BBE 510 – CONSTRUCTION TECHNOLOGY

MATERIALS AND THE CONSTRUCTION OF

BUILDING ELEMENTS
INTRODUCTION

A building is an assemblage that is firmly attached to the ground and that provides total or
nearly total shelter for machines, processing equipment, performance of human activities,
storage of human possessions, or any combination of these.
When designing a building, an architect plans for spatial, environmental and visual
requirements. Once these requirements are satisfied, it is necessary to detail the fabric of the
building. The choice of materials and the manner in which they are put together to form
building elements, such as the foundation, walls, floor and roof, depend largely upon their
properties relative to environmental requirements and their strength.
Building construction is generally performed by laborers and craftspeople engaged for the
purpose by an individual or organization, called a contractor. The contractor signs an
agreement, or contract, with the building owner under which the contractor agrees to construct
a specific building on a specified site and the owner agrees to pay for the materials and services
provided.
The process of building construction thus involves an understanding of: the nature and
characteristics of a number of materials; the methods to process them and form them into
building units and components; structural principles; stability and behavior under load;
building production operations; and building economics.

BUILDING SYSTEMS
A system is a collection of elements or subcomponents, that are interrelated to form a unified
whole. The building systems is made up of several components.

Vertical section through a one-story building with basement shows location of some major
components. (F. S. Merritt and J. Ambrose, ‘Building Engineering and Systems Design,’’ 2d
ed., Van Nostrand Reinhold, New York.)
 Substructure system - can be defined as all structure below the superstructure which in
general terms is considered to include all structure below ground level but including
the ground floor bed.

 Superstructure system - The portion of a building that extends above the ground level
outside
 Internal Finishes - The interior of a building usually is compartmented into spaces or
rooms by horizontal dividers (floor-ceiling or roof-ceiling systems) and vertical
dividers (interior walls and partitions). (The term partitions is generally applied to non-
load-bearing walls.)
 External Envelope - consists of the materials and components which form the external
shell or enclosure of a building. These may be load bearing or non-load bearing
according to the structural form of the building.
 Services (Electrical system, Plumbing Systems, Mechanical Systems)
CONSTRUCTION MATERIALS
There are many types of building materials used in construction such as Concrete, Steel, Wood
and Masonry. Each material has different properties such as weight, strength, durability and
cost which makes it suitable for certain types of applications. The choice of materials for
construction is based on cost and effectiveness to resisting the loads and stresses acting on the
structure.
The manufacturing of building materials is a well-established and standardized industry
capable of providing a reliable supply of high-quality materials for our structures. The
production of structural-grade building materials is subject to quality control procedures that
involve inspection and testing according to national standards and scientific testing methods.
Building materials can generally be divided into two categories:
 Natural building materials such as stone and wood, and
 Man-made building materials such as concrete and steel.
Both categories usually require a certain level of preparation or treatment before the use in a
structural application.
Types of Building Materials
A. Concrete:
Concrete is a composite material made from mixing cement, aggregates such as sand and
crushed stone and water. The properties of concrete depend on the ratios used in the mix design.
Therefore, it’s a standard practice for concrete suppliers to provide material properties and test
results for each concrete batch.
Fresh concrete can be poured into formworks to take any shape or form and takes time to harden
into a stone-like material. It takes up to 7 days for concrete to reach the majority of its strength
and will need special attention to curing to avoid cracking or reduction in capacity.
The concrete will become hard in a matter of hours, but takes about 28 days to reach its full
strength. Therefore, it is usually propped up until that period. During this time the concrete
must be cured, or supplied with water on its surface, which it needs for the chemical reactions
within to proceed properly.
Concrete is very versatile and a go to material for applications that require a combination of
strength and durability. For example, concrete is an excellent material for building
foundations where the weight of the structure meets the ground. This requires strength to carry
the load and also durability to withstand the contact with the surrounding soil.
Concrete is very strong when exposed to compression stresses. However, it’s brittle and has
limited tensile strength. Combined with steel rebar, reinforced concrete is stronger and more
suitable for a wide range of structures such as tall multi-story buildings, bridges, roads, tunnels
and so many other applications.
Concrete that is cast in place in its mould is called cast-in-situ concrete. Concrete members that
are cast in a concrete factory and then shipped to site are called precast concrete.
TYPES OF CONCRETE
The most common types of concrete are:
 High Strength Concrete: the most basic and important property of concrete is its
compressive strength. Concrete with a compressive strength of 40Mpa (5,800 psi) is
called high strength concrete.
 High Performance Concrete: is a new term for some concretes being developed today.
It is a fairly broad term that describes concretes that outperform "normal", everyday
concrete in one or more characteristics such as lifespan, lifespan in corrosive
environments, permeability, density, ease of placement, or many other parameters.
 Lightweight Concrete: is made by using small, lightweight aggregates, such as small
balls of styrofoam (thermocole) or by adding foaming agents to the mix of concrete.
Lightweight concretes have low structural strength, and are used mostly in non-
structural elements. The best is example is aerated autoclaved concrete (AAC) blocks
used for making walls. Also called cellular concrete or aerated concrete.
 Self-Consolidating Concrete, also called Self Compacting Concrete:
 Sprayed Concrete or Shotcrete: you can actually spray concrete onto a surface to
form a thick, uneven coating. This process is different from other concreting methods
in that the concrete is not poured into a form or mould. It is sprayed directly onto a
surface, and is used in infrastructure projects and to repair old, cracked concrete
surfaces. Shotcreting is also called guniting.
 Water-resistant Concrete: normal concretes are permeable to water; that is, they allow
water to pass through. Water resistant concretes are engineered to have fine particle
cement replacements that do not allow water to pass through. These are very useful for
construction below ground, like basements, as well as water retaining structures like
water tanks and dams, and of course marine structures like jetties and bridges.
 Micro reinforced concretes: are a new generation of high-tech concretes. They contain
small steel, fibreglass or plastic fibres that dramatically alter the properties of concrete.

B. Steel:
Steel is one of the strongest building materials available with excellent strength capacity in
both tension and compression. Because of its high strength-to-weight ratio, it is ideal for
structural framework of tall buildings and large industrial facilities. Structural steel is available
in standard shapes such are angles, I beams and C-channels. These shapes can be welded
together or connected using high-strength bolts to build structures capable of resisting large
forces and deformations.
The other important feature of steel framing is its flexibility. It can bend without cracking,
which is another great advantage, as a steel building can flex when it is pushed to one side by
say, wind, or an earthquake. The third characteristic of steel is its plasticity or ductility. This
means that when subjected to great force, it will not suddenly crack like glass, but slowly bend
out of shape.
This property allows steel buildings to bend out of shape, or deform, thus giving warning to
inhabitants to escape. Failure in steel frames is not sudden - a steel structure rarely collapses.
Steel in most cases performs far better in earthquake than most other materials because of these
properties.
However, one important property of steel is that it quickly loses its strength in a fire. At 500
degrees celsius (930 degrees F), mild steel can lose almost half its strength. This is what
happened at the collapse of the World Trade Towers in 2001. Therefore, steel in buildings must
be protected from fire or high temperature; this is usually done by wrapping it with boards or
spray-on material called fire protection.
Steel is a relatively expensive building material so it is the structural engineer’s responsibility
to choose economic sizes and shapes according to the actual loads on the building to avoid
overdesign. The installation of steel is less time consuming compared to concrete and can be
installed in any type of environment.
Wood:
Wood has been used as a construction material for thousands of years and if properly
maintained can last for hundreds of years. It is a readily available and economically feasible
natural resource with a light weight and highly machinable properties. It also provides good
insulation from the cold which makes it an excellent building material for homes and residential
buildings.
Wood pieces used in construction are machine-planed and sawn into certain dimensional
specifications. Dimensional lumber comes in widely available sections such as 2”x4”, 2”x6”,
etc. This is commonly used in the construction of walls and floors. Believe it or not, a 2”x4” is
actually 1 ½” wide x 3 ½” high. Wood that comes in larger dimensions are referred to as timber
or beams and are commonly used to construct the frames of large structures such as bridges
and multi-story buildings. Engineered wood is another type of wood used in construction that
consist of various forms of wood glued together to form a composite material suitable for
specific construction applications. Examples of engineered wood is glued laminated wood
(glulam), plywood and fiberboard.
Because of its light weight, wood is not the most suitable construction material to
support heavier loads and not ideal for long spans. Wood is rarely used for foundations and
basement walls, as it needs to be pressure treated because of its contact with soil/moisture
which can be fairly expensive. In a wood framed house, the foundations and basement walls
are usually constructed with reinforced concrete.
TYPES OF WOOD
Wood has traditionally been classified into two primary categories:
 Hardwood (any leaf-bearing tree) and
 softwood (any cone-bearing tree).
As with most other general classifications, this can get somewhat confusing due to the fact that
there are some leaf-bearing trees that can have relatively soft wood, while some coniferous
trees that can have rather hard wood. Generally speaking, however, hardwoods are by and large
considered to be heavier and denser than softwoods. Hardwoods are commonly used in the
construction of walls, ceilings and floors, while softwoods are often used to make doors,
furniture and window frames. Some examples of the most popular hardwoods include oak,
maple, mahogany, cherry, walnut, and teak. Commonly used softwoods include pine, hickory,
beach, ash, birch, and cedar.
LUMBER GRADES
The National Hardwood Lumber Association (NHLA) of America has created a grading system
to rate various types of lumber, primarily based on the amount of defects that can be found in
a board. Below is a brief summary of NHLA grades for both hardwood and softwood lumber.
Hardwoods
1. First and Seconds (FAS) - This is the highest grade possible for hardwood lumber, and is
mainly suited for high-quality furnishings, solid wood mouldings and interior joinery. Contains
83% usable material on one face (minimum 6" x 8" board size).
2. Select (Sel) - Also contains 83% usable material, but for a smaller minimum board size (4"
x 6") than FAS.
3. #1 Common (#1 Com) - Contains 66% usable material on a 3" x 4" board face.
4. #2 Common (#2 Com) - Contains 50% usable material on a 3" x 4" board face.

Softwoods
1. C Select - Almost completely free of all defects; commonly used for cabinets and interior
trim
2. D Select - Comparable to C Select, but may contain small knots (no bigger than the size of
a dime)
3. 1 Common - Contains small, tight knots that won't fall out; offers a high-quality knotty
appearance (e.g., pine)
4. 2 Common - Very similar to 1 Common, but with slightly larger knots; often used in shelving
and paneling
5. 3 Common - Larger knots that what are found in 2 Common; typically used for crates, boxes
and fences
BENEFITS OF WOOD IN CONSTRUCTION
Wood carries several benefits that make it an excellent candidate for use in a wide array of
construction projects. One such benefit is its thermal properties, which give it an advantage in
terms of its resistance to high temperatures. Unlike steel, which can expand or even collapse in
high heat, wood actually dries out and becomes stronger as the heat increases. In addition, the
heat conductivity of wood is relatively low in comparison to other materials such as aluminum,
marble, steel, or glass. This gives wood an advantage in terms of being used in various
applications such as matches, hardware equipment handles, wall coverings, and ceilings.
Wood also contains highly-sought-after acoustic properties. It can absorb sound and echoes,
and is a favorite material of choice for the construction of structures where proper acoustics is
important, such as concert halls. Wood is resistant to electrical currents, making it an optimal
material for electrical insulation. Another important characteristic of wood is its tensile
strength, which is its ability to bend under pressure without breaking. Wood is exceptionally
light in proportion to its tensile strength, making it the preferred construction choice for
surfaces that take a constant beating such as basketball courts and bowling lanes. Tensile
strength is also one of the main reasons for choosing timber as a building material; its
remarkably strong qualities make it the perfect choice for heavy-duty building materials such
as structural beams.
Of the many construction materials that a person can choose from, wood stands out as a unique
and amazingly versatile product. Its aesthetic appeal, tensile strength, insulation qualities, and
ease of fabrication enable it to remain a favorite choice for use in an extensive array of
construction applications.
C. Masonry:
Masonry construction is using individual units to build structures that are usually uses mortar
to bound the units together. The most common material I use in the design of masonry
structures is concrete block, with vertical steel reinforcing if required. Masonry is strong in
resisting compression loads/stresses which makes it ideal to use for the construction of load
bearing walls. Other masonry materials include brick, stone and glass block. Masonry is a
highly durable and fire resistant material, however it can be sensitive to mortar and
workmanship quality.
There has been an increase in the use of masonry as load bearing walls for the design of multi-
story buildings in my office. The structural system typically consists of concrete floors
supported on a combination of masonry and reinforced concrete walls depending on the number
of floors and amount of load on the walls. Masonry walls with windows or openings need
horizontal beams or lintels to span the weight of the wall above across the opening. Masonry
is not as accommodating to large openings in walls as concrete or steel framing is, but can be
an economical choice if the framing and opening sizes are reasonable and length of wall
segments are not too short.
Load bearing masonry walls can be stacked up on top of one another to build multi-story
buildings. The load on the first floor masonry wall is the accumulation of all the weight of the
floors above it. Therefore, the bottom floor wall must be stronger than the upper floor walls.
This can be achieved by reinforcing the voids in the bottom masonry walls with steel bars and
concrete grout. More steel bars closer spacing of grouted cores equals stronger masonry walls.
If a load bearing masonry wall does not extend all the way down to the foundation because of
required openings such as parkade drive aisles, large concrete or steel transfer beams are
required to support the wall above the opening.
D. GLASS
Glass has been a fascinating material to humankind since it was first made in about 500 BC.
At first thought to possess magical properties, glass has come a long way. It is one of the most
versatile and oldest materials in the building industry. From its humble beginnings as a
window pane in luxury houses of Pompeii to sophisticated structural members in new age
buildings, its role in architecture has evolved over the years.
HOW GLASS IS USED IN CONSTRUCTION

