additional support. Timber treads may be
routed to create a recess into which any metal supports
may be set, flush with the face of the timber.

Stone

Setting in strings When the strings are set in from the

Concrete

edge of the stair, the reduction in the unsupported span

may fall within the treads bearing capacity. The strings
will also be located more directly under users feet, which
will further eliminate fixing. Support brackets should be
pre-drilled to allow screw fixing, from below, into the
timber, and the screw can be countersunk if the hole is
tapered to receive it.

Reinforced concrete offers an equivalent solidity to the

stone stair and may also be constructed of precast tread
and riser units built into one or more supporting walls.
It is, however, more common to use a single precast flight
to span the distance between floor levels.
While the concrete may be polished, the normally
rough surfaces of the precast unit require the addition of
better-quality finishes. Timber or ceramic and plastic tiles
are commonly used for treads and sometimes risers. Sides
and soffits are usually plastered.
Stairs with a polished-concrete or tiled finish usually
incorporate a ribbed metal-and-rubber strip close to the
nosing for safety.

Lamination Timber can begin to match the structural

capacity of steel if it is converted into laminated beams,
which are bulkier than steel but, because they are
manufactured to exploit the appearance of the material,
do not require further cladding or decoration.

Historically, the grandest stairs tended to be cut from

stone with pre-fabricated, usually interlocking, tread
and riser units spanning between masonry walls, or, in
the case of dog-leg plans or flights within large spaces,
cantilevered from stairwell walls.

RUBBER NOSING

NOSING IN CONCRETE STAIRS

A steel strip provides a strong

front edge while the rubber insert
behind supplies grip.

A series of grooves cut into the

leading edge of concrete stairs can
provide extra grip.

148 Stairs

Steel stairs
As steel often provides support for treads it may be more
practical, and visually consistent, to switch to steel strings
also. That, in turn, may lead to consideration of metal or
glass treads. The structural capacity of steel allows greater
freedom, for instance in the configuration of flights and
in the placement of strings. Steel members will normally
require a corrosion-resistant finish.

Single strings
Two edge strings are often replaced by one, normally in
the middle of the flight, to create symmetrical loading. It
is feasible to offset the string, or to use only a single edge
string with cantilevered treads, but with asymmetrical
loading the structure will have a tendency to distort.
If steel sizes, joints and connections to floor planes are
properly engineered, the structure will be stable.

SECTION

TIMBER TREAD
STEEL FLAT
SCREW
STEEL TUBES
STEEL STRING

Construction methods

ELEVATION

WOODEN TREADS ON A STEEL

STRUCTURE
Wooden treads, screwed to steel
flats, are welded to steel tubes,
which are welded in turn to a
tubular steel string. This separates
elements and minimizes the bulk
of the stair.

Strings Steel strings can be cut to mimic a conventional

stair profile but it is more common for them to be treated
as straight-inclined beams of any of the standard steel
cross-sections. These cross-sections from the most
familiar C, I, T and hollow rectangle to more refined
circles and ellipses help determine the nature of the
bracket that connects tread to string. Steel treads may be
directly welded to strings and are usually pre-fabricated
in a workshop. If a weld is to be visible, the join may be
smoothed using a power grinder.
String-and-bracket construction Brackets will usually
be steel, connected to the string by welding, riveting or
nut and bolt. The last option is particularly suitable for

Steel stairs 149

SERRATED STEEL
STRING

ANGULAR FOLDED PLATE

A sharp folded-steel profile is made
rigid by welding to a continuous,
serrated steel string, which is set
back from the edge to accentuate
the angled profile.

CONTINUOUS
FOLDED STEEL PLATE

assembly on site. Welding is usually done in a workshop;

if a weld is to be visible in the final construction, the join
may be smoothed using a power grinder.
The shape of a bracket will depend on how it is
required to support the tread. In its simplest form it
need be no more than an angle, welded or bolted to the
string, to which the tread is in turn bolted or screwed.
In other situations, some understanding of how loads
are transmitted through materials and how stresses are
created in structural members will suggest the most
effective shape for a bracket this can be refined in
collaboration with a structural engineer.
It is possible to use a range of materials for the tread
as long as they are capable of withstanding wear, which
will be concentrated in a few localized areas. Steel treads
can be moulded or textured to improve grip.

Folded-plate stairs The thinnest tread-and-riser profile

is achieved by a folded-plate stair either pressed
from a continuous steel sheet, with the angles slightly
rounded, or welded for a more angular profile. The threedimensional element formed by the monolithic sequence
of treads and risers needs stiffening along its length to
prevent sagging. This can be done discreetly with one
or more serrated plates fixed, usually by welding, to
the underside of the folded profile. One or more edge
beams, welded or bolted to the profile, will fulfil the same
structural role.

Steel rods Steel treads may be connected to strings by

TUBULAR STEEL
STRING
RADIUSED
FOLDED PLATE
SPOT WELD

RADIUSED FOLDED PLATE

A steel sheet may be moulded in a
press to make a continuous profile
with radiused junctions of treads
and risers. The string may be
continuous, as above, or modular
and spot-welded to provide the
necessary stiffening.

steel rods, which may be used to create complex threedimensional skeletal beams, providing the necessary
structural depth but eliminating visual bulk (see page
156). When creatively engineered such structures
can employ a combination of thin, stiff compression
members and even thinner tension wires. The visual
permeability of such a structure makes it particularly
appropriate for stairs using glass treads. It is usual for
the steel to be highly polished or chromed to create a
reflective finish analogous to glass.

150 Stairs

Handrails and balustrades

Handrails
Even in the narrowest flights of stairs it is normal to
provide a handrail, which must run parallel to the slope
of the stair and should be sized to be comfortable to
grip. A rail that is too small in diameter is as awkward as
one that is too big. Safety laws determine the distance
between the individual elements supporting the handrail,
and this in turn influences structural options.
A handrail can usually only be fixed at its base, and
the chief loading exerted on it is lateral and at the point
furthest from the fixing. It is therefore essential that the
connection of vertical handrail support and stair structure
be capable of withstanding significant pivotal loading.

HANDRAIL
PIVOTAL FORCES ARE
EXERTED IN BOTH
DIRECTIONS

BALUSTRADE (AT 100MM

CENTRES)

Balustrades
In traditional timber construction handrails are supported
on thin timber posts, usually moulded and referred to
individually as balusters or banisters. Safety regulations
usually result in two uprights per tread, a frequency that
creates a combined strength capable of resisting all but
the most extreme lateral loading. A timber baluster, glued
into a precisely cut mortice in the string, will become an
integral component of the string. A banister is fixed at its
base, and the chief loading exerted on it is lateral and at
the point furthest from the fixing. It is therefore essential
that the connection of banister and stair structure be
capable of withstanding significant pivotal loading.

Advantages of steel components

A steel structure not only offers components with an
inherently greater strength than timber equivalents,
but also fixing methods whether welding, bolting or
screwing that add to this. If the longer dimension of
a baluster section is used at right angles to the direction
of the load applied to the handrail, it will have a better
resistance to bending. When uprights are widely spaced
a structural engineer should determine sizes.
Safety legislation, however, will normally require
that the intervals between components be no greater than
100mm, but the steel members necessary to achieve this
can be significantly reduced in size, to thin metal rods or
thinner wires, and can run parallel to the string between
more widely placed uprights. Wires will normally pass
through holes drilled in the centre of the structural
uprights, and be tensioned, after installation, with a
turnbuckle. Linear elements that run parallel to the slope
of the stair are visually more integrated. The malleability
of steel also makes it easier for components to be shaped
to maximize resistance to lateral loading.

TOP AND BOTTOM

FIXING BOLTS EXERT
COUNTER FORCES TO
PIVOTINGS
STAIR TREAD

STAIR STRING

SECTION

PIVOTAL FORCE ON HANDRAILS

Handrails are subject to significant
pivotal forces as stair users lean
against, and pull, them. For
stability they need secure fixing
at base level. Regular fixings need
to be evenly spaced to avoid the
tendency to pivot.

Handrails and balustrades 151

HANDRAIL (TIMBER OR
METAL)

HANDRAIL (TIMBER
OR METAL)

FIXING BRACKETS

BALUSTERS (AT 100MM

MAXIMUM CENTRES)

BALUSTERS (AT 100MM

MAXIMUM CENTRES)

TOUGHENED GLASS
SHEET BALUSTRADE

METAL FIXING (BEDDED

IN CONCRETE STRING
OR WELDED TO STEEL
STRING)

STAIR TREAD
STAIR STRUCTURE

FINISHED TREAD

STAIR STRING

TREAD SQUARED AT
FIXING POINTS

STAIR STRUCTURE

SECTION

SECTION

HANDRAIL FIXING IN
CONCRETE TREAD
Fixings for handrails may be cast
into concrete treads or into floors
and the handrail uprights then
screwed or bolted to the fixings.

HANDRAIL BOLTED TO TREAD

Holes may be cast or drilled into
treads to accommodate bolts
or screws that engage with the
threaded core of the vertical
hollow rod. The treads underside
may be shaped to allow a squareon fixing and the load further
spread by large-diameter washers.

152 Stairs

Cantilevered treads
It is possible to cantilever the treads of straight and
curved flights, but this makes serious demands on the
structure of the supporting wall. The pivotal action of the
tread when stood on will require a substantial fixing and
will transfer significant asymmetrical loadings to the wall.
An engineered, well-built masonry wall, or an in-situ
concrete wall, should have the cohesion and stability
necessary to support cantilevers either built in during
construction or securely fixed later. Where such heavy
construction is not possible or desirable, a supporting
structure, normally pre-fabricated steel, may be hidden
in the thickness of a lightweight, non-structural wall.

Structure of treads
A cantilevered tread must itself have substantial structural
strength to support the loadings imposed on it. This can
be achieved by increasing its depth and by understanding
how forces acting within a tread can determine its profile.
With concrete treads this usually involves a tapering away

from the wall. With steel treads it will be sufficient to turn

down the edges, which then may or may not be tapered.

End plates
If a tread cannot be inserted into a wall, a wall plate, fixed
with expansion bolts and lying flat against the walls face,
works as efficiently as an embedded connection. Bolts need
only be located at the top of the plate, where they support
weight, while the plate spreads the stress of rotational
movement over an area of wall big enough to absorb it.

Finishing
If treads are built into a wall, detailing of the finish
around them is important. There is likelyto be flexing
in any cantilever tread, and if this is not allowed for,
adjacent finishes will crack. A cover piece can be fixed to
the tread, which moves independently of the wall surface,
or if a recess is created at the connection point, the tread
can flex without damaging the finishes.

STEEL TREADS

CONCRETE TREADS
Smooth precast treads are
supported on a central string, cast
in situ. Holes cast in the treads
at manufacture accommodate
expansion bolts that tighten into
holes cast in the string.

Cantilevered steel trays, whose

upturned edges contain concrete
treads, are welded to right-angle
brackets that are, in turn, welded
to I-section strings. The balustrade
uprights are big enough to resist
rotational movement, and the
balustrade rods, welded to them
to comply with safety legislation,
follow the gradient of the stair.

Cantilevered treads 153

SUPPORTING WALL

SUPPORTING WALL

CANTILEVERED TREAD

CANTILEVERED TREAD

COVER PIECE

RECESS IN WALL FINISH

WALL FINISH

SECTION

SECTION

COVER PIECE

PRESERVING FINISHES

A cover plate will mask any limited

damage to finishes around the
junction of a cantilevered step and
wall. Visually the tread and plate
will be perceived as a unit fixed to
the wall.

If finishes are stopped short on all

sides of the cantilevered tread (as
above) they will escape damage
from movement of the tread under
use. Visually the recess suggests
that the tread is penetrating or
emerging from the wall (right).

WALL PLATE
TREAD
STRUCTURAL BLADE
WALL PLATE

As well as allowing treads that

cannot be inserted into a wall
to be cantilevered, wall plates
can allow comparatively thin
treads to be cantilevered. The
tread is strengthened by a central
blade, increasing its depth and
transferring loading forces back
to the supporting structure. The
wall plate, pre-drilled for fixing
bolts, spreads the load and may
be tapered, since the greatest
resistance to bending is necessarily
at the pivoting point.