From the beginning of 20th century modern architecture has been instrumental in mass
production of concrete, glass and steel buildings in the factories we call cities. This ideology
helped accommodate housing needs of the burgeoning middle class. Glass and steel
construction have become the symbol of development in many countries, where people tend to
see these buildings as symbols of affluence and luxury.
PROPERTIES OF GLASS
 Transparency: This property allows visual connection with the outside world. Its
transparency can be permanently altered by adding admixtures to the initial batch mix.
By the advent of technology clear glass panels used in buildings can be made opaque.
(Electro chromatic glazing).
 U value: The U-value is the measure of how much heat is transferred through the
window. The lower the U-value the better the insulation properties of the glass– the
better it is at keeping the heat or cold out.
 Strength: Glass is a brittle material but with the advent of science and technology,
certain laminates and admixtures can increase its modulus of rupture (ability to resist
deformation under load).
 Greenhouse effect: The greenhouse effect refers to circumstances where the short
wavelengths of visible light from the sun pass through glass and are absorbed, but the
longer infrared re-radiation from the heated objects are unable to pass through the glass.
This trapping leads to more heating and a higher resultant temperature.
  Workability: It is capable of being worked in many ways. It can be blown, drawn or
pressed. It is possible to obtain glass with diversified properties- clear, colorless,
diffused and stained. Glass can also bewelded by fusion.
 Recyclable: Glass is 100% recyclable, cullets (Scraps of broken or waste glass gathered
for re-melting) are used as raw materials in glass manufacture, as aggregates in concrete
construction etc.
 Solar heat gain coefficient: It is the fraction of incident solar radiation that actually
enters a building through the entire window assembly as heat gain.
 Visible transmittance: Visible transmittance is the fraction of visible light that comes
through the glass.
 Energy efficiency and acoustic control: Energy-efficient glazing is the term used to
describe the double glazing or triple glazing use in modern windows in homes. Unlike
the original single glazing or old double glazing, energy-efficient glazing incorporates
coated (low-emissivity) glass to prevent heat escaping through the windows. The air
barrier also enhances acoustic control.
TYPES OF GLASS
 Float Glass: Float glass is also called soda lime glass or clear glass. This is produced
by annealing the molten glass and is clear and flat. Its modulus of rupture is 5000-6000
psi. Stronger than Rocky Balboa taking punches from 2000 psi punches man Ivan
Drago. It is available in standard thickness ranging from 2mm to 20mm. and has weight
range in 6-26kg/m2. It has too much transparency and can cause glare. It is used in
making canopies, shop fronts, glass blocks, railing partitions, etc.
 Tinted Glass: Certain additions to the glass batch mix can add color to the clear glass
without compromising its strength. Iron oxide is added to give glass a green tint; sulphar
in different concentrations can make the glass yellow, red or black. Copper sulphate
can turn it blue. Etc.
 Toughened Glass This type of glass is tempered, may have distortions and low visibility
but it breaks into small dice-like pieces at modulus of rupture of 3600 psi. Hence it is
used in making fire resistant doors etc. They are available in same weight and thickness
range as float glass.
 Laminated Glass: This type of glass is made by sandwiching glass panels within a
protective layer. It is heavier than normal glass and may cause optical distortions as
well. It is tough and protects from UV radiation (99%) and insulates sound by 50%.
Used in glass facades, aquariums, bridges, staircases, floor slabs, etc.
 Shatterproof glass: By adding a polyvinyl butyral layer, shatter proof glass is made.
This type of glass does not from sharp edged pieces even when broken. Used in
skylight, window, flooring, etc
 Extra clean glass: This type of glass is hydrophilic i.e. The water moves over them
without leaving any marks and photocatylitic i.e. they are covered with Nanoparticles
that attack and break dirt making it easier to clean and maintain.
 Double Glazed Units: These are made by providing air gap between two glass panes in
order to reduce the heat loss and gain. Normal glass can cause immense amount of heat
 gain and upto 30%of loss of heat of air conditioning energy. Green, energy efficient
glass can reduce this impact.
 Chromatic glass: This type of glass can control daylight and transparency effectively.
These glass are available in three forms- photochromatic (light sensitive lamination on
glass), thermochromatic (heat sensitive lamination on glass) and electrochromatic (light
sensitive glass the transparency of which can be controlled by electricity switch.) It can
be used in meeting rooms and ICUs
 Glass wool: Glass wool is a thermal insulation that consists of intertwined and flexible
glass fibers, which causes it to "package" air, and consequently make good insulating
materials. Glass wool can be used as filler or insulators in buildings, also for
soundproofing.
 Glass blocks: Hollow glass wall blocks are manufactured as two separate halves and,
while the glass is still molten, the two pieces are pressed together and annealed. The
resulting glass blocks will have a partial vacuum at the hollow center. Glass bricks
provide visual obscuration while admitting light
PROPERTIES OF GLASS
 Polycarbonate: This elastic is 300 times stronger than glass, is resistant to most
chemicals, is twice as lighter than class, has high abrasion and impact resistance. It can
transmit as much light as glass without many distortions. Applications include window,
green house glazing etc.
 Acrylic: Acrylic is made of thermo plasticsis weather resistant, is 5 times stronger than
glass but is prone to scratches. It has excellent optics, is softer than glass but can
accumulate a lot of dust. This is extensively used in to make playhouses, green house
etc.
 GRP panels: GRP is manufactured by combining hundreds of glass strands together
using a pigmented thermosetting UV resin.Glass-reinforced plastics are also used to
produce house building components such as roofing laminate, canopies etc. The
material is light and easy to handle. It is used in the construction of composite housing
and insulation to reduce heat loss.
 ETFE: Ethylene tetrafluoroethylene is a plastic with high strength and corrosion
resistance. It has high energy radiation resistance properties, it is strong, self cleaning
and recyclable.
The versatility of glass keeps on increasing as scientists find new applications to this wonder
material. Glass is now being used in the building industry as insulation material, structural
component, external glazing material, cladding material; it is used to make delicate looking
fenestrations on facades as well as conventional windows. With the advent of green technology
in construction, glass is constantly undergoing transformation. Solar power glass, switchable
glass projection screens are a few of the newer uses. This is one material to look out for!
E. PLYWOOD
Plywood as a building material is very widely used due to its many useful properties. It is an
economical, factory-produced sheet of wood with precise dimensions that does not warp or
crack with changes in atmospheric moisture.
Ply is an engineered wood product made from three or more 'plies' or thin sheets of wood.
These are glued together to form a thicker, flat sheet. The logs used to make plywood as a
building material are prepared by steaming or dipping in hot water. They are then fed into a
lathe machine, which peels the log into thin plies of wood. each ply is usually between 1 and
4mm thick.
USES OF PLYWOOD AS A BUILDING MATERIAL
Plywood has a huge range of used within the construction industry. Some of its most common
uses are:
 To make light partition or external walls
 To make formwork, or a mould for wet concrete
 To make furniture, especially cupboards, kitchen cabinets, and office tables
 As part of flooring systems
 For packaging
 To make light doors and shutters
HOW PLY IS MADE
Plywood consists of the face, core, and back. The face is the surface that is visible after
installation, while the core lies between the face and back. Thin layers of wood veneers are
glued together with a strong adhesive. This is mainly a phenol or urea formaldehyde resin.
Each layer is oriented with its grain perpendicular to the adjacent layer. Plywood as a building
material is generally formed into large sheets. It may also be curved for use in ceilings, aircraft,
or ship building.
WHICH WOOD IS PLY MADE OF?
Plywood is manufactured from softwood, hardwood, or both. The hardwoods used are ash,
maple, oak, and mahogany.Douglas fir is the most popular softwood for making plywood,
although pine, redwood, and cedar are common. Composite plywood can also be engineered
with a core of solid timber pieces or particleboard, with a wood veneer for the face and back.
Composite plywood is preferable when thick sheets are required.
Additional materials can be added to the face and back veneers to improve durability. These
include plastic, resin-impregnated paper, fabric, Formica, or even metal. These are added as a
thin outer layer to resist moisture, abrasion and corrosion. They also facilitate better binding of
paint and dyes.
PROPERTIES
1. High Strength: Plywood has the structural strength of the wood it is made from. This
is in addition to the properties obtained from its laminated design. The grains of each
veneer are laid at 90 degree angles to each other. This makes the whole sheet resistant
to splitting, especially when nailed at the edges. It also gives the whole sheet uniform
strength for increased stability. Furthermore, plywood has a higher strength to weight
ratio as compared to cut lumber. This makes it ideal for flooring, webbed beams, and
shear walls.
2. High panel shear: Plywood is made with an odd number of layers, making it tough to
bend. The angle at which the veneer grains are laid against each other may be varied
 from 90 degrees. Each veneer can be laid at a 45 or 30 degree angle to the next one,
increasing the plywood’s strength in every direction. This cross lamination increases
the panel shear of plywood, important in bracing panels and fabricated beams.
3. Flexibility: Unlike cut timber, plywood can be manufactured to fit every requirement.
The thickness of each veneer can vary from a few millimeters to several inches. The
number of veneers used also ranges from three to several, increasing the thickness of
the sheet. The extra layers add more strength to the plywood. Thinner veneers are used
to increase flexibility for use in ceilings and paneling.
4. Moisture resistance: The type of adhesive used to bind the veneers makes the plywood
resistant to moisture and humidity. A layer of paint or varnish can also increase
resistance to water damage. These types of veneers are suitable for exterior use such as
cladding, sheds, and in marine construction. They are also suited for holding concrete
while it sets. Moisture resistance is important in interior applications as well, including
on floors. The cross lamination ensures the veneers do not warp, shrink, or expand when
exposed to water and extreme temperature.
5. Chemical resistance: Plywood treated with preservative does not corrode when
exposed to chemicals. This makes it suitable for chemical works and cooling towers.
6. Impact resistance: Plywood has high tensile strength, derived from the cross
lamination of panels. This distributes force over a larger area, reducing tensile stress.
Plywood is therefore able to withstand overloading by up to twice its designated load.
This is critical during short-term seismic activity or high winds. It is also useful in
flooring and concrete formwork.
7. Fire resistance: Plywood can be treated with a fire resistant chemical coating. More
commonly, it is combined with non-combustible materials such as plasterboard or
fibrous cement. This makes it ideal for use in fire resistant structures.
8. Insulation: Plywood has high thermal and sound insulation. This makes it a useful
insulating material for flooring, ceilings, roofing, and wall cladding. Insulation offered
by plywood can greatly reduce heating and cooling costs.
TYPES OF PLYWOOD
 Structural plywood: Used in permanent structures where high strength is needed. This
includes flooring, beams, formwork, and bracing panels. It can be made from softwood
or hardwood.
 External plywood: Used on exterior surfaces where a decorative or aesthetic finish is
important. It is not used to bear loads or stress, such as on exterior door surfaces, and
wall cladding.
 Internal plywood: This has a beautiful finish, for non-structural applications like wall
paneling, ceilings, and furniture.
 Marine plywood: It is specially treated using preservatives, paint, or varnish, to resist
water damage. It is used in shipbuilding, resists fungal attacks and does not delaminate.
GRADES OF PLYWOOD
Plywood grades are determined by strength, discolorations, surface defects, and resistance to
moisture, among other properties. The quality of surface veneer, type of wood, and strength of
adhesive, will then be allocated a particular rating. Each rating will determine the type of
application the plywood is suited for.
Plywood grades are N, A, B. C, and D. The D grade has several surface defects such as graining
and knotting, while the N grade has few of these. An “interior C-D” rating for example,
indicates the plywood has a grade C face, and a grade D back. It also means the adhesive is
suited for interior applications.
The unique characteristics of plywood, its cost effectiveness, and ease of use will continue to
popularize plywood as a building material.
ASPHALT AND BITUMINOUS PRODUCTS
Asphalt, because of its water-resistant qualities and good durability, is used for many building
applications to exclude water, provide a cushion against vibration and expansion, and serve as
pavement.
ASPHALTS FOR DAMP PROOFING AND WATERPROOFING: Damp proofing is
generally only a mopped-on coating, whereas waterproofing usually is a built-up coating of
one or more plies. Bituminous systems used for damp proofing and waterproofing may be hot
applied or cold applied.
JOINT SEALS
Calking compounds, sealants, and gaskets are employed to seal the points of contact between
similar and dissimilar building materials that cannot otherwise be made completely tight. Such
points include glazing, the joints between windows and walls, the many joints occurring in the
increasing use of panelized construction, the copings of parapets, and similar spots.
PAINTS AND OTHER COATINGS
 Protective and decorative coatings generally employed in building are the following:
 Oil Paint. Drying-oil vehicles or binders plus opaque and extender pigments.
 Water Paint. Pigments plus vehicles based on water, casein, protein, oil emulsions, and
rubber or resin atexes, separately or in combination.
 Calcimine. Water and glue, with or without casein, plus powdered calcium carbonate
and any desired colored pigments.
 Varnish. Transparent combination of drying oil and natural or synthetic resins.
 Enamel. Varnish vehicle plus pigments.
 Lacquer. Synthetic-resin film former, usually nitrocellulose, plus plasticizers, volatile
solvents, and other resins.
 Shellac. Exudations of the lac insect, dissolved in alcohol.
 Japan. Solutions of metallic salts in drying oils, or varnishes containing asphalt and
opaque pigments.
 Aluminum Paint. Fine metallic aluminum flakes suspended in drying oil plus resin, or
in nitrocellulose.
BASIC COMPONENTS OF A BUILDING STRUCTURE
SUBSTRUCTURE
The basic components of a building structure are the foundation, floors, walls, beams, columns,
roof, stair, etc. These elements serve the purpose of supporting, enclosing and protecting the
building structure.
Mentioned below are the 12 basic components a building structure.
 Roof
 Parapet
 Lintels
 Beams
 Columns
 Damp proof course (DPC)
 Walls
 Floor
 Stairs
 Plinth Beam
 Foundation
 Plinth
These are then categorized into two major components of a building namely substructure and
superstructure. The substructure is the part of the building that is built below the ground level
whereas superstructure is the part of the structure that is constructed above the ground level.
The substructure is the lower part of a building which is constructed below the ground level.
The function of substructure is the transfer of loads from the superstructure to the underlying
soil. So, the substructure is in direct contact with supporting soil. Substructure involves footing
and plinth of a building.
An experienced structural engineer should generate plans and works for the substructure of a
building project. Added to that, structural engineers are responsible for computing stresses and
loads which are required to be supported by the building under consideration. Lastly, structural
engineers need to comprehend how to incorporate support beams, columns and foundations
into the substructure plans.
Differences between superstructure and substructure of a building

Superstructure Substructure

Part of a building that constructed above ground Portion of a building that constructed
level below ground level

It transfers loads received from

It serves the purpose of building’s intended use
superstructure to supporting soil

Superstructure elements include walls, columns, Elements of substructure include

beams, doors and windows, etc. foundation and plinth.
SUBSTRUCTURE
The substructure is the lower part of a building which is constructed below the ground level.
The function of substructure is the transfer of loads from the superstructure to the underlying
soil. So, the substructure is in direct contact with supporting soil. Substructure involves footing
and plinth of a building.
The footing and foundation should be made of a material that will not fail in the presence of
ground or surface water. Before the footing for the foundation can be designed, it is necessary
to determine the total load to be supported. If, for some reason, the load is concentrated in one
or more areas, this will need to be taken into consideration. Once the load is determined, the
soil-bearing characteristics of the site must be studied.
The footing should never be placed on a filled area unless there has been sufficient time for
consolidation. This usually takes at least one year with a normal amount of rainfall. The bearing
capacity of soil is related to the soil type and the expected moisture level.
If a building site with poor natural drainage must be used, it can be improved by the use of
contour interceptor drains or subsurface drains in order to cut off the flow of surface water or
to lower the level of the water table. Apart from protecting the building against damage from
moisture, drainage will also improve the stability of the ground and lower the humidity of the
site.
An experienced structural engineer should generate plans and works for the substructure of a
building project. Added to that, structural engineers are responsible for computing stresses and
loads which are required to be supported by the building under consideration. Lastly, structural
engineers need to comprehend how to incorporate support beams, columns and foundations
into the substructure plans.
Foundation
The Foundation is a structural unit that uniformly distributes the load from the superstructure
to the underlying soil. This is the first structural unit to be constructed for any building
construction. A good foundation prevents settlement of the building.
Types of foundation
Foundations may be divided into several categories suitable for specific situations.
1. Continuous wall foundations may be used either as basement walls or as curtain walls.
A continuous wall for the basement of a building must not only support the building but
also provide a waterproof barrier capable of resisting the lateral force of the soil on the
outside. Curtain walls are also continuous in nature but, because they are installed in a
trench in the soil, they are not usually subjected to appreciable lateral forces and do not
need to be waterproof. Curtain walls may be constructed, after which the earth can be
backfilled on both sides, or they can be made of concrete poured directly into a narrow
trench. Curtain walls are strong, relatively watertight and give good protection against
rodents and other vermin.
2. Pier foundations are often used to support the timber frames of light buildings with no
suspended floors. They require much less excavation and building material. The stone or
concrete piers are usually set on footings. However, for very light buildings, the pier may
 take the form of a precast concrete block set on firm soil a few centimetres below ground
level. The size of the piers is often given by the weight required to resist wind uplift of the
whole building.
3. Pad and pole foundations consist of small concrete pads poured in the bottom of holes,
which support pressure-treated poles. The poles are long enough to extend and support the
roof structure. This is probably the least expensive type of foundation and is very
satisfactory for light buildings with no floor loads and where pressure-treated poles are
available.
4. A floating slab or raft foundation consists of a poured-concrete floor in which the outer
edges are thickened to between 20 cm and 30 cm and reinforced. This is a simple system
for small buildings that must have a secure joint between the floor and the sidewalls.
5. A pier and ground-level beam foundation is commonly used where extensive filling has
been necessary and the foundation would have to be very deep in order to reach
undisturbed soil. It consists of a reinforced concrete beam supported on piers. The piers
need to be deep enough to reach undisturbed soil and the beam must be embedded in the
soil deeply enough to prevent rodents from burrowing under it. For very light buildings
such as greenhouses, timber ground-level beams may be used.
6. Piles are long columns that are driven into soft ground where they support their load by
friction with the soil rather than by a firm layer at their lower end. They are seldom used
for farm buildings.
Foundation materials
The foundation material should be at least as durable as the rest of the structure. Foundations
are subject to attack by moisture, rodents, termites and, to a limited extent, wind. The moisture
may come from rain, surface water or groundwater and, although a footing drain can reduce
the problem, it is important to use a foundation material that will not be damaged by water or
the lateral force created by saturated soil on the outside of the wall. In some cases, the
foundation must be watertight in order to prevent water from penetrating into a basement or up
through the foundation and into the building walls above. Any foundation should be continued
for at least 150 mm above ground level to give adequate protection to the base of the wall from
moisture, surface water, etc.
Stones
Stones are strong, durable and economical to use if they are available near the building site.
Stones are suitable for low piers and curtain walls, where they may be laid up without mortar
if economy is a major factor, although it is difficult to make them watertight, even if laid with
mortar. Also, it is difficult to exclude termites from buildings with stone foundations because
of the numerous passages between the stones. However, laying the top course or two in good,
rich mortar and installing termite shields can overcome the termite problem to a large degree.
Earth
The primary advantage of using earth as a foundation material is its low cost and availability.
It is suitable only in very dry climates. Where rainfall and soil moisture are too high for an
unprotected earth foundation, they may be faced with stones or shielded from moisture with
polythene sheet.
Poured concrete
Concrete is one of the best foundation materials because it is hard, durable and strong in
compression. It is not damaged by moisture and can be made nearly watertight for basement
walls. It is easy to cast into the unique shapes required for each foundation.
Concrete blocks
Concrete blocks may be used to construct attractive and durable foundation walls. The forms
required for poured-concrete walls are unnecessary and, because of their large size, concrete
blocks will lay up faster than bricks. A block wall is more difficult to make watertight than a
concrete wall and does not resist lateral forces as well as a poured-concrete wall.
Bricks
Stabilized earth bricks or blocks have the same inherent restrictions as monolithic earth
foundations. They are suitable only in very dry areas and even there they need protection from
moisture. Adobe bricks are too easily damaged by water or ground moisture to be used for
foundations. Locally made burnt bricks can often be obtained at low cost, but only the best
quality bricks are satisfactory for use in moist conditions. Factory made bricks are generally
too expensive to be used for foundations.
Plinth Beam
Plinth beam is a beam structure constructed either at or above the ground level to take up the
load of the wall coming over it.
Plinth
The plinth is constructed above the ground level. It is a cement-mortar layer lying between the
substructure and the superstructure.
Damp Proof Course (DPC)
Damp proof course (DPC) is generally applied at basement levels which restricts the movement
of moisture through walls and floors. Selection of materials for damp proof course and its
various methods of applications in buildings is discussed below.
Materials for Damp Proof Course (DPC)
Properties of Materials for DPC
An effective damp proofing material should have the following properties;
1. It should be impervious.
2. It should be strong and durable, and should be capable of withstanding both dead as
well as live loads without damage.
3. It should be dimensionally stable.
4. It should be free from deliquescent salts like sulphates, chlorides and nitrates.
Types of Materials for Damp Proof Course
The materials commonly used to check dampness can be divided into the following three
categories:
 Flexible Materials: Materials like bitumen felts (which may be hessian based or
fiber/glass fiber based), plastic sheeting (polythene sheets) etc.
 Semi-rigid Materials: Materials like mastic, asphalt, or combination of materials or
layers.
 Rigid Materials: Materials like first class bricks, stones, slate, cement concrete etc.
Selection of Materials for Damp Proof Course in Buildings
The choice of material to function as an effective damp proof course requires a judicious
selection. It depends upon the climate and atmospheric conditions, nature of structure and the
situation where DPC is to be provided.
The points to be kept in view while making selection of DPC materials are briefly discussed
below:
1. DPC above ground level
For DPC above ground level with wall thickness generally not exceeding 40 cm, any one of
the type of materials mentioned above may be used. Cement concrete is however commonly
adopted material for DPC at plinth level, 38 to 50mm thick layer of cement concrete M15
(1:2:4 mix) serves the purpose under normal conditions.
In case of damp and humid atmosphere, richer mix of concrete should be used. The concrete
is further made dense by adding water proofing materials like Pudlo, Impermo, Waterlock
etc. in its ingredients during the process of mixing. It is used to apply two coats of hot
bitumen over the third surface of the concrete DPC.
2. DPC Material for floors, roofs etc.
For greater wall thickness or where DPC is to be laid over large areas such as floors, roofs,
etc., the choice is limited to flexible materials which provide lesser number of joints like
mastic, asphalt, bitumen felts, plastic sheets etc.
The felts when used should be properly bonded to the surface with bitumen and laid with
joints properly lapped and sealed.
3. DPC Material for situations where differential thermal movements occur
In parapet walls and other such situations, materials like mastic, asphalt, bitumen felts and
metal (copper or lead) are recommended.
It is important to ensure that the DPC material is flexible so as to avoid any damage or
puncture of the material due to differential thermal movement between the material of the
roof and the parapet.
4. DPC material for Cavity Walls
In cavity wall construction, like cavity over the door or window should be bridged by flexible
material like bitumen felt, strips or lead etc.
SUPERSTRUCTURE
The superstructure is the portion of a building which is constructed above the ground level and
it serves the purpose of structure’s intended use. It includes columns, beams, slab upwards
including all finishes, door and window schedules, flooring, roofing, lintels, and parapets.
1. Lintels
Lintels are constructed above the wall openings like doors, windows, etc. These structures
support the weight of the wall coming over the opening. Normally, lintels are constructed by
reinforced cement concrete. In residential buildings, lintels can be either constructed from
concrete or from bricks.
Lintels are classified based on the material of construction as:
1. Timber Lintel
In olden days of construction, Timber lintels were mostly used. But nowadays they are replaced
by several modern techniques, however in hilly areas these are still used. The main
disadvantages with timber are more cost and less durable and vulnerable to fire. If the length
of opening is more, then it is provided by joining multiple number of wooden pieces with the
help of steel bolts which was shown in fig (a). In case of wider walls, it is composed of two
wooden pieces kept at a distance with the help of packing pieces made of wood. Sometimes,
these are strengthened by the provision of mild steel plates at their top and bottom, called as
flitched lintels.