154 Stairs

Spiral stairs
With both steel and laminated timber it is possible to
curve strings. However, the curved or spiral stair is not
necessarily a space-saving option. It cannot be located
in the comparatively narrow zone of the straight flight,
which makes minimal demands on surrounding floor
structures. A spiral requires at least a two-metre-square
area, and significantly more in public buildings. The
area of tread next to the centre of the staircase is too
constricted to be usable, and is discounted in the
statutory formula for calculating the width of spiral
flights, which require a radius greater than the width
of an equivalent straight flight.
Spiral stairs are almost invariably pre-fabricated,
often as individual tread elements that thread over or are
bolted on to a central vertical support. Since each tread
is, in effect, a cantilever, the flight is subject to complex
asymmetrical loadings and requires very secure fixings at
top and bottom. The involvement of a specialist engineer
at an early stage is recommended.

STEEL PRE-FABRICATED UNITS

In the construction of a steel spiral
stair, pre-fabricated units are
threaded over a structural post
that spans from floor to ceiling.
They are fixed in position by
screws or bolts.
In this example, the edges
of the tread are turned down to
give greater resistance to bending
under use, and drilled to receive
the handrail uprights. One edge of
each tread is positioned below the
tread above it and an upright is
shared by the two, which increases
the rigidity of the whole.

CONCRETE PRE-FABRICATED
STAIRCASE
If the visual effect of the steel spiral
is usually that of a lightweight
structure, concrete pre-fabricated
and reinforced units suggest a
more solid and monolithic object.
Concrete units may be threaded
over a structural spine, but it is
more usual to assemble them, with
the necessary temporary support,
and to pour concrete into the tube
created by the hollow cores of the
central pivots. Tread units may be
moulded to create either a stepped
or a continuous soffit, which may
also be plastered to eliminate joints.

Spiral stairs 155

SECTIONAL ELEVATION

CONCRETE PRE-FABRICATED
TREAD UNITS
Such pre-fabricated tread units
may also taper in section and
create an open-tread effect. If
fixing holes are made in each unit
then they may be connected by
the handrail balusters for greater
rigidity.

tip Getting in line

The height of a handrail on a landing,
balcony or mezzanine is required to be about
100200mm higher than that on a stair.
Therefore, if the last riser is in line with
the edge of the floor, a visually awkward
connection between handrails for stair
and upper floor will result. One solution
is simply to leave a gap between the two,
although this may not be allowed by building
regulations. Another, if there is space on
the plan, is to project a portion of the floor,
corresponding in depth to a section through
the stair, back to allow the stair handrail
to gain the height necessary to meet the
horizontal rail without any adjustment to
its angle.

900

900

SECTION: EDGE OF FLOOR IN LINE WITH

NOSE OF TOP STEP

SECTION: FLOOR STEPPED BACK TO

INCORPORATE TOP STEP

156 Stairs

Glass stairs
Stairs are frequently used to provide visual drama, and
a stair that uses glass and a delicate metal structure
contradicts intuitive perception of stability and strength.

Steel troughs
Toughened glass can easily fulfil the load-carrying duties
of a stair tread. The simplest application is to provide an
edge support on each edge so that the glass is dropped
into and securely held by its own weight in a shallow
steel trough, which in turn takes on the additional
structural role of connecting the strings. There is no
reason why strings should themselves be metal rather
than wood, other than that hard, sometimes reflective,
stainless or chromed steel surfaces have some affinity
with the surface qualities of glass.
Variations on this trough principle can evolve to
complement a range of ambitions. The structural support
can be located under the width of the tread, and its crosssection selected for an aesthetic fit. Glass is normally
pre-drilled to allow for fixing with bolts to the structure,
and fixing details, which are likely to be visible from most
angles, must be carefully considered.

Rods and wires

The most extreme option is to combine glass treads
with a skeletal steel structure in which the solid plate of
the string is replaced by a complex matrix of rods and
wires in compression and tension. Such solutions take
engineering possibilities to extremes; the glass treads
can take on a structurally significant role as plates that
can brace angles and stiffen the web of rods and wires.
The glass may be pre-drilled to accommodate fixing
bolts, or clamped in place. This solution creates a visual
complexity in which the expression of form and structure
gains the status of decoration.

Treads
Whenever glass comes into contact with steel or any hard
material, whether laid in a supporting tray or bolted into
position, the junction should be cushioned by a resilient
rubber or silicone strip. Transparency can be embarrassing
in some circumstances, but it is possible to specify an
obscured glass finish that will not prejudice the sense of
fragility too critically.
Glass is robust but extremely smooth, and can
therefore be slippery, especially when wet, so its location
in an interior needs consideration. Surface texture is
possible but tends to collect dirt and stain permanently.
Conventional metal and rubber solutions, which may
be bonded to the surface, are at odds with the materials
transparency.

Ramps, lifts and escalators 157

Fire regulations for stairs

Ramps, lifts and escalators

In any multi-storey building, designated escape stairs

are crucial to the fire-escape strategy. Not all stairs need
be escape stairs, and may therefore be designed with a
greater degree of freedom. The voids created between
floors by non-escape stairs can infringe regulations
relating to the spread of fire and smoke, and may need
to be enclosed.
Escape stairs must provide a route, protected from
fire and smoke, that allows a buildings occupants to
escape from, and bypass, outbreaks of fire. Escapees
must not be required to re-enter the main volume of the
building. The escape stair should lead directly to the open
air. It cannot, for example, deliver escapees to an internal
entrance lobby. Lifts and escalators may not be used as
a means of escape because they rely on electrical power
supplies that will fail in a fire.
Local building laws will have a significant impact
on details of escape-stair construction. The regulations
governing dimensions of treads, risers and landings,
the fire-retarding capacity of materials and construction
techniques will all have a significant impact on the
palette of materials and impose restraints on planning
and elevational treatments of the stairwell enclosure.
This will be particularly problematic when an
escape stair also acts as the primary connecting stair
between separate floors, when it makes sense to combine
circulation and escape routes to avoid the loss of useful
floor area. The mandatory physical separation of escape
stairs makes visual integration of vertical circulation
routes difficult. While glass with an acceptable level
of fire resistance is available, it is too expensive for
most interiors.
The complexity of the permutations of permitted
options makes consultation with the body responsible
for approving proposals important from very early in
the design process.

Ramps

GLASS AND STEEL STAIR

Glass components for the
stair treads and balustrades
are supported by a delicately
engineered steel structure.

STRUCTURAL DETAIL
Elements within the steel structure,
in compression or tension, support
the glass treads.

Ramps provide disabled access. Their length is determined

by legislation, which means that it is usually difficult
to connect full storey heights particularly because the
longer the ramp, the shallower the gradient permitted in
order to reduce the physical strain on wheelchair users.
Legislation also limits inclined length. A flat landing
must be provided on long runs to allow disabled users
an opportunity to rest.
A long ramp takes up a significant floor area and
obliges users to walk significant distances. It is sensible
also to provide a stair, to give able-bodied users the
option of a more immediate link between floors, but a
ramp does solve the access problem for modest changes
in level and, if strategically placed to complement
circulation patterns, can circumvent the need for stairs.
Ramp structure is similar to that for a horizontal
raised floor. Joists normally run parallel to the length
of the ramp and are installed at the gradient of the
ramp. The subfloor and finishes are applied as for a
conventional floor. Balustrade and handrail construction
follow principles appropriate to stairs and balconies.

Lifts and escalators

Where ramps are impractical, or where it is considered
appropriate to offer a more direct method of circulation
between levels, lifts offer the most effective option. While
expensive to install, they use very little floor area and
technical improvements have significantly reduced the
area required for machinery.
Designing, building and installing lifts is a specialist
activity; a designer is likely to be responsible only for
the selection of finishes for the internal surfaces of the
lift car and for ensuring that the surrounding structure
is adequate to cope with the installation. The decision
about type of lift is likely to be made in collaboration
with lift manufacturers, and may involve no more than
making a selection from the standard options on offer.
Similarly, the mechanical design, construction
and installation of an escalator will be carried out by a
specialist manufacturer. There is some room for selection
of materials for balustrades and the cladding that conceals
the underside of treads and machinery. Revealing these
through glass panels is an option. Designers do need to
give particular thought to the junction of the underside
of an escalator and a floor.

CHAPTER 9 MATERIALS

160 TIMBER
162 MDF
163 PLYWOOD
164 PLASTERBOARD
165 STEEL
165 ALUMINIUM
166 GLASS
167 ACRYLIC
168 FIXINGS

160 Materials

Timber
Timber is the most versatile building material. It can
be used for the crudest, hidden structural framing or as
a finishing material of the highest quality. It is easy to
work, durable and also offers a wide range of aesthetic
options. Most timber for the building industry will be
treated against rot, but it is important to check that
structural timbers in particular have been impregnated
under pressure with wet- and dry-rot-resistant liquid.

Softwood and hardwood

There are two categories of timber: softwood and
hardwood. Softwood comes from fast-growing, usually
coniferous, trees with widely spaced annual rings.
Hardwood comes from slow-growing, usually deciduous,
trees with closely packed rings. It is the latter that is most
prized as a finishing material because of its rich range
of tones and visual textures. The most exotic examples
are frequently the product of rare trees, and their felling
is now severely restricted or illegal. It is the designers
obligation to minimize or reject their use and to check
that any wood from protected sources, if it is to be used,
has been legitimately felled.

Types of timber
When a tree is felled, branches are stripped from its trunk
and those not large enough to be converted to standardsized planks and strips are reduced to the strands and
fibres used to make composite building boards, such

as oriented strand board (OSB) and medium density

fibreboard (MDF). The trunk is reduced to the various
standard-sized sections used in the building industry.

Sawn timber The felled trunk is sawn along its length

and converted into various-sized planks, the largest
coming from the centre of the trunk and the smallest
from the outer extremities. Cutting is done on a large
circular saw. The resulting faces of the planks are rough, torn
by the teeth of the saw blade. Sawn wood is primarily
used for structural elements, most commonly joists.

PAR timber All other timber used in the construction of

interiors is planed smooth on all its sides so that it offers
precise surfaces for intricate assembly and finishing. It is
classified as PAR, an abbreviation of planed all round.
Upgrading sawn timber to PAR, which is cut to
standard dimensions (although these can be modified as
specified), involves shaving 3mm off each face so that a
100 x 50mm sawn cross-section is reduced to 94 x 44mm.
These dimensions are generally accurate but, because of
the organic nature of the material and its susceptibility to
environmental conditions, there can be some, very slight,
variation and this must be borne in mind when detailing.
In recognition that exact precision cannot be guaranteed,
PAR timbers have traditionally been described as ex,
followed by the original dimension a 94 x 44mm PAR
timber would thus be described as ex 100 x 50.

FORMS OF TIMBER

GRAPHIC CONVENTIONS

Sawn timber (left, below) has the

rough finish left by the blade of
the saw that cut it from the tree
trunk. It is suitable for structural
framing. When sawn timber is
planed all round (PAR) to give the
smooth faces suitable for joinery
(left, above), it is reduced by 3mm
on each face.

It is normal and useful to indicate

in drawings the category of timber
being specified. The graphic
convention for sawn timber, which
is deemed to include the crudely
planed CLS (Canadian Lumber
Size) stud framing, is to draw the
diagonals of the cross-section (top)
and for PAR to suggest the lines of
the wood grain (above).

Timber 161

Composite timbers

Laminated beams

Because the basic rectangular lengths of timber are cut

from a tree trunk, there are, inevitably, off-cuts and other
residual materials, such as sawdust and the thin shavings
created in producing PAR lengths.
Economic incentives have encouraged the
development of composite timber products that utilize
this potential waste material, bonded with specialist
glues, to produce sheet materials that meet specific
requirements within the building industry.
Plywood, MDF, blockboard, chipboard and OSB are
probably the most common timber-based boards. The last
two are produced with an interlocking tongue-and-groove
edge, and are used widely in place of traditional tongueand-groove boards in floor construction. They are less
suitable than timber floorboards as a finished surface but
are superior as a subfloor for tiles and carpets. They are
normally produced in 1220 x 600mm panels, compatible
with the spacing of timber floor joists.