2. Stone Lintel
These are the most common type, especially where stone is abundantly available. The thickness
of these are most important factor of its design. These are also provided over the openings in
brick walls. Stone lintel is provided in the form of either one single piece or more than one
piece. The depth of this type is kept equal to 10 cm / meter of span, with a minimum value of
15 cm. They are used up to spans of 2 meters. In the structure is subjected to vibratory loads,
cracks are formed in the stone lintel because of its weak tensile nature. Hence caution is needed.
3. Brick Lintel
These are used when the opening is less than 1m and lesser loads are acting. Its depth varies
from 10 cm to 20 cm, depending up on the span. Bricks with frogs are more suitable than
normal bricks because frogs when filled with mortar gives more shear resistance of end joints
which is known as joggled brick lintel.

4. Reinforced Brick Lintel

These are used when loads are heavy and span is greater than 1m. The depth of reinforced brick
lintel should be equal to 10 cm or 15 cm or multiple of 10 cm. the bricks are so arranged that
2 to 3 cm wide space is left length wise between adjacent bricks for the insertion of mild steel
bars as reinforcement. 1:3 cement mortar is used to fill up the gaps.
Vertical stirrups of 6 mm diameter are provided in every 3rd vertical joint. Main reinforcement
is provided at the bottom consists 8 to 10 mm diameter bars, which are cranked up at the ends.
5. Steel Lintel
These are used when the superimposed loads are heavy and openings are large. These consist
of channel sections or rolled steel joists. We can use one single section or in combinations
depending up on the requirement.
When used singly, the steel joist is either embedded in concrete or cladded with stone facing
to keep the width same as width of wall. When more than one units are placed side by side,
they are kept in position by tube separators.

6. Reinforced Cement Concrete Lintel

At present, the lintel made of reinforced concrete are widely used to span the openings for
doors, windows, etc. in a structure because of their strength, rigidity, fire resistance, economy
and ease in construction. These are suitable for all the loads and for any span. The width is
equal to width of wall and depth depends on length of span and magnitude of loading.
Main reinforcement is provided at the bottom and half of these bars are cranked at the ends.
Shear stirrups are provided to resist transverse shear as shown in fig. below.
R.C.C lintel over a window with projection is displayed in below fig.

R.C.C boot lintels are provided over cavity walls. These will give good appearance and
economical. A flexible D.P.C is provided above as shown in fig.

2. Beams and slabs

Beams and slabs form the horizontal members in a building. For a single storey building, the
top slab forms the roof. In case of a multi-storey building, the beam transfers the load coming
from the floor above the slab which is in turn transferred to the columns. Beams and slabs are
constructed by reinforced cement concrete (R.C.C).
Types of Beams in Construction
Different types of beams are used in construction of building and structures. These are
horizontal structural element that withstand vertical loads, shear forces and bending moments.
Beams transfer loads imposed along their length to their end points to walls, columns,
foundations, etc.
There are different types of beams which are classified based on the following conditions
 Based on Support Conditions
 Based on Construction Materials
 Based on Cross-Section Shapes
 Based on Geometry
 Based on Equilibrium Condition
 Based on Method of Construction
 Others
Based on Support Conditions
1. Simply Supported Beam
It is the one of the simplest structural elements that both ends are rest on supports but are free
to rotate. It contains pinned support at one end and roller support at the other end. On the basis
of assign load, it sustains shearing and bending.

Fig. 1: Simply supported beam

2. Fixed Beam
It is supported at both ends and fixed to resist rotation. It is also called a built-in beam. The
fixed ends produce fixing moments other than the reactions.

Fig. 2: Fixed beam

3. Cantilever Beam
If a beam is fixed at one end and set to be free at the end, it is termed as cantilever beam. The
beam distributes the load back to the support where it is forced against with a moment and
shear stress. Cantilever beams allow the creation of a bay window, balconies, and some bridges.
Fig. 3: Cantilever beam
4. Continuous Beam
A continuous beam has more than two supports distributed along its entire length.

Fig. 4: Continuous beam

Based on Construction Materials
1. Reinforced Concrete Beams
It is constructed from concrete and reinforcement as shown in Fig. 5.

Fig. 5: Reinforced concrete beam

6. Steel Beams

It is constructed from steels and used in several applications.

Fig. 6: Steel beam

7. Timber beams

This type of beam is constructed from timber and used in the past, but its application is
significantly declined now.

Fig. 7: Timber Beam

8. Composite Beams

Composite beams are constructed from two or more different types of materials such as steel
and concrete, and various valid cross sections have been utilized as shown in fig.8.

Fig. 8: Composite beam

Based on Cross-Section Shapes

Several cross sectional shapes of beams are available and used in different parts of of
structures. These beams can be constructed from reinforced concrete, steel, or composite
materials.
Reinforced concrete cross sectional shapes include:

Rectangular beam

This type of beam is widely used in the construction of reinforced concrete buildings and
other structures.

Fig. 9: Rectangular Reinforced concrete beam

T-section beam

This type of beam is mostly constructed monolithically with reinforced concrete slab.
Sometimes, Isolated T-beam are constructed to increase the compression strength of concrete.
Added to that, inverted T-beam can also be constructed according to the requirements of
loading imposed.
Fig. 10: T-beam Fig. 11: Inverted T-beam

L-section beam
This type of beam is constructed monolithically with reinforced concrete slab at the perimeter
of the structure, as illustrated in Fig. 10.
Steel cross sectional shapes include:

There are various steel beam cross sectional shapes. Each cross sectional shape offer superior
advantages in a given conditions compare with other shapes.
Square, rectangular, circular, I-shaped, T-shaped, H-shaped,C-shaped, and tubular are
examples of beam cross sectional shapes
constructed from steel.
Fig. 12: Steel beam cross sectional shapes

Different types of beams based on cross sectional shapes constructed from composite
materials are shown in Fig. 8.

Based on Geometry

12. Straight beam

Beam with straight profile and majority of beams in structures are straight beams.

Fig. 13: straight beam

13. Curved beam

Beam with curved profile, such as in the case of circular buildings.

Fig. 14: Curved beam

14. Tapered beam

Beam with tapered cross section.

Fig. 15: Tapered beam

5. Based on Equilibrium Condition

15. Statically determinate beam

For a statically determinate beam, equilibrium conditions alone can be used to solve
reactions, i.e the number of unknown reactions are equal to the the number of equations.

Fig. 16: Statically determinate beam

16. Statically indeterminate beam

For a statically indeterminate beam, equilibrium conditions are not enough to solve reactions.
So, the analysis of this type of beam is more complicated than that of statically determinate
beams.
Fig. 17: statically indeterminate beam

Based on Method of Construction

17. Cast In-situ Concrete Beam
This type of beam is constructed on project site. so, forms are initially fixed then fresh
concrete is poured and allowed to be hardened. Then, loads will be imposed.

Fig. 18: Cast in situ beam

18. Precast Concrete Beam

This type of beam is manufactured in factories. So, the construction condition is more
controllable compare with on-site construction. Consequently, the quality of concrete of the
beam will be greater. Various cross sectional shapes can be manufactures such as T- beam,
Double T-beam, Inverted T-beam and many more.

Fig. 19: Precast concrete beam

19. Prestressed Concrete Beam
This type of beam constructed by stressing strands prior to applying loads on the beam. Pre-
tensioned Concrete beam and post-tensioned Concrete Beam are variations of pre-stressed
concrete beam.

Fig. 20: Prestressed concrete beam

Others

20. Deep Beam

beams that have large depths, and its clear span to depth ratio is less than 4 according to ACI
Code. Significant amount of the load is carried to the supports by a compression force
combining the load and the reaction. Consequently, the strain distribution is no longer
considered linear as in the case of conventional beams.
Fig. 21: Deep beam

21. Girder

Beams that take heavy loads, generally steel sections are used.

Fig. 22: Girder

Concrete Slab Types

A reinforced concrete slab is a crucial structural element and is used to provide flat
surfaces(floors and ceilings) in buildings. On the basis of reinforcement provided, beam
support, and the ratio of the spans, slabs are generally classified into one-way slab and two-
way slab. The former is supported on two sides and the ratio of long to short span is greater
than two. However, the latter is supported on four sides and the ratio of long to short span is
smaller than two.
Varying conditions and stipulations ask for the selection of appropriate and cost-effective
concrete slab, keeping in view, the type of building, architectural layout, aesthetic features, and
the span length. Concrete slabs, therefore, are further classified into: one-way joist slab, flat
slab, flat plate, waffle slab, hollow core slab, precast slab, slabs on grade, hardy slab, and
composite slab.
1. One-Way Slabs on Beams

Cast in situ method is used to construct one-way slabs on beams which involves fixing of forms
followed with the installation of reinforcements, and finally the pouring of fresh concrete.
One-way slabs on beams are most suitable for spans of 3-6m, and a live load of 3 to 5KN/m 2.
They can also be used for larger spans with relatively higher cost and higher slab deflection.
Additional formwork for the beams is however needed.

Fig. 1: One-way Slab on Beams

2. One-way joist slab (Ribbed slab)

It consists of a floor slab, usually 50 to 100mm thick, supported by reinforced concrete ribs (or
joists). The ribs are usually tapered and are uniformly spaced at distances that do not exceed
750mm. The ribs are supported on girders that rest on columns.
A one-way joist concrete slab is suitable for spans of 6-9m and live loads of 4-6KN/m2.
Because of the deep ribs, the concrete and steel quantities are relatively low, but expensive
formwork is needed.

Fig. 2: One-way Ribbed Slab

3. Waffle Slab (Grid slab)

It is a type of reinforced concrete slab that contains square grids with deep sides. Waffle slab
construction process includes fixing forms, placement of pods on shuttering, installation of
reinforcement between pods, installation of steel mesh on top of pods, and pouring of concrete.
Grid slabs are suitable for spans of 9-15m and live loads of 4-7KN/m2. Formwork, including
the use of pans, is quite expensive.

Fig. 3: Waffle Slab

4. Flat Plates

Flat plates can be constructed as one-way or two-way slabs and it is directly supported by
columns or walls. It is easy to construct and requires simple formworks.
Flat plates are most suitable for spans of 6 to 8m, and live loads between 3 and 5KN/m 2. Added
to that, the range of spans for pre-stressed flat plates is between 8-12m, and it can also be
constructed as post-tensioned slabs.
The advantages of adopting flat plates include low-cost formwork, exposed flat ceilings, and
faster construction. Flat plates have low shear capacity and relatively low stiffness, which may
cause noticeable deflection.
Fig. 4: Flat Plate

5. Flat Slabs

This is typically a reinforced slab supported directly by columns or caps, without the use
of beams. This type of slab is generally easy to construct and requires little formwork. The
loads are directly transferred to the columns.
Flat slabs are most suitable for spans of 6 to 9m, and for live loads of 4-7KN/m2. They need
more formwork than flat plates, especially for column capitals. In most cases, only drop panels
without column capitals are used. It can be constructed as post-tensioned flat slabs.

Fig. 5: Flat Slab

6. Two-way Slabs on Beams

The construct of this type of slab is similar to that of one-way slab on beams, but it may need
more formworks since two-way slabs are supported on all sides. Slabs on beams are suitable
for spans between 6 and 9m, and live loads of 3-6KN/m2 . The beams increase the stiffness of
the slabs, producing relatively low deflection. Additional formwork for the beams is needed.