While timber has good structural properties, whether

used as beam or column, its use is limited by both the
natural size of tree trunks from which structural elements
may be cut and the tendency of long lengths to split and
warp over time when exposed to atmospheric variations.
This has led to the development of laminated beams,
which are manufactured from short lengths of timber
glued together and frequently shaped in manufacture
to create structural elements that satisfy both aesthetic
and practical requirements.
CURVED LAMINATED BEAM

LAMINATED BEAM DETAIL

Curved laminated beams

supporting secondary beams
these in turn carry a glazed roof.

This detail of a laminated beam

shows both the individual laminates
that allow the beam to be precisely
shaped during manufacture
and the rich pattern created by
variations in grain and colour.

162 Materials

MDF
MDF (medium density fibreboard) is a board made from
wood fibres glued together under heat and pressure. Its
composition and manufacture make it very stable, with
comparatively hard and very smooth surfaces on its 1220
x 2440mm faces. Readily available thicknesses range from
3mm to 19mm.

Workability MDF has no true grain and can therefore

be cut and machined with great accuracy and without
surface damage. This simplifies the making of sharp
precise angle cuts, or mitres, for the production of
seamless corners, which can be glued and reinforced
with biscuits (see page 132) or dowels.
Although it is heavier than other wood-based
building boards, MDFs workability and stability give
it significant advantages over plywood, blockboard,
chipboard and OSB (oriented strand board) for the on- or
off-site manufacture of furniture pieces and wall panels.
It is also used increasingly to produce simple moulded
elements like skirtings and architraves.
Finishing MDF faces are a good base for paint, but the
softer core, which is exposed on all four edges, is more
absorbent and should be filled, sealed or lipped to provide
a non-porous surface that will ensure a colour tone
consistent with the primary faces. While MDF does not
REPLACING TIMBER
MOULDINGS
MDF is used to produce skirting
mouldings that are more
consistently stable than timber
equivalents, although their edges
are more easily damaged. They
are supplied ready-primed for final
painting. The green core indicates
a waterproofing to withstand
dampness at floor level.

REPLACING PLASTER
The smooth surface of MDF
makes it suitable for comparatively
delicately scaled work. This
example of an internal window
shows how a simple mitred
frame can be pre-fabricated with
great precision. If painted the
same colour as the wall, it will be
indistinguishable from the plaster.

have a strong surface grain, a clear sealant coat will bring

out a rich ginger tone with a slight, lighter fleck pattern.
It also provides a stable base for veneers and laminates.

Specialist boards There are numerous specialist varieties

of MDF. Waterproof sheets are coloured green and fireresistant sheets are pink. Some manufacturers are now
producing decorative coloured boards that are pigmented
through their whole thickness. Others produce sheets
grooved on one side so that they bend easily and evenly.

Disadvantages The density of the board means that it is

necessary to pre-drill screw holes. Nailing is difficult and
can cause the material to split, particularly if the nail is
too near the edge of the board. Nails and screws should
be at least 25mm from the edge. Edges can also crumble
under impact.
It is, however, in the machining and construction
process that the greatest problem with MDF occurs. It
contains urea formaldehyde, which is released during
cutting and sanding and can damage eyes and lungs.
Working areas, whether in workshops or on site, need to
be well ventilated, and masks and goggles should always
be worn. Urea formaldehyde will continue to be released
throughout the life of the product, so it is important to
paint or varnish all surfaces to create a containing seal.

Plywood 163

Plywood
Plywood consists of thin veneers of timber glued together,
with the grain of each layer running at right angles
to those next to it. This means that the tendency of
individual veneers to bend in response to environmental
conditions is neutralized, and the resulting product is a
very stable board.

Manufacture The manufacturing process involves logs

being stripped of their bark and subjected to steam and
hot water to improve their peel quality. Peeling is the
process in which a continuous sheet of veneer is cut
from the rotating log before being oven dried. Varying
numbers of veneers are glued together to produce
differing thicknesses of boards, and the glue is dried or
cured in a hot press. After pressing, the panels are cut
into standard 1220 x 2440mm sheets and graded.
Performance Grading identifies the performance
capability of each sheet. Generally, the better the quality

of the original timber the thinner the individual veneers

and the better the quality of plywood.
Cheaper boards have little graining on their facing
veneers and comparatively thick core layers. This is
because they are produced from the fastest-growing
wood, and the blade peeling the log slices few of the
widely spaced growth rings. Cheap boards are only
suitable for carcassing and temporary constructions,
suchas the shuttering moulds for poured concrete.
Good-quality plywood has thin, dense veneers and
their edges have a clearly defined linear pattern, which
is good enough to be exposed as a finished edge.

Workability and finishing Plywood is relatively easy to

cut, although the extant timber grains in each veneer
mean that the cut edge of the poorer-quality boards may
fray. When plywood is used as a finished surface, staining
will enhance its grain pattern. Even a clear stain will
darken its natural colour.
PLYWOOD VENEERS
Good-quality plywood has multiple
layers of thin ply, which have a
decorative quality and work well
on a mitred corner.

VENEERS
A small selection of high-quality
timber veneers.

164 Materials

Plasterboard
Plasterboard consists of a core of gypsum contained
between two sheets of stiff paper. One side, the back,
is coloured grey. The other, coloured cream, may be
finished with a skim coat of 3mm plaster or, in drywall
construction, painted directly, once its joints and fixing
points have been filled and sanded. The long edges of the
cream face are often tapered to create a recess that can
both receive filler and facilitate levelling during sanding
(see pages 27 and 32).

Sizing Plasterboard comes in a number of sizes: 1200 x

2400mm is the standard, but 1200 x 1800mm and 1200
x 900mm are also common. The smaller sizes are better
suited for work in confined spaces or for single operatives.
Although 1200 x 3000mm can be obtained for taller
spaces, the dimensions of the standard 1200 x 2400mm
sheet are an important factor in determining the most
economical ceiling heights and plan dimensions in new
interiors, particularly in cellular layouts where reduction
of waste in repetitious elements brings significant
economies.

Specialist boards Colour-coded specialist boards

with increased performance are available for specific
applications. A green face identifies improved moisture
resistance; yellow indicates better impact resistance; red

a higher level of fire resistance; and blue indicates

increased sound reduction. Other specialist boards,
usually used for lining external walls, have foam
insulation and vapour barriers glued to their backs.

Workability The comparative softness of the gypsum

core allows the sheets to be cut to size with a handsaw.
However, this can damage the gypsum, which is brittle
and can disintegrate, making jointing particularly in
drywall construction more difficult.
It is therefore more effective to cut the sheet using
a specialist trimming knife and a metal straight edge. An
incision through the paper into the gypsum provides a
weakened line that may be snapped by bending backwards
along the cut, giving a clean break through the gypsum;
the paper surface on the reverse may then be cut.

Loadings When sheets are securely fixed with nails or

screws at 150mm centres they will be robust enough to
deal with significant impact and to support substantial
loadings, such as shelves and cabinets. Where possible,
fixings should go directly into vertical studs. Where this is
not practical because of the dimensions of the supported
element, a screw/plug ideally metal, with a raised thread
that cuts precisely into the gypsum core to produce a
tight connection will be enough for most loads.
PROTECTING EDGES
External corners in plasterboard
construction require reinforcing
with expanded metal beads.
These, nailed to the stud frame,
provide a straight impact-resistant
edge against which the skim coat
of plaster may be finished.

BOARD COMPOSITION
Plasterboard consists of a
brittle core of gypsum plaster
sandwiched between two sheets
of paper.

Aluminium 165

Steel

Aluminium

Steel can be cut with mechanical hacksaws and curved

by rolling between formers. This makes it a particularly
suitable material for complicated edge-beam conditions.
There are a number of types of steel used in the
construction of interiors.

Aluminium is a particularly light and durable metal, and

capable of fulfilling a structural role. It is, however, more
expensive than steel and its use as a structural element in
building is limited. However, with a density around onethird that of steel, it is extensively used for lightweight
framing and as a finishing material. It is protected from
corrosion by the thin surface layer of aluminium oxide
that forms when it is exposed to air.

Mild steel This is obtainable in a number of hot- and

cold-rolled sections, whose three-dimensional profiles
enhance their structural capacity, and is primarily used in
the construction of skeleton structures. Sections may be
welded or bolted together. The latter technique, in which
holes for the bolts are pre-drilled before the sections are
brought to site, while not as strong as welding, allows for
some adjustment in situ.

Stainless steel For smaller steel elements, which are

visible in detailing, stainless steel (an alloy with a
minimum of 10 per cent chromium content) can be
used. It is resistant to rust but can still suffer a degree of
corrosion. It is produced with a range of surface qualities.

Workability Its comparative malleability makes it easy

to machine. It is frequently extruded into profiles similar
to those for steel, but miniaturized for its more modest
structural obligations. Because of its workability and
lightness it can be rolled to produce thin laminates that
may be glued to timber composite boards for rigidity. It is
easily formed using a cold-pressing process, so thin sheets
may be stiffened by folding. One of the most common
applications of this is framing components for drywall
construction. Its lightness makes handling easier.

Finishing In its natural state aluminium is similar to the

Alternative protections against rusting Painting
provides the simplest way of protecting steel. Other more
complex techniques, such as galvanizing with a film of
zinc and other reactive coatings, provide more permanent
protection. Chrome coating of mild steel, which is
applied by an electroplating process, provides a highly
reflective, corrosion-resistant surface.

silvery grey of steel, with variations caused by relative

roughness of surface. It may be coloured, usually by a
powder-coating process in which powdered pigment is
applied electrostatically and heat cured to create an even
skin that is tougher than conventional paints.

Recycling It may be recycled easily and economically

without losing its inherent qualities. This requiresonly
five per cent of the energy used to process raw,natural ore.
Recycled material, described as secondary aluminium, is
used extensively in the production of extrusions.

ALUMINIUM STUD FRAMING

ALUMINIUM STOPS AND BEADS

PRE-FABRICATED ALUMINIUM

The very thin, very light sheet of

aluminium is folded to increase
strength and rigidity in framing for
plasterboard partitions.

Expanded aluminium sections are

vital components in the plastering
process, here providing a stop
bead for three-coat work.

Aluminium is used extensively in

the production of furniture.

166 Materials

Glass
Manufacturing clear float glass
Made using the modern method dating from as late as
1959, which produced clear glass without distortion of
vision or reflection, clear float glass superseded plate
and sheet production (although these two terms are still
used to describe high-quality and thin glass respectively).
In the manufacturing process, molten glass is
poured on to a bed of molten tin, on which it floats and
spreads out to form level surfaces on each of its sides. It
is annealed (hardened) by precisely controlled cooling,
and has almost perfectly parallel surfaces that eliminate
visual distortion. Clear float glass can be manufactured
in thicknesses from 2mm to 25mm, but for building
purposes it is normally restricted to 3, 4, 5, 6, 8, 10 and
12mm with a maximum sheet size of 3180 x 6000mm.
Thicknesses of 15, 19 and 25mm are restricted to sheets
3180 x 4600mm.
Green, grey, blue and bronze colours can be created
by variations in the proportions of ingredients used in
manufacture, which result in selective absorption of
parts of the light spectrum. However, since changing
the proportions of the basic composition of a glass mix
is a lengthy operation, modifications to basic clear glass
are usually produced by surface coatings applied during
manufacture (on line) or afterwards (off line).

Secondary manufacture
Glass can be further modified during what is known
as secondary manufacture to produce different
specifications. These include:

Toughened glass This is made by heating and rapidly

cooling glass after primary manufacture. The process
makes it four times stronger, and better able to deal
with impact, loading or thermal stress. When broken it
disintegrates into small, smooth-edged fragments, making
it particularly useful for glazed doors and screens.
It cannot be cut or worked after manufacture as any
modification to the coherent compressive strength of its
surface will cause it to fracture. Edges must be refined
before the toughening process is carried out, and the size
and possible positions for drilling holes are limited.
The maximum size of toughened sheets is restricted
to 4200 x 2400mm for those produced in a horizontal
furnace and 3500 x 2500mm in a vertical furnace;
thicknesses range from 4 to 19mm. A variety of types
including tinted, reflective and patterned may be
toughened.

Laminated glass This comprises sheets of glass bonded

together with layers of clear plastic to which the glass

adheres when broken, providing a significant safety
factor. Varying thicknesses of the plastic interlayer can
provide protection against physical attack from hammers,
bullets and bombs. It can also improve sound insulation
by dampening higher frequencies.
There are two principal manufacturing methods.
In PVB laminating, a sandwich of polyvinyl butyral is
heat-bonded in an autoclave between sheets of clear
glass. Sheet sizes can be up to 5000 x 2500mm. In
resin-lamination, an edge tape forms a space between
two sheets of clear glass, which is then filled with liquid
resin until all air is expelled. The resin sets to form a
rigid interlayer, the thickness of which can be varied
from 0.38mm to more than 6mm and the number
of laminations from 3-ply (giving 4.4mm thickness)
to 25-ply or more. Patterns printed on to glass can be
protected within the laminations.

Multiple glazing This refers to hermetically sealed units,

where panes of glass are bonded to create a single panel.
Panes are separated by a hollow tube, usually aluminium,
and filled with desiccant to keep the cavity dry. The
sealed edge allows some slight movement of the glass
sheets to prevent cracking, but will exclude moisture
from the cavity. Most thicknesses and types of glass can
be incorporated into multiple units, and the cavities can
vary from 6 to 20mm.
While such units are principally used for thermal
insulation they can also improve sound insulation, and
with the appropriate combination of glass thickness and
cavity gases can attain a reduction of 40 decibels.

Fire-rated glass The fire resistance of some glasses

is greatly increased by their chemical makeup or, in
laminated glass, by the introduction of an intumescent
gel between the glass sheets.
Wired glass This is produced by embedding wire
within the thickness of glass (usually 6 or 7mm) during
manufacture. It is very effective for fire resistance and
security in door panels and screens, as the wire sustains
the glasss integrity. Periods of 90 minutes fire resistance
can be achieved in panels that are up to one square metre
in area.
Glass blocks These are essentially transparent or
translucent components that are bonded with mortar
joints to create a wall or part of a wall. They are hollow
and hermetically sealed and have good acoustic and

Acrylic 167

Acrylic
thermal properties. Their thickness and the consequences
of the manufacturing process mean that, even with
transparent examples, there will be considerable visual
distortion. There is a good range of sizes: 80mm-wide
blocks are 115 x 115mm, 190 x 190mm, 240 x 115mm or
240 x 240mm. The 300mm-square block is 100mm wide.

Curved glass Curves are created by placing flat glass on

top of a metal mould or refractory inside a kiln, which
is heated until the glass softens, sags and takes on the
shape of the mould. The kiln is cooled slowly for between
12 and 24 hours to avoid stressing the glass. Normally the
maximum sheet size is 3000 x 2500mm. Toughened and
laminated glass can also be bent.

Decorative finishes
Sandblasting The surface of clear glass is pitted by sand
particles hitting it at high pressure. Areas of the surface
may be masked off to allow varying degrees of intensity
of pitting or to create tonal patterns, or protected wholly
to leave transparent areas. The process is not easy to
control and works better if fine detail is avoided.
Acid etching This technique allows much greater
control than sandblasting and is better suited to finely
detailed decoration. The surface of the glass is eroded by
hydrofluoric acid to produce degrees of translucency.

Brilliant cutting Patterns are cut into the thickness of the

glass and edges are smoothed and polished. The facets
exploit the effect of light.

Transparent, translucent and opaque plastic sheets can

offer more practical, and sometimes more economical,
alternatives to glass; the most common of these is acrylic.
While trade names, such as Perspex and Plexiglas, are
in common use, it is perhaps better to use the generic
label since these, and all similar products, are derived
from acrylic acid. While their cost may make them
impractical as an alternative to float glass in conventional
applications, when specialist glasses are required acrylicbased products are often viable.

Manufacturing methods There are two main methods.

Extruded, or continuous-cast, production is less expensive
but the material is softer, more easily scratched and
contains impurities that affect strength. Cell cast is more
expensive but better quality and more reliable. The
standard clear sheet may be coloured by the addition
of dyes during manufacture.

Properties Acrylics transparency rating of 92 per cent,

with a 3mm thickness, makes it the clearest material
available and it remains clear regardless of its thickness,
while glass will develop a green tint as thickness
increases. In addition, acrylic products do not turn
yellow, become brittle or fracture with age.
It is significantly stronger than unreinforced glass,
with a high resistance to impact damage. It has better
insulative properties than standard glass and is less than
half its weight. This, with its less brittle character, makes
it easier to work. It will not shatter but will break into
large pieces without sharp edges. It can be cut with a saw
and easily drilled to receive screws.

Opal glass A pre-finished decorative glass, available in

white, coloured or variegated form and ranging from a
translucent white or flashed opal to opaque or pot opal.

Cutting and shaping glass

While all glass, except toughened, can be cut after
production, it is not recommended that this be done
on site for any but the simplest operations.
For comparatively simple straight-line cuts
information on dimensioned drawings will be sufficient
for scoring, but for curves and irregular shapes a template
is needed to guide the cutting tool.
Acute internal corners should be avoided where
possible because they represent points of weakness.
If they are unavoidable, a radiused corner, as large as
possible, should be incorporated into the angle. The
centre of any drilled holes should be at least four times
as far from the edge as the thickness of the glass.

Applications Acrylic is particularly useful because it is

easy to bend and therefore better than glass for curved
screens. Although it is softer than glass and therefore
more susceptible to scratching, marks may be removed
by polishing or surface heating.
It is particularly useful for display and exhibition
cabinets. It has a low reflectivity and its inherent strength
and flexibility copes with viewers leaning on it. Resistance
to impact also means that it is more secure than cheaper
forms of glass. It can be easily shaped, and components
can be joined by heat or solvents. It dissolves at the joint,
fuses and sets, forming an almost invisible weld.

168 Materials

Fixings
Gluing

Types of nail

The options for fixing the basic materials used in interior

construction are simple. They are nailing, screwing or
gluing. The last is becoming more popular, particularly in
carpentry and joinery work, since adhesives specifically
designed to replace nails and screws have become
more efficient and widely available. Gluing provides an
invisible fixing but rules out the possibility of future
disassembly and recycling, and there are difficulties in
most existing buildings where surfaces are uneven and
an even spread of the adhesive is impossible. A good
glued joint will, however, be stronger than the timbers it
connects so that if the joint fractures it will be because of
a failure in the wood, which will split first under stress.

Round wire These are used for carpentry work and can

Nails
When nails are hammered into timber they are forced
between the wood fibres, which close back and grip them.
They are the least strong of joining options, but are also
the most common as they are simple and fast to use.
There is a wide range of types, covering the specialist
requirements of carpentry and joinery. They normally
remain visible, although their heads may be driven
below the surface of timber using a nail punch, a small
chisel-like tool with a flat, round head that transfers the
impact of a hammer to the nail head without damaging
the wood. The small indentation created will disappear
if filled with a specialist compound, sanded and painted.
Electric nail guns are significantly faster than the
handheld hammer. They require special nails, but speed of
operation more than compensates for a modest extra cost.

vary in length from 15 to 200mm. The round head

remains visible after fixing.

Oval wire From 20 to 150mm long, these have oval heads

that may be driven a little below the timber surface,
which is useful when other elements are to be fixed flat
against the nailed surface.

Lost head These are from 15 to 75mm long and may be

driven easily below the timber surface, the indentation
filled and sanded for an invisible repair.
Panel pins From 10 to 75mm long and very thin, these
are used for fixing thin board materials to framing and
for the initial securing of joints while glue sets. The small
heads have little visible presence against wood grains and
are also easily driven below the surface of timber, with
the subsequent indentation filled, sanded and painted.

Clout These, from 15 to 50mm long, are used to fix

plasterboard sheets to timber stud framing. The large
heads effectively clamp brittle plasterboard by spreading
the connection. The head sits on the surface of the board
but is covered by the final 3mm skim coat. The nails
are galvanized to prevent rusting, which would cause
swelling of the nail and damage the plaster.

CARPENTRY NAILS (FAR LEFT)

The round-headed nail is on the
left. The head of the oval, on the
right, can be hammered below the
surface of the wood.

PLASTERBOARD FIXINGS (LEFT)

Galvanized clout nails, on the
left, secure plasterboard sheets
to be finished with skim coat.
Large heads increase the point
of contact. The countersunk
plasterboard screw on the right
fixes plasterboard sheets for
drywall construction. The head
is sunk below the surface of the
board and the indentation filled
and sanded before painting.

Fixings 169

Screws

Countersunk The head of a countersunk screw, which

The raised thread that distinguishes screws from nails

is designed to cut into timber, so that the thread ridges
are integrated into, and locked in position by, the
wood that surrounds them. Screws, therefore, provide a
more secure connection than nails and are more easily
removed, although they do leave holes. Battery-powered
screwdrivers and drills make the use of screws simpler and
faster. Pre-drilling, with a bit diameter smaller than that
of the screw, will speed the process and reduce surface
damage.

tapers towards the shaft, can usually be screwed tight

enough to finish flush with the surface of the timber or
board it is securing. It is possible to ensure a wholly flush
finish by making an inverted cone-shaped recess in the
timber surface, using a countersinking bit. This will also
eliminate the possibility of damage to the wood surface as
the screw is forced home. A screw cup inserted over the
shaft before fixing will also limit damage and provide a
positive visual transition between screw and wood.

Types of screw
There is an extensive selection for use with different
types of material and in different conditions. Some are
purely utilitarian but others are intended to make a
positive visual contribution. All are classified by size: shaft
thickness, length, material and type of head (for example:
size 6, 50mm, steel countersunk). The greater the size,
the thicker the shaft and therefore the stronger the screw.

Round-headed or dome-headed The heads of these

screws, which have a flat underside that finishes tight to
the surface of the wood, sit on top of the wood and will
cover minor damage caused in the fixing. A washer under
the screw head will cover local damage.
Self-tapping This is a screw with a hard, sharp thread
that can cut into and find a secure grip in thin metal.
Its most common use in construction is with metal-stud
framing where the screws are also coated to prevent rust.

Nuts and bolts

Bolts, like screws, are threaded, but have a flat rather
than a pointed end and wholly penetrate through predrilled holes in the elements they are connecting. They
are secured with a threaded nut on the reverse side. They
are used in a wide range of applications: large diameter
and heavy examples are utilized to connect structural
elements; smaller, lighter sections are used to fix metal
glazing beads. Pre-drilled holes normally have a slightly
bigger diameter than the bolt to allow some tolerance
for fixing, and washers that fit neatly over the bolt cover
the gaps that are left. When timbers are bolted, washers
spread the load and prevent the head of the bolt and the
nut biting into the softer surface of the wood.

NUT, BOLT AND WASHER

The washers cover the edges of the
pre-drilled hole made for the bolt
and spread the load of both the
nut and bolt over the surface of
the material being secured.

CHAPTER 10 STRUCTURAL
PRINCIPLES

172 INTRODUCTION
172 MATERIALS IN COMPRESSION AND TENSION
174 ORIENTATION OF STRUCTURAL ELEMENTS
176 CANTILEVERS
177 BEAMS
178 STABILITY
180 RULE-OF-THUMB SIZING

172 Structural principles

Introduction

Materials in compression
and tension

Interior-design projects seldom involve building

significant new structures or major additions or
amendments to existing buildings. When these do
prove necessary, it always makes sense to have properly
qualified engineering advice to ensure the most effective
solution and to provide the calculations necessary to
gain approval from local authorities, whose minimum
standards tend to be demanding, with very conservative
estimates given for the structural capacity of materials.
The loadbearing capacity of existing elements
can become a crucial consideration when a building is
adapted, particularly for a change of use. Regulations
may decree that old walls and joists are insufficient to
meet modern requirements for offices or restaurants,
potentially making any project economically
unacceptable. Removing existing elements, particularly
floors and beams, may affect the stability of a structure
by reducing their bracing effect on walls. New loadings,
especially on elements like columns that have little
inherent lateral strength, may create unacceptable
stresses that will lead to structural failure.
It is still useful to have a knowledge of basic
principles so that initial design work is realistic and will
not need to be amended too dramatically or destructively
when an engineer suggests final strategies. Knowledge
of principles also allows a designer the only person
with a comprehensive vision of the project to discuss
and assess options realistically and point in a viable, and
aesthetically acceptable, direction that an engineer, with
a necessarily restricted perspective, may not see. While
the structural guidelines here are discussed in relation to
major structural work, the principles also apply to smallerscale detailing.