Fig. 6: Two-way Slab on Beams

7. Hollow core slab

It is a type of precast slab through which cores are run. Not only do these cores decline slab
self-weight and increase structural efficiency but also act as service ducts. It is suitable for
cases where fast constructions are desired.
There is no restriction on the span of the hollow core slab units, and their standard width is
120mm and depth ranges from 110mm to 400mm.
The slab units are commonly installed between beams using cranes and the gaps between units
are filled with screeds. It has been observed that, hollow core slab can support 2.5 kN/m2 over
a 16m span. It is suitable for offices, retail or car park developments.
Fig. 7: Hollow Core Slab

8. Hardy Slab

It is constructed using hardy bricks which significantly decline the amount of concrete and
eventually the slab’s self-weight. The thickness of hardy slab is commonly greater than
conventional slab and around 270mm.
The construction of hardy slab involves formwork installation, hardy block placement,
placement of reinforcement into gaps between blocks, placement of steel mesh on the blocks,
and finally pouring of concrete.
It is economical for spans of length up to 5m, and it reduces the quantity of concrete below
neutral axis, and moderate live loads shall be imposed. It is constructed at locations where the
temperatures are very high. The application of this type of slab can be seen in Dubai and China.

Fig. 8: Hardy Block

Fig. 9: Hardy Slab Construction

9. Bubble Deck Slab

It is constructed by placing plastic bubbles which are prefabricated and the reinforcement is
then placed between and over plastic bubbles and finally, fresh concrete is poured. The plastic
bubbles replace the ineffective concrete at the center of the slab.
Bubble Deck slabs reduce weight, increase strength, larger spans can be provided, fewer
columns needed, no beams or ribs under the ceiling are required. Consequently, not only does
it decline the total cost of construction but is also environmentally friendly since it reduces
amount of concrete.
Fig. 10: Bubble Deck Slab Types

Fig. 11: Bubble Deck Slab

10. Composite Slab

Commonly, it is constructed from reinforced concrete cast on top of profiled steel decking. The
decking acts as formwork and working area during the construction phase, and it also acts as
external reinforcement during service life of the slab.
For a steel decking of thickness between 50-60mm, the span of the slab can reach up to 3m.
However, if the steel decking thickness is increased up to 80mm, slabs with span of 4.5m can
be constructed.

Fig. 12: Composite Slab

11. Precast Slab

Precast concrete slabs are casted and cured in manufacturing plants, and then delivered to the
construction site to be erected. The most outstanding advantage of the preparation of slabs in
manufacturing plants is the increase in efficiency and higher quality control which may not be
achieved on site.
The most commonly used precast slabs are: the channel and double-T types. They can be used
for spans up to 15m. The double-T slabs vary in sizes and spans up to 15m have been used.
The tongue-and-groove panel could vary in size based on the design requirement. When they
are placed, the tongue of one panel is placed inside the groove of adjacent panel.
With regard to the cost of precast slabs, it is reported that precast concrete slabs are cheaper
than cast in situ concrete slab by approximately 24%.

Fig. 13: Precast Slab

12. Slab on grade

The slab which is casted on the surface of the earth is called a Ground slab. Generally, slab
on grade are classified into three types:
1. Slab on ground

It is the simplest type of slab on grade which is a composite of stiffening beams constructed
from concrete around perimeter of the slab, and has a slab thickness of 100mm. It is suitable
for stable ground which is mostly composed of sand and rock and not influenced by moisture,
and soils that undergo slight movement due to moisture.

2. Stiffened raft slab

It is similar to slab on ground apart from stiffening beams which are set in channels through
the middle of the slab. Consequently, it creates a kind of supporting grid of concrete on the
base of the slab. Soil with moderate, high amount, and severe movement due to moisture.

3. Waffle raft slab

It is constructed entirely above the ground by pouring concrete over a grid of polystyrene
blocks known as ‘void forms’. Waffle raft slabs are generally suitable for sites with less reactive
soil, use about 30% less concrete and 20% less steel than a stiffened raft slab, and are generally
cheaper and easier to install than other types. These types of slabs are suitable only for very
flat ground.

Fig. 12: Types of Slabs on Ground

Columns

Columns can be of two types: Architectural columns and structural columns. Architectural
columns are constructed to improve the building’s aesthetics while a structural column takes
the load coming from the slab above and transfers safely to the foundation.

There are several types of structural columns which are used in different parts of structures. A
column is a vertical structural member that carry loads mainly in compression. It might transfer
loads from a ceiling, floor slab, roof slab, or from a beam, to a floor or foundations. Commonly,
columns also carry bending moments about one or both of the cross-section axes.

Types of Columns in Buildings

Columns are classified based on the several conditions which include:
1. Based on Types of Reinforcement
2. Based on Types of Loading
3. Based on Slenderness Ratio
4. Based on Shape
5. Based on Construction Material

Based on Types of Reinforcement

1. Tied Column
This type of column is commonly construction from reinforced concrete. Longitudinal
reinforcement are confined within closely spaced tie reinforcement. It is estimated that 95% of
all columns in buildings are tied.

Fig. 1: Tied column

2. Spiral Column
Spiral column is also construction from reinforced concrete. In this type of column,
longitudinal bars are confined within closely spaced and continuously wound spiral
reinforcement.
Spiral reinforcement provide lateral restrains (Poisson’s effect) and delays axial load failure
(ductile).
Fig. 2: Spiral Column
3. Composite column
When the longitudinal reinforcement is in the form of structural steel section or pipe with or
without longitudinal bars, it is called as a composite column.
This type of column have high strength with fairly small cross section, in addition to exhibit
good fire performance.

Fig. 3: Composite column

Based on Types of Loading
4. Axially Loaded Column
If vertical axial loads act on the center of gravity of the cross-section of the column, then it is
termed as axially loaded column.
Axially loaded column is rare in construction since coinciding vertical loads on the center of
gravity of column cross section is not practical.
Interior column of multi-storey buildings with symmetrical loads from floor slabs from all sides
is an example of this type of column.

Fig. 4: Axially loaded column

5. Column with Uniaxial Eccentric Loading

When vertical loads do not coincide with center of gravity of column cross section, but rather
act eccentrically either on X or Y axis of the column cross section, then it is called uniaxially
eccentric loading column.
Column with uniaxial loading are generally encountered in the case of columns rigidly
connected beam from one side only such as edge columns.

Fig. 5: Column with uniaxial eccentric loading

6. Column with Biaxial Eccentric Loading
When vertical on the column is not coincide with center of gravity of column cross section and
does not act on either axis (X and Y axis), then the column is called biaxially eccentric loaded
column.
Columns with biaxial loading is common in corner columns with beams rigidly connected at
right angles at the top of columns.

Fig. 6: Column with biaxial eccentric loading

Based on Slenderness Ratio
Based on slenderness ratio, (effective length/ least lateral dimension), columns are
categorized as follow:

6. Short Column
If the ratio effective length of the column to the least lateral dimension is less than 12, the
column is called as the short column. A short column fails by crushing (pure compression
failure).
Fig. 7: Short column
7. Long Column
If the ratio effective length of the column to the least lateral dimension exceeds 12, it is called
as long column. A long column fails by bending or buckling.

Fig. 8: Long column

Based on Shape
Shape of Reinforced Concrete Column

8. Square or Rectangular Column

They are generally used in the construction of buildings. It is much easier to construct and cast
rectangular or square columns than circular ones because of ease of shuttering and to support
it from collapsing due to pressure while the concrete is still in flowable form.

Fig. 9: Square column

9. Circular column
They are specially designed columns, which are mostly used in piling and elevation of the
buildings.
Fig. 10: Circular column
10. L-Shape Column
Commonly, L-shaped column is utilized in the corners of the boundary wall and has similar
characteristics of a rectangular or square column.

Fig. 11: L-shaped column

11. T-Shape column
It is utilized based on design requirements of a structure. T-Shaped column is widely used in
the construction of bridges.

Fig. 12: T-shaped column

12. Shape of Steel Column

There are different standard and built up shape of steel columns which are shown in Fig. and
Fig. Common shapes of steel columns include I, channel, equal angle, and T-shape.
Fig. 13: Steel column cross section shape (Standard)

Fig. 14: Steel column cross section shape (built up)

13. Shape of Composite Column

The usual shape of composite columns are shown in Fig.

Fig. 15: Composite column shape

Based on Construction Material

Types of columns based on construction materials include
Reinforced Concrete, Steel, timber, Brick, Block, and Stone Column.
Fig. 16: Types of Column; A-reinforced concrete, B- steel, C-timber, D-brick, E-block, and
F-stone

Walls

Walls may be divided into two types:

(a) Load-bearing walls that support loads from floors and roof in addition to their own weight
and resist side-pressure from wind and, in some cases, from stored material or objects within
the building.

(b)Non-load-bearing walls that carry no floor or roof loads.

Each type may be further divided into external or enclosing walls, and internal dividing walls.
The term ‘partition’ is applied to walls, either load-bearing or non-load-bearing, that divide
the space within a building into rooms. Good-quality walls provide strength and stability,
weather resistance, fire resistance, thermal insulation and acoustic insulation.
Types of building wall

While there are various ways to construct a wall and many different materials can be used,
walls can be divided into four main groups.

1. Masonry walls, where the wall is built of individual blocks of materials such as brick,
clay, concrete block or stone, usually in horizontal courses bonded together with
some form of mortar. Several earth-derived products, either air-dried or fired, are
reasonable in cost and well suited to the climate.
2. Monolithic walls, where the wall is built of a material placed in forms during
construction. The traditional earth wall and the modern concrete wall are examples.
Earth walls are inexpensive and durable if placed on a good foundation and protected
from rain by rendering or wide roof overhangs.
3. Frame walls, where the wall is constructed as a frame of relatively small members,
usually of timber, at close intervals, which, together with facing or sheathing on one
or both sides, form a load-bearing system. Offcuts are a low-cost material to use for a
frame-wall covering.
4. Membrane walls, where the wall is constructed as a sandwich of two thin skins or
sheets of reinforced plastic, metal, asbestos cement or other suitable material bonded
to a core of foamed plastic to produce a thin wall element with high strength and low
weight. Another form of construction suitable for framed or earth buildings consists
of relatively light sheeting secured to the face of the wall to form the enclosed
element. These are generally termed ‘claddings’.

Factors that determine the type of wall to be used are:

• the materials available at a reasonable cost;

• the availability of craft workers capable of using the materials in the best way;
• climate;
• the use of the building and functional requirements.
The height of walls should allow people to walk freely and work in a room without
knocking their heads on the ceiling, beams, etc. In dwellings with ceilings, 2.4 metres is
 a suitable height. Low roofs or ceilings in a house create a depressing atmosphere and
tend to make the rooms warmer in hot weather.

Stairs and ladders

The angle, which is governed by the height and the horizontal distance available, will
determine the most suitable means of moving from one level to another. • For a slope up to
1:8 (7°), a ramp is suitable for both walking and pushing a wheelbarrow. • For walking alone,
a 1:4 (14°) slope is satisfactory provided that it remains permanently dry. • For slopes
between 1:3 and 1:0.8 (18° to 50°), stairways are possible, although 30° to 35° is preferred.
Angles steeper than 50° require a ladder or ladder-stairway. • Temporary ladders should be
set up at 60° to 75°, while a fixed ladder may be vertical if necessary.

Ramps: Ramps may be made of tamped earth or concrete. An earth ramp should be made of a
mixture of fine gravel and clay: the gravel to give texture for a nonslip surface and the clay to
serve as a binder. The surface of a ramp constructed of concrete should be ‘broomed’ across
its slope after having been poured and struck off.

A stair is a sequence of steps that connects different floors in a building structure. The space
occupied by a stair is called as the stairway. There are different types of stairs like a wooden
stair, R.C.C stair etc.

Stairs are designed to be either fixed to a wall with one outer stringer, fixed between walls, or
freestanding, with the majority of stairways having one wall stringer and one outer stringer.
The wall stringer is fixed directly to the wall along its entire length or is fixed to timber
battens plugged to the wall. The outer stringer is supported at both ends by the posts. The
posts also serve as the termination point for handrails that span between them. The space
between the handrail and the tread may be filled with balusters, balustrade or a solid panel to
improve both the safety and the appearance of the stairway. Reinforced concrete is better
suited for outdoor stairs than timber. The number, diameter and spacing of the main and
distribution reinforcement for each stairway must always be calculated by an experienced
designer.
Comfort in the use of stairs depends largely on the relative dimensions of the rise and going
of the steps.

Ladder-stairway: The recommended pitch for this type of steep, narrow stairway is 60°. The
width is usually roughly the minimum of 600 mm. The size of the going (tread) is dependent
on the pitch.

Timber ladders are basically of two types:

1. those having round rungs fixed in holes in the stringers;

2. those having square, or slightly rectangular, treads cut into and nailed on the forward side
of the stringers.

Ladders that are moved from place to place should have hooks and dowels so that they can be
thoroughly stabilized at the bottom and top. Ladders mounted permanently should be firmly
secured in their position and, if necessary, provided with handrails.