All structural members walls, columns, beams and floor

and ceiling slabs are in compression or tension or both,
depending on their role and location. When elements
under compression fail, they fracture and disintegrate.
They are usually comparatively bulky, to spread the
imposed load over a bigger area and counteract bending.
When elements under tension fail, they tear apart.
However, these elements can be very thin since they do
not have to resist bending.

LOAD

COMPRESSI
COMPRESSTI
COMPRESSTIOONNON

WALL UNDER
COMPRESSION

TENSION

This occurs when a supporting

element, such as a suspension
cable, is stretched by the load
it carries.

LOAD

TENSI0N

COMPRESSTION

This occurs when a supporting

element is compacted by the
weight of the load it carries,
such as a column resting on a
firm foundation and carrying the
weight of a floor above.

COMPRESSTION

COMPRESSION

COMPRESSTION

SUSPENSION
WIRE UNDER TENSION

T
E
N
S
I
O
N

Materials in compression and tension 173

Structural materials

Most structural members, even those only supporting

their own weight, are subjected to both compressive
and tensile forces. The clearest example of this is a
horizontal beam spanning between columns or walls.
The tendency of the beam to bend under loading means
that the material on the upper edge will be compressed
and the material on the lower edge will be tensioned. The
intensity of both effects lessens towards the centre of the
beams cross-section, with the forces exerted in the exact
centre neutralized. It is therefore good practice to make
holes for the passage of services in the centre of beams.

Timber The comparative lightness of timber and the

LOAD

ease with which it may be cut and fixed make it the first
choice for most structural work. It functions well in both
compression and tension. Lengths of timber are cut so
that fibres run lengthwise, providing structural continuity.
In its simplest form, with a rectangular section,
timber is quite adequate for floor and ceiling joists and
for framing walls. Composite beams may be constructed
using timber-based sheet materials for depth, and natural
timber lengths for lateral rigidity. Laminate beams, which
are composed of glued strips of timber, can rival steel and
concrete for strength and, although they are liable to be
greater in cross-section, are easily bent and curved.
TENSI0N

COMPRESSTION

The combination of forces

Steel While excellent in tension, steel is comparatively

LOAD
STRUCTURAL BEAM
COMPRESSION

TENSION

FORCES IN BEAMS
When a beam supports a load its
top edge is in compression and the
bottom in tension.
LOAD

RESISTANCE TO BENDING
A column in which the dimension
of one side is significantly greater
than the other is liable to buckle
under loading, even when that
loading does not exceed the
nominal capacity of the material
used in the columns construction.
The tendency towards buckling
varies with material, but with all
types this can be counteracted
by an increase in the shorter
dimension (which will also
decrease the longer, since the
cross-sectional area will remain
constant).

poor in compression. However, it is malleable during

manufacturing and is produced in a number of standard
sections that counteract its tendency to bend under
compression. The profiles, of which the best known
are I, L and C sections, reduce the volume of steel
required while decreasing the width-to-depth ratio to
increase lateral rigidity.
The loadbearing capability of each available section
is set out in tables produced by the bodies responsible for
approving structural work. These take into account not
only dimensions but also the thickness of metal used. This
gives scope for varying dimensions to suit site conditions.
Thicker cross-sections will allow smaller dimensions.

Concrete While extremely strong in compression,

concrete is very weak in tension. Except when supported
over its entire area, as in ground-level floors, it must be
reinforced with steel rods or mesh, positioned in the
mould into which the wet concrete will be poured,
and if covered to a depth of 50mm, it will be protected
against rusting, which would cause steel to swell and
fracture the concrete.
It is interesting, perhaps remarkable, that the thermal
expansion rates of concrete and steel are the same, so
both expand and contract at the same rate. Differential
movement would result in fracturing.
Masonry Brickwork, blockwork and stone all function
primarily as supporting elements. Shallow arches,
supported on wooden or metal formwork while the
mortar sets, can be an alternative to steel or concrete
lintels, but are complicated to construct and inevitably
have curved profiles, so are primarily used for decoration.

COM
174 Structural principles

Orientation of structural
elements

BEAM

WALL

TENSI0N

COMPRESSTION

Generally, the greater the size of a structural member, the

stronger it will be, but for economical, and sustainable,
solutions, the less material used the better. The
calculation of the most efficient solution depends on
finding the optimum relationship between the depth and
width of structural elements. The strength of a beam or
column is crucially affected by the relation between its
longer and shorter dimensions.
Any element whether a beam, slab or column
will be weakest at its midpoint because the effect of the
load will be greatest and there will be less support against
bending and distortion from lateral restraints.
While the depth of a beam, on the vertical X-axis,
will principally determine its loadbearing capacity,
its width, on the horizontal Y-axis, will determine its
stability when loaded. In a beam the X dimension
will normally be greater than the Y, but this has less
significance in the design of an evenly loaded column,
when there will be no variation in stresses over the crosssectional area. Square and rectangular cross-sections will
work equally efficiently.

LOAD

BEAM
LOAD

WALL

DEPTH AND WIDTH

ORIENTATION AND LOADING

The loadbearing capacity depends

on depth (X) while stability
depends on width (Y).

The depth of a material relates

directly to its performance, and
the same cross-section of the
same material will perform quite
differently if laid with its greater
dimension horizontal (1) than
vertical (2). Whether it is a beam,
slab or column, it will be weakest
at itsmidpoint.

Orientation of structural elements 175

The basic principles of creating a viable structure

are simple, and most people will have an instinctive
understanding of how they work. This knowledge,
coupled with learning and experience, can suggest
structural configurations that fulfil their functional
obligations efficiently but also deliver a visual impact.

Depth and strength

The depth of a beam is the crucial factor in combating
failure caused by loading. Greater depth relates directly
to greater strength, but lateral distortion can occur when
a beam does not have sufficient width to resist buckling

under loading. As long as the structural component can

withstand such lateral distortion, it is more economical
(and sustainable) to reduce the volume of material used
in manufacture when possible.
depth and loading
1 Lateral distortion: a beam needs
width to resist buckling.
2 Rolled steel joist (RSJ) the
horizontal flanges in this, the
most common steel profile, resist
lateral movement in the web (the
vertical element of the joist).

LOAD

Increased depth at the

midpoint
The profile of a beam may be
shaped in response to the forces
acting within it, with greater depth
at its midpoint. The resulting
triangular profile will be equally
effective as a roof structure, with
its apex above the points of
support (1), or as a beam for long
floor spans, with its apex below
support points (2).

3 To reduce the use of materials,

holes may be cut from the web
without affecting the strength
that is gained from its depth.
The holes facilitate the distribution
of services.
4 Hollow box beam: composite
timber board provides depth and
lateral rigidity; lengths of natural
timber reinforce glued joints.
5 I-section timber beam:
composite timber board provides
depth, and lengths of natural
timber provide lateral rigidity.

176 Structural principles

Cantilevers
A cantilever is a projecting horizontal element, usually
a floor or canopy. It fulfils practical functions but is
generally an aesthetic gesture.

Simple cantilevers It is feasible to attach a modest

projecting element from a wall or line of columns if a
sufficiently substantial connection can be made. The
further a cantilever projects beyond its support point,
the greater the strain on both the connection and the
supporting element. It is unlikely that anything in
excess of a metre is viable. Additional connection to a
supporting structure can be provided by an angled strut
in compression below the cantilevered element, or a tie in
tension above it, so that loading on the front edge of the
cantilever is transferred back to the supporting structure.
The latter may be incorporated into a balustrade.

CANTILEVER

TENSION
COMPRESSION

Counterbalanced structures For more substantial

cantilevers it is more effective to build a counterbalanced
element in which a conventionally supported structure,
whether timber joists or a concrete slab, is projected
beyond one of its support points. The greater weight of
the conventionally supported area should be sufficient to
stabilize the cantilevered section. The counterbalancing
effect can be increased by additional loading on the noncantilevered section of a floor structure.

Tapering It is common practice to taper the underside

of a cantilevered floor: since the area of the projection
is normally less than that of the floor from which it
extends, its depth can be less. The taper will emphasize
the lightness of the cantilever and suggest visually that
it is braced against the supporting structure. The angle
of taper may be exaggerated visually.

CANTILEVER

SHIFTING FORCES
For the area of the slab that is
conventionally supported on the
walls, the top edge will be in
compression and the bottom in
tension. This will be reversed for
the cantilevered section when the
top is in tension and the bottom
in compression.

TAPERING CANTILEVERS
A cantilevered beam or slab
may be tapered away from the
supporting point, allowing the
depth of the beam or slab over
the cantilever to be reduced, as
it carries less weight.

CANTILEVER

STRUCTURE WITH
COUNTERBALANCING WALL
As long as the weight of
the cantilevered element is
exceeded by the weight that is
counterbalancing it, then the
structure should remain stable.

Beams 177

Beams
Disguising beams

Alternative beam sections

Downstand beam A conventional downstand beam

While the rectangle remains the most common crosssection, there is no reason other than cost and possible
delays in the manufacture that other options may not
be used.

projects below the floor it supports, so it is a visually

significant element in the rooms below, unless concealed
by a suspended ceiling. With restrictive floor-to-floor
heights there may not be the headroom to accommodate
it, although a height of 2000mm to its underside, or to
the underside of the suspended ceiling that covers it, will
usually be acceptable immediately underneath.

Upstand beam It is possible to introduce an upstand

beam, projecting above the floor it supports. This would
have to be accommodated within a wall in the rooms
into which it projects, or alternatively by a change of
level, if it is not to form an obstruction. An upstand
beam may also be contained within the thickness of
a balustrade on the edge of a mezzanine floor.

Mezzanines It is also feasible to design a lightweight steel

edge beam that will both support the edge of a floor and
provide a handrail for the mezzanine.

Circles A circular steel section is reasonably easy to

obtain. However, for clear expression of the purity of
the circular section, the beam and the floor slab should
be separated visually by spacing cleats. An oval beam
provides a section that responds more closely to structural
width-to-depth ratios.
Triangle It is possible to produce a beam that has three
solid faces, but it is more usual to exploit the inherent
strength of a triangulated structure by reducing it to a
skeleton of members in compression and tension. It may
be used with the flat surface at the top or bottom. The
latter has the advantage of visually separating the beam
and the supported floor slab.

DISGUISING BEAMS
1 Downstand beam projecting
beneath floor.
2 Upstand beam absorbed in the
wall above.
3 Upstand beams can act as
balustrades on the edge of bridges
or mezzanines.

ALTERNATIVE SECTIONS
4 Circular beam.
5 Oval beam.
6 Triangular beam.
7 Triangular beam with skeletal
members.

178 Structural principles

Stability
Allowance is frequently made for some limited, controlled
movement in the design of large-scale external structures,
to allow response to short-term temperature and loading
changes. Interior construction tends to be protected
from extreme environmental variations, and loadings are
generally modest. However, the elimination of movement

in interior construction is necessary to prevent damage

to finishes. Construction techniques have evolved to
minimize the amounts of material used and reduce
construction time, and standard practice has adopted
a number of these stratagems to ensure an appropriate
degree of rigidity.

STRUCTURAL INSTABILITY

A frame with simple unreinforced

corner joints that lack inherent
rigidity will tend to distort under
minimal pressure. A single nail
or screw connection will act as
a fulcrum, around which the
connected elements will rotate.
Two or more connections at a
joint position will not eliminate
theproblem because they
will be too close together to
counteract rotation.

STUD PARTITION
The addition of extra vertical
and horizontal members, as in
stud partitions, will reduce the
tendency to distort. While the
individual connections, of single
nails or screws, will not themselves
be rigid, the accumulative effect
of elements within the whole
reduces movement.

2
SKELETAL FRAMING BRACED
BY SHEET MATERIAL
Simple butt joints and fixings
(often the result of economic
priorities) will remain fragile, but a
skeletal structure can be stabilized
if clad with rigid sheet material.
The most common example
is the stud partition, in which
plasterboard sheets are used to
establish and retain right angles.
Plasterboard is not particularly

resistant to impact and is easily

damaged by the nails or screws
fixing it to the studs, but the
frequency of fixing points spreads
the strain evenly over the entire
surface of the frame. The filling of
gaps between sheets with plaster
skim or drywall jointing compound
makes the whole monolithic. The
principles apply regardless of
material.

Stability 179

PARTIAL COVERAGE OF
STRUCTURE
It is not necessary to cover the
whole face of a frame to make it
rigid, although the less area used
for reinforcement, the stronger
the reinforcing material must be
and the more secure the jointing
techniques (4, 5, 6). When
edges of panels are exposed, the

sheeting material must be capable

of withstanding damage to
exposed and unsupported edges.
Examples include composite
timber board like plywood, fixed
with secure screw fixings and glued
to spread the contact surface, or
metal sheets screwed to a timber
frame or welded to a metal frame.

5
TENSION WIRES AND RODS
With a well-engineered and
constructed skeletal frame,
which may be timber but is more
likely to be metal, any distorting
effect may be combated by
crossed tension wires, which will
counteract a tendency to move
in either direction (7). A single
wire can counteract movement
in only one direction and will
tend to destabilize the structure

6
by allowing the distortion of the
frame when tensioning is applied
(8). A single rod that remains rigid
in both compression and tension
will be structurally effective but
have a heavier, more visually
obtrusive section (9). The angles
of the frame to which tensioning
elements are attached must be
strong enough to contain the
stress caused by the tensioning
of the wires.

180 Structural principles

Rule-of-thumb sizing
While final sizes should be calculated by a structural
engineer, it is valuable for the designer to have a realistic
idea about the likely dimensions of structural elements
in the initial stages of project development. This should
ensure that proposals are essentially feasible and do not
have to be abandoned when significant time has already
been devoted to evolving them. The ratios here are rough
guides only.

1 Loadbearing masonry
(brick, block or stone)

3 Reinforced-concrete
columns

T (width) should not exceed

1
12 of H (height).

T (width) should not exceed

1
15 of H (height).

2 Improving stability

4 Steel columns

Piers, or attached columns,

bonded into, and therefore
integral to, a brick wall at regular
intervals effectively increase its
width and therefore its stability.
The same principle applies to
construction in any material.

T (width) should not exceed

1
30 of H (height).

Rule-of-thumb sizing 181

H
H

5 Timber columns or posts

6 Beams

T (width) should not exceed 120

of H (height) this rule of thumb
does, however, vary with the grade
of timber used.

D (depth) should be at least 115

of the span. However, with rigid
braced corners this can be reduced
to 120.

7 Floor slabs SUPPORTED ON

TWO SIDES

8 Floor slabs SUPPORTED ON

Four SIDES

When the floor slab is supported

on two sides, the slab depth
should be 125 of the span.

When the floor slab is supported

on four sides, the slab depth
should be 130 of the span.

SLAB

SLAB

BEAM

BEAM

COLUMN

COLUMN

SLAB
WALL

SLAB
WALL

CHAPTER 11 A TO Z

184 GLOSSARY
188 RESOURCES
190 INDEX
192 PICTURE CREDITS
192 ACKNOWLEDGEMENTS

184 A to Z

GLOSSARY
A
Architrave : A strip usually wood, sometimes metal or plastic, frequently
decoratively moulded that covers the junction of wall and frames for
doors and windows. It may be fixed by nailing, screwing or gluing.
Arris : The sharp edge formed by the meeting of two planes, for instance
a corner.

B
Baluster : The vertical member that supports the handrail in a balustrade
(see below).

Conduits : Metal or plastic tubes square or round in section attached

to the surface or embedded in walls or floors, through which service
elements, usually electrical wiring, are circulated. Wire lies loose and may
be pulled out and replaced without destroying finishes.
Contract : The formal, legal agreement between client and contractor that
specifies the work to be done and the sum for which it will be completed.
Contractor : The individual or, more usually, the company who will carry
out construction. They should have a contractual agreement with the client
to carry out the work described by the designer in tender drawings and
written documents. They may be responsible for all or part of the work
but it is usual for specialized work, such as the installation of heating and
ventilating equipment, to be carried out by subcontractors (see below).

Balustrade : A protective vertical barrier on a stair or mezzanine.

Batch production : Limited production of the same artefact.
Bead : A thin strip of wood, metal or plastic, sometimes decoratively
shaped or moulded, that secures panels or sheets of glass, or provides
cosmetic cover for joints.

Cornice : A strip usually plaster, sometimes timber or plastic, often

decoratively moulded that covers the junction of wall and ceiling. It
may be fixed by nailing, screwing or gluing.
Countersinking : The recessing of screw or nail heads to finish either
flush or a few millimetres below a finished surface to allow filling and
making good.

Biscuit : An elliptical composite-timber sliver inserted into both faces of

a butt joint to improve adhesion.

Course : A single-level stratum in masonry construction.

Blockwork : Masonry constructed with concrete blocks usually plastered,

sometimes left fairfaced.

Cover strip : A strip usually thin timber, frequently decoratively moulded

used to mask raw joints and junctions.

Butt joint : The simplest joint two elements are clamped flat against each
other and secured by nails, screws or adhesives.

D
Dabs : Spots of plaster (75100mm wide) added to an existing wall
to provide adhesion for a plasterboard fixed directly on to the wall,
minimizing making good.

Carcass : The basic structure that supports cladding panels in joinery work.
Carpentry : Structural and framing woodwork, usually using sawn timbers.
A first-fix operation, liable to be encased behind finishing materials.
Chamfer : The angled trimming of an edge to reduce its visual bulk.
Chases : Channels cut in walls or floors to accommodate runs of wiring
or piping and covered after installation.
Clear float glass : Glass, free of distortion or reflection, produced by
pouring molten glass over a bed of molten tin.
Clout : A nail with a large round head, used where the area of contact must
be spread to avoid damaging brittle materials, particularly plasterboard.
CLS : Abbreviation for Canadian Lumber Size, a standard sizing for
roughly finished sawn timber used primarily as framing in stud partitions.
Column : An isolated vertical element circular, square or rectangular in
cross-section usually constructed of concrete, steel or brick, primarily
used to support overhead structures but which can also serve to subdivide
areas, when it may be non-loadbearing and constructed of plasterboard or
plaster and expanded metal lath on a stud frame.

Dead load : The total weight of building components that must be

considered in the calculation of structure.
Door stops : Continuous strips, usually timber, which are nailed, screwed,
glued or integral to the door frames against which the door leaf closes.
They also serve to reduce draughts.
Dowel : A short cylindrical length of timber or of timber-composite
material that is inserted into abutting faces of a timber joint in order
to improve adhesion.
DPC (damp-proof course) : A strip of waterproof material inserted across
the width of a wall, under sills or around door and window openings, to
prevent water penetration to the interior.
DPM (damp-proof membrane) : A sheet of waterproof material laid over
the total area of a floor or wall to prevent water penetration to the interior.
It should be bonded to a damp-proof course to create a complete seal.
Dry-lining : The construction of an inner skin, usually plasterboard on a stud
frame, against a solid outer wall to prevent water penetrating the interior.
Drywall : A method of constructing plasterboard partitions and ceilings
that relies on specialist fixing and filling techniques to eliminate the need
for a finishing skim coat of plaster.

Glossary 185

Expanded metal : A mesh used to support and reinforce plasters and

renders, made by cutting short slits in a flat aluminium or steel-alloy sheet
that is then pulled in two opposing directions so that it distorts to form a
three-dimensional mesh.

Jamb : The vertical edge of a door or window opening.

F
Fairfaced : Masonry construction that is left exposed rather than plastered
or otherwise concealed. It will normally require a more expensive product
and more care and skill in construction to achieve a satisfactory standard.
Finger joints : Metal jointing mechanisms in which projecting fingers
secure adjacent corners of sheets in a glass wall.
First fix : The installation of, primarily, service elements such as plumbing
and electricity that must be carried out before further building work makes
access impossible.
Flange : A flat metal projection or extension formed during manufacture
or added to a primary metal element to strengthen it or to provide a
fixing device.
Flight : A single, unbroken run of stairs or steps.
Framed : A construction that relies on a skeleton structural support to
provide fixing and stability for cladding panels.

G
Galvanize : To coat steel and steel alloys with a zinc alloy to protect
against rusting.

Joinery : Visible finished woodwork, carried out on site but frequently

partly pre-fabricated in workshops, and almost invariably using PAR timber
(see below) and applied as a second fix (see below).

K
Key : A roughening of surface to improve cohesion for applied wet
finishes, principally plaster.

L
Laminated glass : Sheets of glass sandwiched with layers of clear plastic
to which the glass adheres when broken, improving safety.
Landing : The horizontal area between sloping flights of stairs or steps.
Lath : A perforated base to support and reinforce plaster, traditionally
consisting of thin strips of timber and now of expanded metal (see above).
Live loads (also known as superimposed loads) : The total weight
of elements such as equipment, furniture and people that are not
components of a built structure and must be considered in the calculation
of the forces on a structure.
Lost head nail : A nail with a narrow oval head that can be driven below
the surface of timber.

Going : The horizontal length of a flight of stairs, the distance it covers

onplan.

Main contractor : The individual or company responsible for the greater

part of construction on a project and also for liaison with, and support for,
subcontractors (see below) to ensure efficient completion of the contract.

Grout : A fine mortar used to fill joints, particularly between floor and
wall tiles.

Masonry : Bricks, concrete blocks or stones, bonded with mortar.

MDF (medium density fibreboard) : A board made from wood fibres,

glued together under heat and pressure. It may be machined with great
precision.

Hanger : A timber or metal element that connects a suspended element

toits structural support.
Head plate: The horizontal top member in a timber or metal stud partition.
Header : A brick or block built into a wall so that its shorter edge is
exposed.

I
In situ : Work carried out on site.
Intumescent strip : Material, usually recessed into a door frame or door
leaf, that expands in heat to prevent the passage of smoke throughout
a burning building.

Mitre : The angling of the edges of two abutting planes to ensure visual
continuity of surface. The angle of each mitre should be half that of the
angle of the corner.
Monolithic : Being, or appearing to be, constructed solidly of one material.
Mortice and tenon : A traditional joinery joint in which a slot (the mortice)
is cut in one element to receive a compatible projection (the tenon) in the
other. The two elements interlock tightly but the joint is normally glued
for additional cohesion.
Mullion : The vertical framing member in a window or glazed screen.
Multiple production : See batch production.

186 A to Z

N
Nail : A metal pin that, when hammered into timber, forces fibres apart
and is consequently gripped tightly by them as they try to return to their
original state. Nails come in various sizes and cross-sections for various
applications.
Nail punch : A metal device with a small flattened point that, when
struck by a hammer, will drive nail heads below the surface of, usually,
wood or wooden-composite materials, to allow for filling and sanding
before painting.

Plate glass : A term now used primarily to describe high-quality glass but
which originally referred to a manufacturing process.
Point load : A concentration of the weight of a structure, the result of
its being supported by a column or pier, that usually requires increased
foundation provision.
Post : A wooden column, usually loadbearing.
Precast : A description of elements, typically of concrete or plaster, that are
shaped and hardened in a mould before being brought to site. They may
be one-off, batch or multiple production (see above).

Nosing : The projecting front edge of a stair tread.

O
One-off (production) : The making of a unique object.
Opaque : Cannot be seen through and will not allow light to pass
through.
Oriented strand board (OSB; also known as strand board) : Composite
board made up of very thin slivers of wood, glued together under heat
and pressure that is stable and useful in carcassing work.

Pre-fabricated : Refers to work, usually complex or delicate, that is shaped

and assembled in a specialist workshop before being brought to site for
installation.
Production information drawings (also known as production or working
drawings) : Drawings made by a designer to instruct contractors (see
above) and subcontractors (see below) about the extent and quality of
work necessary to complete a project satisfactorily. Such drawings should
be comprehensively annotated with dimensions, descriptions of materials
and assembly methods.

Oval wire nail : A nail with an oval cross-sectioned shaft and a slightly
wider oval head that may be driven below the surface of timber.

Pugging : Loose material stone chippings, sand or clinker laid between

joists to improve sound insulation by reducing reverberation and the
passage of sound waves across voids.

Packing out : The insertion of timber slivers in localized gaps between new
and existing elements to ensure a firm connection.

Rise : The vertical height of a flight of stairs or steps.