Roofs

A roof is an essential part of any building, in that it provides the necessary protection from rain,
sun, wind, heat and cold. The integrity of the roof is important for the structure of the building
itself, as well as for the occupants and the goods stored within the building.
The roof structure must be designed to withstand the dead load imposed by the roofing and
framing, as well as the forces of wind and, in some areas, snow or drifting dust. The roofing
must be leakproof and durable and may have to satisfy other requirements such as fire-
resistance, good thermal insulation or a high thermal capacity.
There is a wide variety of roof shapes, frames and coverings from which to choose. The choice
is related to factors such as the size and use of the building, its anticipated life and appearance,
and the availability and cost of materials. Roofs may be classified in three ways, according to:
1. The plane of the surface, i.e. whether it is horizontal or pitched.
2. The structural principles of the design, i.e. the manner in which the forces set up by external
loads is resolved within the structure.
3. The span.

Flat and pitched roofs: A roof is called a flat roof when the outer surface is within 5° of
horizontal, whereas a pitched roof has a slope of more than 5° in a c d f b 174 Rural structures
in the tropics: design and development one or more directions. Climate and covering material
affect the choice of a flat or pitched roof. The effect of climate is less marked architecturally
in temperate areas than in areas with extremes of climate. In hot, dry areas, the flat roof is
common because it is not exposed to heavy rainfall and it forms a useful outdoor living room.
In areas of heavy rainfall, a steeply pitched roof drains off rainwater more rapidly.
Two-dimensional roof structures have length and depth only, and all forces are resolved within
a single vertical plane. Rafters, roof joists and trusses fall into this category. They fulfil only a
spanning function, and volume is obtained by using several two-dimensional members carrying
secondary two-dimensional members (purlins) to cover the required span.
Three-dimensional structures have length, depth and also breadth, and forces are resolved in
three dimensions within the structure. These forms can fulfil a covering, enclosing and
spanning function and are now commonly referred to as ‘space structures’. Threedimensional
or space structures include cylindrical and parabolic shells and shell domes, multicurved slabs,
folded slabs and prismatic shells, grid structures such as space frames, and suspended or tension
roof structures
Long- and short-span roofs: Span is a major consideration in the design and choice of a roof
structure, although functional requirements and economy have an influence as well.
Short spans of up to 8 metres can generally be covered with pitched timber rafters or
lightweight trusses, either pitched or flat. Medium spans of 7–16 metres require truss frames
made of timber or steel.
Long spans of more than 16 metres should, if possible, be broken into smaller units.
Otherwise these roofs are generally designed by specialists using girder, space deck or
vaulting techniques.

In order to reduce the span and thereby reduce the dimensions of the members, the roof
structure can be supported by poles or columns within the building, or by internal walls.
However, in farm buildings, a freespan roof structure might be advantageous if the farmer
eventually wants to alter the internal arrangement of the building. The free space without
columns allows greater convenience in manoeuvring equipment as well.
Ring beam:
In large buildings that have block or brick walls, such as village stores, a 150 mm2 reinforced
concrete beam is sometimes installed on top of the external walls instead of a wall plate. The
objective of this ring beam, which is continuous around the building, is to carry the roof
structure in the event of part of the wall collapsing in an earth tremor. It also provides a good
anchorage for the roof, to prevent it lifting and to reduce the effects of heavy wind pressure on
the walls and unequal settlement.
Types of roof
1. Flat roof
The flat roof is a simple design for large buildings in which columns are not a disadvantage.
Although simple beams can be used for spans up to about 5 metres, with longer spans it is
necessary to use deep beams, web beams or trusses for adequate support.
The roof structure consists of the supporting beams, decking, insulation and a waterproof
surface. The decking, which provides a continuous support for the insulation and surface, can
be made of timber boards, plywood, chipboard, metal or asbestos-cement decking units or
concrete slabs. The insulation material improves the thermal resistance and is placed either
above or below the decking.
 2. Earth roof
Soil-covered roofs have good thermal insulation and a high capacity for storing heat. The
traditional earth roof is subject to erosion during rain, and requires regular maintenance to
prevent leakage. The roof is laid rather flat, with a slope of 1:6 or less. The supporting structure
should be generously designed of preservative-treated or termite-resistant timber or poles, and
should be inspected and maintained periodically because a sudden collapse of this heavy
structure could cause great harm. The durability of the mud cover can be improved by
stabilizing the top layer of soil with cement, and it can be waterproofed by placing a plastic
sheet under the soil.

However, the introduction of these improvements adds considerably to the cost of the roof.
Therefore, the improved earth roof is a doubtful alternative for lowcost roofing and should be
considered only in dry areas where soil roof construction is known and accepted.
3. Monopitch roof
Monopitch roofs slope in only one direction and have no ridge. They are easy to build,
comparatively inexpensive and recommended for use on many farm buildings. The maximum
span with timber members is about 5 metres, so wider buildings will require intermediate
supports. Also, wide buildings with this type of roof will have a high front wall, which increases
the cost and leaves the bottom of the high wall relatively unprotected by the roof overhang.
When using corrugated steel or asbestos-cement sheets, the slope should be not less than 1:3
(17° to 18°). A lower sloping angle may cause leakage, as strong winds can force water up the
slope.
4. Double-pitched (gable) roof
A gable roof normally has a centre ridge with a slope to either side of the building. With this
design, the use of timber rafters provides for a greater free span (7–8 metres) than a monopitch
roof. Although the monopitch design may be less expensive for building widths up to
10 metres, the inconvenience of many support columns favours the gable roof. The gable roof
may be built in a wide range of pitches to suit any of several types of roofing material.
5. Hip roof
A hip roof has a ridge in the centre and four slopes. Its construction is much more
complicated, requiring compound angles to be cut on all of the shortened rafters and
provision for deep hip rafters running from the ridge to the wall plate to carry the top ends of
the jack rafters. The tendency of the inclined thrust of the hip rafters to push out the walls at
the corners is overcome by tying the two wall plates together with an angle tie. At the hips
and valleys, the roofing material has to be cut at an angle to make it fit. The valleys are prone
to leakage, and special care has to be taken in the construction.
Four gutters are needed to collect the rainwater from the roof, but this does not necessarily
mean that there will be an increase in the amount of water collected. As this is an expensive
and difficult way to roof a building, it is only recommended in cases where it is necessary to
protect mud walls or unplastered brick walls against heavy driving rain and, for wide buildings,
to reduce the height of the end walls.

6. Conical roof
The conical roof is a three-dimensional structure that is commonly used in rural areas. It is easy
to assemble and can be built with locally available materials, making it inexpensive.
It must be constructed with a slope appropriate to the roofing materials to prevent it from
leaking. The conical roof design is limited to rather short spans and to either circular buildings
or to small, square buildings.
It does not allow for any extension. If modern roofing materials are used, there is considerable
waste because of the amount of cutting needed to secure a proper fit.
A conical roof structure requires rafters and purling and, in circular buildings, a wall plate in
the form of a ring beam.
This ring beam has three functions:
1. To distribute the load from the roof evenly to the wall.
2. To supply a fixing point for the rafters.
3. To resist the tendency of the inclined rafters to press the walls outwards radially by
developing tensile stress in the ring beam.
If the ring beam is properly designed to resist these forces and secondary ring beams are
installed closer to the centre, a conical roof can be used on fairly large circular buildings.
In the case of square buildings, the outward pressure on the walls from the inclined rafters
cannot be converted to pure tensile stress in the wall plate. This makes it more like the hip roof
structure and it should be designed with angle ties across the wall plates at the corners.

Roofing Materials
The roof shape, type of structure and slope determine the types of roofing material that are
suitable. The minimum slope on which a material can be used depends on exposure to the wind,
the type of joint and overlap, porosity and the size of the unit.
When considering the cost of various roofing materials, it should be noted that those requiring
steeper slopes will need to cover a greater area.
The weight of the roof-covering material influences greatly the design of the roof structure and
the purling.

 Thatch
Thatch is a very common roofing material in rural areas. It has good thermal insulation qualities
and helps to maintain reasonably uniform temperatures within the building, even when outside
temperatures vary considerably. The level of noise from rain splashing on the roof is low but,
during long, heavy rains, some leakage may occur. Although thatch is easy to maintain, it may
also harbour insects, pests and snakes.
A number of different plant materials, such as grass, reeds, papyrus, palm leaves and banana
leaves, are suitable and inexpensive when locally available.
Although the materials are cheap, thatching is rather labour-intensive and requires some skill.
The durability of thatch is relatively low. In the case of grass, major repairs will be required
every two to three years, but when thatch is laid well by a specialist and properly maintained,
it can last for 30 years or more. Although the supporting structure of wooden poles or bamboo
is simple, it must be strong enough to carry the weight of wet thatch.
The use of thatch is limited to rather narrow buildings because the supporting structure would
otherwise be complicated and expensive, and the rise of the roof would be very high owing to
the need for a very steep slope. Palm leaves should have a slope of at least 1:1.5 (but preferably
1:1) and grass thatch should have a minimum of 1:1 (but preferably 1:0.6). Increasing the slope
will improve durability and reduce the risk of leakage. The risk of fire is extremely high but
may be reduced by treating the thatch with a fireretardant.

 Galvanized corrugated steel sheets

Galvanized corrugated steel sheets (GCS) are the cheapest of the modern corrugated sheeting
materials and are widely used as roofing material for farm buildings. While uprotected steel
would have a very short life, a zinc coating (galvanizing) adds substantial protection at a
relatively low cost. Alternative coatings for steel sheets are bitumen, polyvinyl chloride
(plastic) on zinc, asbestos, felt and polyester. If the coating is damaged, the steel will rust.
When the first signs of rust appear, the sheet should be coated with a lead-based paint to stop
the rusting.
The main advantages of galvanized corrugated steel are:
1. Its relatively light weight makes the sheets easy to transport and flexible so they are not
easily damaged during transport.
2. It is easy to install and handle. However, the edges of the sheets are often very sharp and can
Chapter 8 – Elements of construction 183 cause cuts in clothing and skin. The sheets may be
cut to any required length, and the roofing nails can be driven through the sheets directly
without drilling holes.
3. The supporting structure can be relatively simple. Owing to the flexibility of the sheets,
minor movements of the supporting structure can occur without causing damage.
4. The sheets are quite durable if they are maintained and are not attacked by termites or fungus.
They are watertight and non-combustible.
5. They can be dismantled and reused, provided that the same nail holes are used.
The main disadvantages of GCS are its poor thermal properties and the noise caused by heavy
rainfall and thermal movements. The thermal and acoustic properties are improved by using an
insulated ceiling.

 Asbestos-cement sheets
The advantages of asbestos-cement sheets (A-C) compared with GCS sheets are:
1. Longer life if properly fitted.
2. Less noise from heavy rain and thermal movements.
3. More attractive.
4. Better thermal insulation properties.
The disadvantages are:
1. They are heavier (the weight per square metre is more than twice that of GCS), therefore it
is more expensive to transport and requires a stronger roof structure.
2. Brittleness causes a high rate of wastage from breakage during transport and installation. A
more rigid roof structure is necessary, as the sheet does not allow for more than very small
movements of the supporting structure without cracking. Walking on the roof may also cause
cracking.
3. They are labour-intensive because of weight and brittleness.
4. The corners of the sheets must be mitred prior to fitting, and holes for the fixing screws must
be drilled.
5. They become discolored easily with dust and algae.
6. The manufacture and processing of asbestos products presents hazards to health.
Corrugated asbestos-cement sheets are normally marketed in a variety of corrugations and
sizes.

 Corrugated aluminium sheets

Corrugated aluminium (CA) sheets are lighter and more durable than GCS sheets, but are more
expensive. When new, the sheets have a bright, reflective surface but, after a year or more,
oxidation of the surface will reduce the glare. There is never any need to paint aluminium sheets
for protection. The reflective surface will keep the building cooler than with GCS sheets but,
because aluminium is softer, the roof is more likely to tear away in a heavy wind storm.
Aluminium also has greater thermal expansion than steel, resulting in noisy creaks and more
stress on fasteners. Corrugated aluminium sheets are normally supplied with the same
corrugation and in the same sizes as GCS. For use in farm buildings, a thickness of 0.425 mm
is recommended. The sheets are laid and fixed in the same manner as GCS.

 Fibreglass-reinforced plastic sheets

These sheets are shaped like those of steel, asbestos cement or aluminium and are used to
replace some of the sheets in a roof to give overhead light. They are translucent and give good
light inside large halls, workshops etc. They are long-lasting, simple to install and provide
inexpensive light, although the sheets themselves are expensive. They are combustible and
must be cleaned occasionally.

 Roof tiles and slates

Tiles were originally handmade using burnt clay, but now they are manufactured by machine
from clay, concrete and stabilized soil in several sizes and shapes. Plain tiles are usually
cambered from head to tail so they do not lie flat on each other. This prevents capillary
movement of water between the tiles. The shaped side lap in single-lap tiling takes the place of
the double end lap and bond in plain tiles or slates. Many types of single-lap tile are available,
examples of which are shown in Figure 8.59. Slates were originally made from natural stone,
but now they are also manufactured from asbestos-cement and sisal-cement. As plain tiles and
slates have similar properties and are laid and fixed in the same manner, they will be discussed
together. Tiles and slates are durable, require a minimum of maintenance and have good
thermal and acoustic properties. The units themselves are watertight, but leaks may occur
between the units if they are not laid properly. However, handmade tiles tend to absorb water,
and stabilized-soil tiles may erode in heavy rains. While they are fairly easy to lay and fix,
being very heavy, they require a very strong supporting roof structure. However, the weight is
advantageous in overcoming uplifting wind forces. The dead weight of the covering will
normally be enough anchorage for the roofing, as well as the roof structure.

 Wood shingles
Wood shingles are pleasing in appearance and, when made from decay-resistant species, will
last for between 15 and 20 years, even without preservative treatment. Cedar and cypress will
last 20 years or more. Wood shingles have good thermal properties and are not noisy during
heavy rain. The shingles are light and not very sensitive to movements in the supporting
structure, which means that a rather simple roof frame made of round timber can be used.

 Bamboo shingles
The simplest form of bamboo roof covering is made of halved bamboo culms running full
length from the eaves to the ridge. Large-diameter culms are split into two halves and the cross-
section at the nodes removed. The first layer of culms is laid side by side with the concave face
upwards. The second is placed over the first with the convex face upwards. In this way, the
bamboo overlaps in the same way as in a tile roof, and can be made completely watertight.
Several types and shapes of bamboo shingle roofing may be used where only smaller sizes of
bamboo culm are available.
Rainwater drainage from roofs
The simplest method is to let the roof water drop onto a splash apron all around the building.
This method also protects the walls from surface groundwater. The water is then collected in a
concrete ground channel, or allowed to flow onto the ground surrounding the building to soak
into the soil. This method can only be recommended for very small buildings because the
concentrated flow from a larger building may cause considerable soil erosion and damage to
the foundation. The water from ground channels is drained into a soakaway or collected and
stored. Blind channels are frequently used. These are simply trenches filled with stones that act
as soakaways, either for a ground channel or for a splash apron. Pitched roofs are often provided
with eave gutters to collect and carry the rainwater to downpipes that deliver the water to
ground drains or a tank. Flat roofs are usually constructed with a slight fall to carry rainwater
directly to a roof outlet.
The sizing of gutters and downpipes to effectively remove rainwater from a roof will depend
upon the:
1. Area of the roof to be drained.
2. Anticipated intensity of rainfall.
3. Material of the gutter and downpipe.
4. Fall along the gutter, usually in the range of 1:150 to 1:600.
5. Number, size and position of outlets.
6. Number of bends: each bend will reduce the flow by 10–20 percent.
Pitched roofs receive more rain than their plan area would indicate, owing to the wind blowing
rain against them. An estimate of the effective area for a pitched roof can be made by
multiplying the length by the horizontal width, plus half the rise.
There is always a possibility that unusually heavy rain, or a blockage in a pipe, will cause
gutters to overflow. With this in mind, it is always advisable to design a building with a roof
overhang so that, in the event of overflow, the water will not flow down the facade or make its
way into the wall, where damage may result. Common materials for gutters and downpipes are
galvanized steel, aluminium and vinyl. Galvanized steel is the least expensive. Aluminium is
long-lasting but easily damaged. Vinyl is both durable and resistant to impact damage.
Two major types of gutter bracket are normally available. One is for fixing the gutter to a fascia,
as illustrated in Figure 8.67. The other is used when there is no fascia board and the gutter is
fixed to the rafters. The roof cover should extend 50 mm beyond the ends of the rafters or the
fascia board in order to let the water fall clear.

Parapet
Parapets are short walls extended above the roof slab. Parapets are installed for flat roofs. It
acts as a safety wall for people using the roof.

Doors
Doors are essential in buildings to provide security and protection from the elements, while
allowing easy and convenient entry and exit. Farm buildings may be served adequately with
unframed board doors, while homes will need more attractive, well-framed designs that close
tightly enough to keep out dust and rain and allow only minimal air leakage. Large openings
are often better served by rolling doors, rather than the side-hinged type.
General characteristics of doors
 Size: Doors must be of adequate size. For use by people only, a door 70 cm wide
and 200 cm high is adequate. However, if a person will be carrying loads with
both hands, e.g. two buckets, between 100 cm and 150 cm of width will be
required. If head loads will be carried, door heights may need to be increased to
250 cm. Shop or barn doors need to be considerably larger to give access for
tools and machinery.
 Strength and stability: Doors must be built of material heavy enough to
withstand normal use and to be secure against intruders. They should be
constructed of large panels, such as plywood, or designed with sturdy, well-
secured braces to keep the door square, thereby allowing it to swing freely and
close tightly. A heavy, well-braced door mounted on heavy hinges fastened with
‘blind’ screws and fitted with a secure lock will make it difficult for anyone to
break in.
 Door swing: Edge-hung doors can be hung at the left or at the right, and operate
inwards or outwards. Careful consideration should be given to which edge of
the door is hinged to provide the best control and the least inconvenience. An
external door that swings out is easier to secure, wastes no space within the
building, and egress is easier in an emergency. However, unless it is protected
by a roof overhang or a verandah, it may be damaged by rain and sun. An
inward-swinging door is better protected from the weather.
 Weather resistance and durability: It is desirable to use materials that are not
easily damaged by weathering, and to further improve the life of the door by
keeping it well painted.
 Special considerations: Under some circumstances, fireproof doors may be
desirable or even mandatory. In cooler climates, insulated doors and weather-
stripping around the doors will help to conserve energy.
Types of door
 Unframed doors: Very simple doors can be made from a number of vertical
boards held securely by horizontal rails and a diagonal brace installed in
such a position that it is in compression. These are inexpensive doors and
entirely satisfactory for many stores and animal buildings. As the edge of
the door is rather thin, strap or tee hinges are usually installed over the face
of the rails.
 Framed doors: A more rigid and attractive assembly includes a frame around
the outer edge of the door held together at the corners with mortise and tenon
joints. The framed door can be further improved by rabbeting the edge of
the frame rails and setting the panels 10 mm to 20 mm into the grooves. The
door can be hung on strap or tee hinges but, as there is an outer frame, the
door can also be hung on butt hinges with hidden screws. If the inner panel
is made of several boards, braces are needed, but, if only one or two panels
are made of plywood, no braces will be required. Large barn or garage doors
will need bracing regardless of the construction of the centre panels.
 Flush Doors: Flush-panel doors consist of a skeleton frame clad with a sheet
facing, such as plywood. No bracing is necessary and the plain surface is
easy to finish and keep clean. Flush-panel doors are easily insulated during
construction if necessary.
 Double Doors: Large door openings are often better served by double doors.
If hinged doors are used, smaller double doors are not as likely to sag and
bend and they are much less likely to be affected by wind. Usually opening
only one of the double doors will allow a person to pass through. Figure
8.70 shows how the meeting point of the two doors can be covered and
sealed with a cover fillet. When doors are large and heavy and need to be
opened only occasionally, it is desirable to place a small door either within,
or next to, the large door. Figure 8.71 shows typical locations for a small
door for the passage of people.
 Rolling Doors: An alternative to double-hinged doors for large openings is
one or more rolling doors. They often operate more easily, are not as
affected by windy conditions and are not as subject to sagging and warping
as swinging doors. Rolling doors are usually mounted under the eave
overhang and are protected from the weather when either open or closed. It
is true that they require space at the side of the doorway when they are open,
but there are several designs to suit a variety of situations.
  Half-door or Dutch door: Doors that are divided in half horizontally allow
the top section to be opened separately to let in air and light while at the
same time restricting the movement of animals and people.

Door frames
A timber door frame consists of two side posts or jambs, a sill or threshold, and a head or
soffit. For simple buildings not requiring tight-fitting doors, the two jambs shown in Figure
8.73 may be all that is required. However, if a tightly fitting door is needed, a complete frame
is required, including strips or stops around the sides and top against which the door closes.

Windows
Windows provide light and ventilation in a building and allow the people inside to view the
surrounding landscape and observe the activities in the farmyard. In sitting rooms and work
rooms where good light and ventilation are important, the window area should be 5–10 percent
of the floor area of the room. Windows sometimes need to be shaded to reduce heat radiation,
or closed to keep out driving rain or dust. In addition, screening may be needed for protection
from insects. Shutters, either top- or sidehinged, are commonly used to provide the required
protection. Side-hung glazed windows, fly screens and glass or timber louvres are also used.
Shutters: These are basically small doors and are constructed as unframed, framed or flush
shutters. Owing to the smaller size, only two rails are required and the timber can be of smaller
dimensions. The principles of construction are the same as for doors.
However, when the frame for the shutter is recessed in the wall, the sill must be sloped and
extend out from the wall to let the water drip clear of the face of the building. The window
shutter can be side-hinged or top-hinged. A top-hinged shutter has the advantage of shading
the opening when kept open, as well as allowing ventilation while preventing rain from
entering.
Glazed windows: Glazed windows are relatively expensive but are most practical in cold areas.
When temperatures are low, the window can be shut while still allowing daylight to enter the
room. Frames for glazed windows are available in wood and metal, metal being more
expensive. Glazed windows with frames are usually marketed as a unit, but Figure 8.79
illustrates various methods of frame construction and installation.

FINISHES
Finishes form an interface between building users and the building hence affect the way in
which we interact and perceive our built environment. Color or the lack of it, affects our
psychology and the atmosphere of our buildings. Materials give of scent and this too will
influence our internal environment and may affect our health, (Stephen et al, 2013).
There are a wide range of finishes i.e. floor, wall, ceiling, painting and decorative.
Types of finish
There are two different types of finish to the building fabric: those inherent in the material and
those applied to the background.
Inherent finishes
Many materials such as timber, stone, brick and glass provide a natural finish without any need
for further work- an inherent finish. Attention to joints, fixings and the quality of work is
critical. When brick and block work is to be left fair face (not plastered) it is important to
specify this so that the joints are built to an appropriate quality. Carefully chosen, materials
with inherent finish may help to reduce construction time and initial construction costs. In
addition, the use of materials with inherent finish maybe an important consideration when
disassembling building and reclaiming materials at a future date for reuse, since the materials
has not been compromised by application of a finish.
Applied finishes: ecological consideration
Applications of materials to the existing backgrounds such as plaster to a wall or paint to
timber, is an applied finish. The durability of the finish will depend upon the material properties
of the finish and the materials it is applied to, as well as the bond between the two materials.
Ecological design goals aim to minimize the pollution from applied finishes. Petrochemical
paints, stains, and varnishes should be avoided and preference given to products with natural
pigments that are not harmful to plants, animals and people.
FUNCTIONAL REQUIREMENTS
The primary function of a surface finish is to provide a durable, visually attractive and low
maintenance surface to floors, walls and ceilings.
External Finishes
External finishes are important in determining the aesthetic appeal of the building. The
external finishes will also, in conjunction with the detailing and quality of the construction,
determining how the building will weather over time. Thus, the quality of materials used for
external finishes and the manner in which they are applied will determine the durability of the
building fabric.