Padstone : A beam usually reinforced concrete, but which may also be

stone or steel built into a masonry wall to spread the weight of a point
load (see below).
Panel pin : A very thin, usually short, nail used for fixing sheet materials
to a supporting frame. The small head may be driven below the surface
of the sheet.
PAR : An abbreviation of planed all round, describing timber that has
had an average of 3mm planed from all faces of its sawn lengths. It is
used primarily in joinery work.
Partition : An internal wall, usually non-loadbearing and of lightweight
stud framing and plasterboard construction.
Patina : The patterning or discolouring, usually accepted as decorative,
that occurs when a material is subjected to ageing, weathering or both.
Some effects may be artificially induced.
Permissible loading : The weight that a building element or material is
designated capable of supporting by the statutory body responsible for
approving building work.
Pier : A projection beyond the face of a wall to provide lateral bracing or
support for a point load.
Plaster beads and stops : Expanded metal strips used as guides
during plastering and as reinforcement for vulnerable plaster edges
and angles. There are various profiles to suit various locations and
plastering techniques.

Riser : The vertical element in a step.

Round wire nail : A nail with a circular cross-sectioned shaft and a wider
circular head that finishes on the surface of timber.
Routing : The mechanical cutting of a channel into timber or timber-based
boards to improve joint adhesion.

S
Sawn timber : Lengths of timber with the rough finish that results from
the initial conversion of tree trunk to plank, used primarily in carpentry.
Screed : The smooth and level final coat on a concrete floor. It may be
used as a finish in its own right or to provide a substratum for thin floor
finishes.
Screw : A pointed fixing device with a raised thread or continuous helical
ridge, which, when turned by a hand or electrically powered screwdriver,
cuts into a material, usually wood, so that the areas between the threads
are filled with the material, creating a fully integrated connection.
This interlocking makes screws significantly more effective as a gripping
device than nails.
Screw cups : Raised circular metal collar for a screw, raising it slightly
from the surface of the fixed element and masking any surface damage
caused during fixing.
Scrim tape : A loosely woven jute fabric or paper strip used to bridge, and
reinforce, joints in plasterboard construction.

Glossary 187

Second fix : Final installation, primarily of fixtures and fittings, after

building work has been effectively completed and further incidental
damage is unlikely.
Self-tapping screws : Screws with a sharp raised thread, which penetrate
and connect thin metal materials.
Shadow gap : The, usually narrow, space created by the physical
separation of elements, which, in modern construction and assembly,
replaces the traditional cover strip as a device for visually refining joints.
Sheet glass : Refers to thin sheets of glass.
Shuttering : A temporary mould for concrete during pouring and drying.
Skim : The final coat of plaster on a wall or ceiling, approximately 3mm
thick, which is polished to give a smooth surface. It may be applied
to one or two undercoats on a masonry wall or as a single coat on
plasterboard. It is usually finished with paint or paper.
Skirting : A strip usually wood, sometimes metal or plastic frequently
decoratively moulded, that covers the junction of wall and floor. It is fixed
by nailing, screwing or gluing.
Soffit : The visible underside of major elements such as floors and stair
flights.

Tender drawings : These usually comprise the complete set of production

information drawings, but it is possible to seek tenders on the basis of a
representative selection of key drawings. This is acceptable as long as all
contractors submitting a tender base their price on the same set.
Thermal movement : Expansion or contraction caused by temperature
changes, which can lead to cracking in finishes.
Thread : A raised, helical ridge on a screw, nut, or bolt.
Timber ground : A length of timber, usually sawn, that contributes to the
fixing of another element.
Tongue and groove : The traditional detail for timber products used in
flooring and wall cladding, in which a projecting tongue on one long
face fits inside a compatible groove on the other. Planks and boards
interlock to ensure a level intersection. With composite boards, particularly
flooring products, a development of the basic form locks units together
and reduces the need for nail fixing.
Toughened glass : Glass with increased resistance to impact and tension
loading made by rapid heating and cooling during manufacture.
Translucent : Cannot be seen through but will allow light to pass through,
to varying degrees.
Transom : The horizontal framing member in a window or glazed screen.

Sole plate : The horizontal base member in a timber or metal stud

partition.
Specification : The written description, prepared by the designer, of the
quality of materials and construction required to complete a project to
an appropriate, acceptable standard. It may be contained on drawings,
in a separate document, or in a combination of both.

Transparent : Clear visibility through a material even if colour-tinted.

Tread : The horizontal element in a stair, which users step on.
Trimmed joist : A joist cut short to form a floor opening.
Trimmer joist : A joist that supports the ends of trimmed joist (see above).

Stairwell : The vertical space that contains a flight or flights of stairs.

It need not be fully enclosed unless used as a fire escape route.
Stanchion : A steel column, usually loadbearing.
Stretcher : A brick or block built into a wall so that its longer edge is
exposed.
String : The inclined structural support for the treads of a stair.
Studwork : The timber or metal framing that provides the support skeleton
for lightweight partition walls.
Subcontractor : An individual, or company, with specialist skills, usually
employed and supervised by the main contractor.

T
Tender : The price for which a contractor (see above) agrees to carry
out the work necessary to construct a project in accordance with the
tender drawings. It is normal for at least three contractors to be asked to
submit tenders, and for the contract to be awarded to the lowest bidder.
However, a designer must be satisfied that the work can be carried out
satisfactorily for the sum. When a single contractor is chosen for the job
usually because of particular expertise in a specialist area of work, or
previous successful collaboration with a client a negotiated contract is
entered into, in which contractor and designer collaborate to produce
a contract that will ensure the mutually acceptable completion of the
proposed work.

Trimming joist : A joist that supports the ends of trimmer joists (see above).
Turnbuckle : A device, integral to a tensioned structure, for carrying out
the final tightening of wires on site.

W
Well (or stairwell) : The volume that contains flight(s) of stair(s) and
landings.
Wired glass : Glass with a wire grid embedded in its core that provides
improved security and fire resistance.

188 A to Z

RESOURCES
FURTHER READING
1) Interior design focus:

4) Accepted standards for the configuration and

dimensions of elements:

Ashcroft, Roland, Construction for Interior Designers, 2nd

edition, Routledge, 1992

These will be crucial in assisting decision-making.

Moxon, Sian, Sustainability in Interior Design, Laurence

King Publishing, 2012
Yakeley, Diana, The BIID Interior Design Job Book, RIBA
Publishing, 2010

Baden-Powell, Charlotte, Architects Pocket Book, 3rd

edition, Architectural Press, 2008
Littlefield, David, Metric Handbook: Planning and Design
Data, 3rd edition, Architectural Press, 2008

5) Specialist techniques and materials:

2) Books aimed primarily at an architectural audience:
These contain information about interior construction
and are also a source of background information about
those exterior elements of buildings that may impact on
interior proposals.

These require specialist research those listed below are

examples of such sources.
Ballard Bell, Victoria and Patrick Rand, Materials for
Architectural Design, Laurence King Publishing, 2006

Ching, Francis D., Building Construction Illustrated, 4th

edition, Wiley, 2008

Binggeli, Corky, Materials for Interior Environments, Wiley,

2007

Chudley, Roy and Roger Greeno, Building Construction

Handbook, 8th edition, Butterworth Heinemann, 2010

Blanc, Alan and Sylvia, Stairs, Architectural Press, 2001

Emmitt, Stephen and Christopher Gorse, Barrys

Introduction to Construction of Buildings, 2nd edition,
Wiley, 2010
Emmitt, Stephen and Christopher Gorse, Barrys Advanced
Construction of Buildings, 2nd edition, Wiley, 2010
Hall, Fred and Roger Greeno, Building Services Handbook,
5th edition, Butterworth Heinemann, 2009
McLean, Will and Pete Silver, Introduction to Architectural
Technology, Laurence King Publishing, 2008

Booth, Sam and Drew Plunkett, Furniture For Interior

Design, Laurence King Publishing, 2014
Brown, Rachael, and Lorraine Farrelly, Materials and
Interior Design, Laurence King Publishing, 2012
Godsey, Lisa, Interior Design: Materials and Specifications,
Fairchild Publications, 2008
Innes, Malcolm, Lighting for Interior Design, Laurence King
Publishing, 2012
Kaltenbach, Frank (ed.), Translucent Materials: Glass,
Plastics, Metals, Birkhuser, 2004

3) Building legislation:
Decisions about construction and detailing are often
influenced by legislation.

Plunkett, Drew, Drawing for Interior Design, 2nd edition,

Laurence King Publishing, 2014

The Building Regulations 2000: Complete Set of Approved

Documents 2006, TSO (The Stationery Office), 2009

Reichel, Alexander, Anette Hochberg and Christine

Kopke, Plaster, Render, Paint and Coatings: Details, Products,
Case Studies, Birkhuser, 2004

Billington, M.J., K.T. Bright and J.R. Waters, Building

Regulations: Explained and Illustrated, 13th edition,
Blackwell, 2007

Rupp, William, Construction Materials for Interior Design:

Principles of Structure and Properties of Materials, Whitney

Resources 189

Library of Design, 1989

Spens, Michael, Staircases, Academy Editions, 1995
White Book, British Gypsum, 2009
A trade publication that is available in printed form and
for download at www.british-gypsum.com/literature/
white_book. It provides comprehensive information
about techniques and materials used in plasterboard
construction.
Wilhide, Elizabeth, Eco: The Essential Sourcework for
Environmentally Friendly Design and Decoration, 2nd
edition, Quadrille Publishing, 2004
Wilhide, Elizabeth, The Interior Design Directory: A
Sourcebook of Modern Materials, Quadrille Publishing, 2009

WEBSITES
Before the emergence of the Internet, interior designers
were obliged to maintain a reference library of catalogues
and brochures of products and materials, and to keep
this up to date, adding new items and removing obsolete
information. Manufacturers and suppliers now primarily
distribute information online, ensuring continuous
updating and, frequently, access to detailed drawings of
components that may be downloaded and incorporated
into designers own production drawings.

Timber Research and Development Association

www.trada.co.uk
Technical information about timber, timber-based
products and regulations; identification of species
and their structural capacities.
Networks and databases devoted to innovative new
materials and technologies.
www.materialconnexion.com
www.materio.com

2) Manufacturers and suppliers own websites:

These usually give comprehensive information about
individual manufacturers products, and increasingly
include advice about sustainability and details of
installation techniques. Examples are:
Expamet Building Products
www.expamet.co.uk
Manufacturer of expanded, metal materials, primarily
for plastering and rendering.
Hfele
www.hafele.co.uk
Manufacturer of furniture fittings and architectural
ironmongery.
National Building Specification
www.thenbs.com
Part of RIBA Enterprises Ltd, which produces specification
products for building construction, engineering services
and landscape design.

There are broadly two types of website:

1) Consortia of manufacturers and suppliers:

Below are examples of such sites.
British Glass
www.britglass.org.uk
Technical information and lists of specialist glass
manufacturers.
British Gypsum
www.british-gypsum.com
Information about plastering products and techniques
see also White Book, above.

Pilkington NSG Group Flat Glass Business

www.pilkington.com
Technology datasheets and information about standard
and specialist glass products.

190 A to Z

INDEX
Figures in italics refer to illustrations.
acid etching (of glass) 167
acrylic sheets 167
air conditioning 47, 49, 117
aluminium 165
for framing 22, 37, 37, 68, 165, 165
for skirtings 38
for stops and beads 165
arches, masonry 173
architraves 7, 76, 77, 79, 162
balustrades/banisters 100, 100, 145, 146, 150, 150, 151
battens see split battens
beams
circular 177, 177
concrete 15, 101
disguising 177, 177
laminated timber 100101, 161, 161, 173
loadbearing 15, 15, 172, 173, 173, 174, 174, 175, 175
oval 177, 177
sizing 181
steel 101, see also I section beams
supporting with padstones 98, 99
triangular 177, 177
bearing strength 19, 98
BIM (building information modelling) 10
biscuit jointing 132, 132, 162
blocks 173
concrete 20, 26, 99
glass 166167
sizes 26
block walls 26, 46, 54
bolts 169, 169
bonds 16, 17, 17, 26
bricks 16, 17, 26, 173
brick slips 17
brick walls 1617, 26, 54, 180, 180
chasing for pipes or wiring 49
cantilevered shelving 140, 140
cantilevered treads 152, 152, 153
cantilevers 176, 176
carpets 109, 161
cavity walls 17, 20, 2021, 21, 89
ceilings 114, 114
under concrete floors 114
curved 115, 116
fireproofing 121
and light fittings 114, 116, 117, 119
lowering 115, 117
plasterboard 114, 114
soundproofing 121
suspended 115, 115, 118, 118, 119, 120, 120
timber 114
see also cornices
ceiling slabs 172
chases/chasing 49, 110
chipboard 162
for flooring 102, 106, 106107, 107, 161
cladding see MDF; plasterboard; plywood
clout nails 30, 55, 168, 168
CLS (Canadian Lumber Sizes) stud framing 28, 54, 54, 160
CNC technology 10
columns 91, 172
concrete 101, 180
loadbearing capacity 98, 98, 175, 175
steel 101, 180
timber see posts
compression 172, 172, 173, 173
concrete 26, 173
concrete beams 101, 105
concrete blocks see blocks
concrete columns 101, 180
concrete floors 14, 88, 91, 106, 107
laying cables and pipes in 49, 88, 110
repairing 107
concrete walls 26, 46
and plumbing pipes 49

conduits 49, 49
cornices 6, 7, 42, 43
installing 42, 43
omitting 42, 43, 43
shadow gap 44, 44, 45
costs 910
countersinking screws 169
courses 16
cover strips 7, 62, 62, 63, 135
cross joints 128
curved walls 52, 5253, 53
block or brick 54
freestanding 56
glass 68, 69
stud partitions 54, 5455, 55
damp 2021, 89
damp proof courses 88, 89
damp proof membranes 20, 21, 21, 22, 22, 88, 89, 98
disabled access 102, 157
doors and door frames 8, 76
architraves 7, 76, 77, 79
and damp in walls 21, 22
double 85, 85
with fanlights 82, 82
and fire regulations 77, 85
folding sliding 81, 81
in glazed screens 83
hinges 76, 77
jambs and heads 76
lintels 18, 1819, 19, 23
non standard sized 84, 84
shadow gap frames 78, 78
sizes 76
sliding 80, 80
stops 7677, 78, 79, 79
unframed glass 83, 83
with vision panels 83, 83
with wired glass 83
double glazing 11, 166
dowel joints 129, 162
DPCs see damp proof courses
drawings, production/working 9, 10
dry lining walls 22, 22
dry rot 94, 160
drywall lining 27
aluminium framing 165, 165
finishing 3435
joints 32, 33
reinforcing corners 33, 33
drywall screws 30
ducting/ductwork 47, 117, 121, 121
electrical cables/wiring, installing
in ceilings 114, 115, 116
in floors and walls 47, 49, 49, 110, 111
English bond 17, 17
escalators 157
fanlights 82, 82
fin fixings 73, 73
finger joints 72, 72
fireproofing
of ceilings and floors 100, 111, 121
of metal columns and beams 48, 48
of walls 47
fire regulations
for doors 77, 85, 85
for stairs 157
Flemish bond 17, 17
floating floors 110, 111
floating furniture 139, 139
floating walls 58, 58, 59
base fixings for 60, 60
cladding 61, 61
floorboards 90, 90, 91, 91, 106, 107
composite 106, 106107, 107
veneered timber 108109
floors
altering 91
carpeting 109
chipboard 102, 106, 106107, 107, 161
concrete see concrete floors
fireproofing 111
installing new 100101
and loadbearing 91, 98

Index 191
making openings in 91, 104, 104105, 105
plastic and rubber tiled 108
plastic laminate 108, 109
raising 102, 102, 103
soundproofing 110, 111
stone and clay tiled 108
suspended 90
timber see floorboards
and ventilation 90
see also joists
floor slabs 172, 181
formwork 26
foundations, new 98, 98, 99, 99
framework, timber see stud partitions
furniture 124
aligning edges 135, 135
base structures 127, 127
floating 139, 139
legs 138, 138, 139, 139
pre fabricated aluminium 165
see also seating
glass
acid etching 167
brilliant cutting 167
clear float 166
curved 167
cutting and shaping 167
fire rated 166
laminated 166
opal 167
plate 166
sandblasting 167
sheet 166
toughened 166
wired 83, 166
glass blocks 166167
glass doors 83, 83
glass stairs 156, 156
glazed partitions 66, 6667, 67
curved 68, 69
framing and beading 68, 68, 69, 70, 70, 71
with hidden frames 71, 71
joining glass sheets for 72, 7273, 73
signs on 67
glazed screens 83, 166
gluing 168
goings (of stairs) 145
grout 108
handrails 145, 150, 150, 151, 155, 177
hangers, timber 115, 115, 116, 116
hardcore 88, 89
headers (bricks) 16, 17
head plates 27, 28
heating 38, 88
herringbone strutting 95, 95
hinges, door 76, 77, 83
I section beams, steel (RSJs) 91, 91, 96, 96, 97, 97, 105
cladding with plasterboard 48, 48, 101
depth and strength 175, 175
insulation 11, 20, 21, 22, 22
intumescent strips 85, 85
jambs 76, 77
joinery 124, 126
joints
biscuit 132, 132
mortar 16, 16
routed 131, 131
timber 101, 106, 107, 128, 128, 129, 130, 130, 132
joist hangers 92, 93, 104
joists, rolled-steel (RSJs) see I-section beams
joists, timber 92, 92
bracing with herringbone strutting 95, 95
ceiling 114, 114, 115, 115
cutting back when rotten 94, 94
depths and spans 91, 92, 95, 100
direction of 95
ground floor 90, 90
mezzanine 100
supporting 91, 91, 92, 92, 93, 93, 96, 96, 97, 98, 99
trimmer 93, 104, 105
upper floor 91, 91
laminated timber beams 100101, 161, 161, 173

landings 145, 155

lapped joints 129
lath and plaster 23, 114
lifts 102, 157
light fittings, ceiling 114, 116, 117, 119
linoleum flooring 108
lintels 18, 1819, 19, 20, 23, 173
loadbearing capacities 98, 164, 172175, 172175
see also walls, loadbearing
masonry see blocks; bricks
MDF (medium density fibreboard) 131, 160, 161, 162, 162
for cladding 61, 61
cutting 52
disadvantages of 162
finishing 162
for skirtings 38, 162
metal see aluminium; steel
metal lath sheeting 54, 55
metal split brackets 65, 65
mezzanines 100101, 177
mortar joints 16, 16, 17, 26
mortice and tenon joints 130, 132
nails 168, 168
clout 30, 55, 168, 168
noggings 28, 29, 54, 54, 55
nosing (of stair treads) 145, 146, 147, 147
nuts and bolts 169, 169
opal glass 167
OSB (oriented strand board) 95, 102, 160, 161, 162
outriggers 59
padstones 98, 99
panel pins 168
PAR timber 160, 160, 161
particle boards 95
partitions
base fixings for 60, 60
cladding for floating 61, 61
demountable 6465
fixing decorative panels to 62
shadow gap 62, 62, 63
see also glazed partitions; stud partitions
party walls 17, 99
Perspex 167
piers 15, 15, 180
pipes, installing
behind partition walls 49, 49
behind skirtings 38
in floors 49, 88, 110, 111
surface mounted in conduits 49, 49
in suspended ceilings 115
plaster and plastering 17, 22, 26
and aluminium stops and beads 23, 165
of curved walls 54, 55
removing from brickwork 17
skimming plasterboard 26, 27, 32, 32
plasterboard 26, 27, 164, 164
bending 5455, 55
butting to existing wall 23, 23
ceilings 114, 114
for cladding 48, 48, 61, 61, 101
cutting 52, 164
for dry lining walls 22, 22
fixing 28, 28, 30, 31, 168, 168
joints 32, 32
loadbearing capacity 164
protecting corners and edges of 32, 164
sizes 11, 27
skimming 26, 27, 32, 32
see also drywall lining
plastering see plaster and plastering
plastic cladding 17, 61, 61
plastic laminate flooring 108, 109
Plexiglas 167
plugs, timber 130, 130
plumbing see pipes, installing
plywood 52, 134, 161, 162, 163
cladding with 61, 61, 179
veneers 163, 163
point loads 98
pointing 16
posts, timber 60, 60, 101, 181
pugging 110, 121

192 A to Z
PVB (polyvinyl butyral) laminating 166
ramps 102, 157
risers (of stairs) 145, 145
rot, wet and dry 90, 92, 92, 94, 94, 160
routing techniques 131, 131
RSJs (rolled steel joists) see I section beams
sandblasting glass 167
saws, machine 125
screeds/screed surfaces 88, 106
screws 30, 169
hiding heads 130
scrim tape 32, 32, 33, 33, 34, 43, 43
sealing round frames 21, 21
seating
built in 136, 136137, 137
tiered 103
shadow gaps 7
and angled and curved walls 53
cornices 44, 44, 45
door frames 78, 78
and furniture 135
partitions 62, 62, 63
skirtings 7, 40, 40, 41, 41
shelves/shelving 35
cantilevered 140, 140
for heavier loads 141, 141
suspended 140, 140
shuttering 26
sizing, standard 11, 11
skirtings 6, 7, 38, 39, 76, 78
and gaps 38
incorporating heating 38
MDF 38, 162
and new floors 109, 109
shadow gap 40, 40, 41, 41
sliding doors 80, 80, 81, 81
sole plates 28
soundproofing
of ceilings 121
of floors 110, 111
and sliding doors 80
of walls 46, 4647
split battens, timber 6465, 65, 141, 141
split brackets, metal 65, 65
stainless steel 165
stairs 144
angled 144, 144
with cantilevered treads 152, 152, 153
concrete 147, 147, 152, 152
cutting openings for 91, 104, 104105, 105
dog leg 144, 144, 147
and fire regulations 157
folded plate 149, 149
glass and steel 156, 156
and headroom 105, 144
to mezzanines 100, 100
open tread 145, 14647
spiral 144, 144145, 154, 154, 155
steel 148, 148149, 149, 152, 152
stone 147
straight flight 144, 144
timber 146, 14647, 147
see also handrails
stairwells 145
stanchions 101
steel 19, 165, 173
see also I section beams; stairs
steps, framing 103
stop moulding 23, 23
stops, door 7677, 78, 79, 79
stretcher bonds 17, 17, 26
stretchers (bricks) 16, 17
strings (of stairs) 145, 145, 146, 147
stud partitions 23, 26, 27, 27, 28, 2829, 30, 3031
cladding with invisible fixings 64, 6465, 65
corners and junctions 36, 36, 37
curved 54, 5455, 55
fixing skirtings to 39
freestanding 56
metal framing for 37, 37
soundproofing 46, 46, 47
and stability 178
see also drywall lining; plasterboard

tenders 9
tension 172, 172
tension wires and rods 179
tiles, floor 108
timber 160, 173
composite 161
hardwood 160
PAR 160, 160
sawn 160, 160
softwood 160
see also beams
timber ceilings 114
timber columns see posts
timber connectors 101, 101
timber split battens 6465, 65
tongue and groove joints 106, 107, 132
treads, stair 145, see stairs
veneers 133, 133
edging 134, 134
for flooring 108109
plywood 163, 163
ventilation (under floors) 90
vision panels (in doors) 83, 83
wall plates 92, 92, 94, 94, 153
walls 172
cavity 17, 2021, 89
concrete 26, 46, 49
damp proofing 20, 21, 21, 22, 22, 88, 89
dry lining 22, 22
dwarf 90, 90
floating 58, 58, 59
freestanding 56, 56, 57, 57, 180
lath and plaster 23, 114
lining external 22, 22
loadbearing 14, 14, 15, 15, 16, 17, 95, 98, 98
non loadbearing 14, 23, 26, 95
party 17, 99
see also stud partitions
wall ties 20
washers 169, 169
weep holes 89
wet rot see rot, wet and dry
windows 20, 21, 21
framing and beading 70, 70, 71
and multiple glazing 166
wiring see electrical cables/wiring
workshops 124, 126, 126

Picture credits
All diagrams are by Olga Valentinova Reid and all
photographs are by Drew Plunkett, except the following:
vp.156 top
Katsuhisa Kida / FOTOTECA
p.156 bottom Peter Paige Photography
Alexander Franklin Photography.
p.165 left

Designers: Brinkworth Design

Acknowledgements
Thanks to:
Olga Valentinova Reid for converting my crude sketches
into elegant drawings and diagrams and then designing
the book.
Alan Keane for demonstrating and explaining workshop
practice.