The function requirements are:

 Aesthetic appeal
 Durability
 Strong mechanical and chemical bond to structural substrate
 Flexibility, the ability to withstand thermal and moisture movement (via control joints)
 Health and safety consideration
Internal finishes
Internal finishes are important in creating a sense of place and in helping to ensure a healthy
indoor environment. As we spend a great deal of time within buildings, the quality of internal
environment is particularly important in ensuring a sense of well-being and enjoyment.
Materials will be touched, experienced visually and will give off scent, which combine with
furnishings and appliances will influence our perception of space in which we live or work and
affect indoor air quality.
Functional requirements are:
 Aesthetics
 Durability and flexible ability to withstand thermal and moisture movement
 Ease of maintenance and cleaning
 Strong mechanical or chemical bond to structural substrate.
 Expel water from the surface that forms as condensation (particularly in kitchens and
bathrooms)
 Prevent and resist mould growth or insect attack
 Provide visual finish, high level of contrast (e.g. nosing on stairs).
 Tactile or touch sensitive finish as an aid to those with visual difficulties.
 Non-toxic

FLOOR FINISHES

A floor finish should be level, reasonably resistant to wear, be capable of being maintained
and remain in a safe condition during its designated design life, and capable of being easily
cleaned.
For specific areas of buildings additional requirements such as non-slip, smooth for cleaning
and polishing, resistant to liquid and chemical spillages, seamless for hygiene etc. For small
floor areas the choice of finish is dictated largely by appearance and ease for cleaning
whereas in larger office floor areas, public and institutional buildings, ease of cleaning is a
prime consideration where power operated cleaning and polishing equipment is used.
Finishes to concrete floors
It includes:
 Jointless
 Flexible thin sheet and tiles
 Rigid tiles and stones slabs
 Wood and wood based.
JOINTLESS FLOOR FINISHES
This group includes the cement and resin-based screeds and mastic asphalt. They are laid while
plastic and other than provisions of movement joints they provide a homogeneous surface.
Cement Screeds
A cement and sand-screed finish to a concrete floor may be an acceptable, low-cost finish to a
small area floors of garages, stores and outhouses where the small area does not justify the use
of a power float and considerations of ease of cleaning are not of prime importance. Premixed,
cement and sand screed material reinforced with polymer fibre is available; the fibre reinforces
against drying, shrinkage and cracking. To produce improved surface resistance to wear and
resistance to penetration of oils and grease, a dry powder of titanium alloy with cements may
be sprinkled on the wet surface of concrete or screed and troweled in.
Granolithic Paving
Granolithic paving consists of a mixture of crushed granite, which has been carefully sieved so
that the particles are graded from coarse to very fine in such proportions that the material, when
mixed, will be particularly free of voids of small spaces and when mixed with cement will be
a dense mass. The mixed proportions are normally 21/2 of granite chippings to 1 cement by
volume. These materials are mixed with water and the wet mix is spread uniformly and
troweled to a smooth flat surface. When this paving has dried and hardened it is hard wearing.
There are number of additives variously described as ‘sealer’ or ‘hardeners’, that they may be
added to a granolithic mix to produce improved resistance to surface wear. This floor finish is
used for factories, stores, garages and other large floor areas that have to withstand heavy wear.
Anhydrite floor finish
Premixed, dry bagged screed material of anhydrite and sand is used as a floor finish. Anhydrite
is a mineral product of heating gypsum that will, when mixed with water, act as a cement to
bind the grains into a solid mass as the material dries and hardens. The advantage of anhydrite
is that it is readily combines with water and does not shrink and crack as it dries out and
hardens. The wet mix of anhydrite and sand maybe pumped and spread over the concrete base
as a self-levelling screed or spread and troweled by hand. The material may be pigmented. A
disadvantaged of the material is that it is fairly readily absorbs water and is not suitable to use
in damp situations.
Resin-based floor finish
A range of resin emulsion finishes is available for use where durability, chemical resistance
and hygiene are required in laboratories, hospitals and food preparation buildings. This is
specialist application finish is composed of epoxy resins as binders with cement, quartz,
aggregates and pigments. The material is spread on power floated or cement-screed base by
pumping and troweling to a thickness of up to 12mm. The aggregate maybe exposed on the
surface as a non-slip finish and as a decoration. On larger floor surface areas, it is used for the
advantage of a seamless finish that can be cleaned by a range of power operated devices.
Polymer resin floor surface sealers.
Polyester, epoxy or polyurethane resin floor finish sealers are specialist thin floor finishes used
for their resistance in water, acids, oils, alkalis and some solvents. The materials are spread and
levelled on a level power floated or screed surface to provide a seamless finish which is easy
to clean. Polyester resins, the most expensive of the finishes, is spread to a finish thickness of
2-3mm to provide the greatest resistance. Epoxy resins provides a less exacting resistance. It
is sprayed or pumped to a self-leveling or troweled thickness of 2-6mm. Polyurethane resin,
which has moderate resistance, can be spread on a some-what uneven base by virtue of its
possible thickness. It is pumped to a self-levelling for thin applications and troweled for thicker
applications. Thickness of between 2 and 10mm are used.
Mastic Asphalt Floor finish.
Mastic asphalt serves both as a floor finish and a damp-proof membrane (dpm). It is a smooth,
hard wearing, dust free finish, easy to clean but liable to be slippery when wet and less used
since the advent of thin plastic tiles and sheets.
Flexible thin sheet and tile
Linoleum is made from oxidized linseed oil, rosin, cork or wood floor, fillers and pigments
compressed on a jute canvass backing. The sheets are made in 2m widths, 9-27m lengths and
thickness of 2.0, 2.5, 3.2 and 4.5mm in a variety of colors. The usual thickness of sheet is
2.5mm.
Tiles 300 and 500mm square are 3.2 and 4.5mm thick. Linoleum should be laid on a firm level
base of plywood or particleboard on timber floors or on hardboard over timber boarded floors
and on troweled screed on concrete floors. The material is laid flat for 48 hours at room
temperature and then laid on adhesive and rolled flat with butt joints between sheets. Linoleum
has a semi-matt finish, is quiet and warm underfoot and has moderate resistance to wear for
the usual 2.5mmthick sheets and good resistance to wear for the thicker sheets and tiles.
Linoleum has been used instead of vinyl for the advantage of the strong colours available in
the form of sheets and also in the form of decorative patterns by combining a variety of colours
in various designs from cut sheet material, a characteristic that has seen the material experience
a return to fashion more recently.
Flexible vinyl sheet and tiles
Polyvinylchloride (PVC), generally referred to as vinyl, is a thermoplastic used in the
manufacture of flexible sheets and tiles as a floor finish. The material combines PVC as a
binder with fillers, pigments and plasticisers to control flexibility. The resistance to wear and
flexibility vary with the vinyl content, the greater the vinyl content the better the wear and the
poorer the flexibility.
Vinyl sheet flooring has become the principal sheet flooring used where consideration of cost
and ease of cleaning combine with moderate resistance to wear. Sheet thicknesses from 1.5 to
4.5mm in widths from 1200 to 2100mm are produced in lengths of up to 27 m. Foam backed
vinyl sheet is produced to provide a resilient surface with the advantages of resilience and being
quiet underfoot but at the expense of the material being fairly easily punctured. The material is
extensively used in domestic kitchens and bathrooms and offices where a low cost, easily
cleaned surface is suited to moderate wear.
The thin sheet material should be laid on a smooth, level screeded surface particularly free from
protruding hard grains that might otherwise cause undue wear. The thicker, less flexible sheet
may be laid on a power floated concrete finish. The sheets are bonded on a thin bed of epoxy
resin adhesive and rolled to ensure uniformity of adhesion. For large areas of flooring the sheets
may be heat welded to provide a seamless finish. A range of flexible vinyl tiles is produced in
a variety of colours and textures in 225, 250 or 300mm squares by 1.5 to 3mm thicknesses.
Various shapes of cut sheet may be used to provide single or multi-coloured designs.
Clay floor tiles
Natural clay floor tiles have been used for centuries as a hard, durable floor surface and finish
for both domestic and agricultural ground floors. The two types of tile may be distinguished as
floor quarries and clay floor tiles. The word quarry is derived from the French carr, meaning
square.
Floor quarries
They are manufactured from natural clays. The clay is ground and mixed with water and then
moulded in hand operated presses. The moulded clay tile is then burned in a kiln.
Manufacturers grade tiles according to their hardness, shape and colour. The first or best quality
of these clay floor quarries is so hard and dense that they will suffer the hardest wear without
noticeably wearing. Because they are made from plastic clay, which readily absorbs moisture,
quarries shrink appreciably when burned, and there may be a noticeable difference in the size
of individual tiles in any batch. The usual colours are red, black, buff and heather brown. Some
common sizes are 100 × 100 × 12.5mm thick, 150 × 150 × 12.5mm thick and 229 × 229 ×
32mm thick.
Clay-floor tiles
Where finely ground clay is used, the finished tiles are very uniform in quality and because
little water is used in moulding, very little shrinkage occurs during burning. The finished tiles
are uniform in shape and size and have smooth faces. The tiles are manufactured in red, buff,
black, chocolate and fawn. Because of their uniformity of shape, these tiles provide a level
surface that is resistant to all but heavy wear, does not dust through abrasion, is easily cleaned
with water and has smooth, non-gloss finish which is reasonably non-slip when dry. They are
used for kitchens, bathrooms and halls where durability and ease of cleaning are an
advantage. Some common sizes are 300 x300 x15mm thick, 150 x150 x 12mm thick, and 100
x 100 x 9mm thick.
Vitreous floor tiles
Vitreous tiles are made from clay and felspar, which gives the tile a semi-gloss finish. The tiles
are uniform in shape and size and have very smooth semi-gloss or gloss surface that does not
absorb water or other liquids and can be easily cleaned by mopping with water. Both vitreous
and fully vitreous tiles may be moulded with a textured finish to provide moderately non-slip
surface. The gloss finish is impervious to most liquids, dust-free and liable to be slippery,
particularly when wet. Sizes are generally similar to those of plain colour tiles.

Laying of clay-floor tiles

The considerations that affect the choice of a method of laying floor tiles are:
 Tolerance: the fixing adhesive and tiles must be capable of accommodating any
undulations and variation in the structure to which they are fixed so that the final tile is
level.
 Good adhesion to the base to provide solid support; this is particularly important for
thin tiles if cracking of the tile is to be avoided.
 Providing a means of accommodating relative structural, moisture and thermal
movement between the base and the finish to prevent arching of the tile floor
Tiles are laid by the direct bedding method or thin bed adhesive model.
Direct bedding method
This is traditional method of laying tiles. A layer of wet cement and sand spread over a
screeded or level concrete floor with control joints at the manufacturer’s recommended
spacing.
The direct bedding method of laying is used for plain clay tiles on a bed some 10mm thick and
with joints between 5 and 10mm wide, depending on variations in the size of the tiles and the
need to adjust tile width to that of a whole number of tiles with joints to suit a particular floor
size, thus avoiding the need to cut tiles on site.
Thin bed adhesive method
The majority of the thin, vitreous tiles that are used today are bedded and laid on an adhesive
that is principally used as a bond between the tiles and the base, and to a lesser extent as a bed
to allow for small variations in tile thickness. The adhesives that are used are rubber latex
cement, bitumen emulsion and sand and epoxy resins. These adhesives are spread on a level
power floated concrete or a screed finish, to a thickness of from 3 to 5mm, combed to assist
bedding and the tiles are then pressed and levelled in position. Where the thin bed, epoxy resins
are used as an adhesive for thin, vitreous tiles there should be no large protruding particles of
aggregate or sand in the floor surface over which the brittle tile could crack under load.
Tiles arching-control joints
The word arching is the effect of tiles rising above their bed (the structural floor) in the form
of a shallow arch. Arching is caused by expansion of the tiles relative to their bed or contraction
of the bed relative to the tiles. With most finishing materials it is advisable to provide control
joints, which allow the materials to shrink without causing unsightly cracks and expand without
separating from their substrata.
Concrete tiles
Concrete tiles made of cement and sand, which is hydraulically pressed to shape as floor tiling,
have been used as a substitute for quarry and plain colour clay tiles. The usual size of tiles is
300 × 300 × 25mm, 225 × 225 × 19mm and 150 × 150 × 16mm. The material may be
pigmented or finished to expose aggregate. The density and resistance to wear depend on
quality control during
manufacture and the nature of the materials used. They are laid on a level power floated
concrete or screed surface and jointed in the same way as quarries and plain colours.
Stones slabs
A wide range of natural stone slabs is used as a floor finish, from the very hard slabs of granite
to the less dense soft marbles. Stone is selected principally for the decorative colour, variations
in colour, grain and polished finish that is possible, and for durability. The method of bedding
natural stone slabs as an internal floor finish varies with the thickness, size, nature and
anticipated wear on the surface. Large, thick slabs of limestone, sandstone and slate up to 50mm
thick are laid on cement and sand with cement and sand joints. Thin slabs of granite and marble
are laid by the thin bed adhesive method or the dry sand bed method, which is usually used for
marble.
Joints
The width of the joints between tiles and slabs as an internal floor finish is determined by the
uniformity of shape of the material used. For quarries, joints of up to 12mm may be necessary
to allow for the variations in size, and joints as little as 1mm may be possible with very
accurately cut and finished thin slabs of granite and marble. The disadvantage of wide joints is
that the material used, such as cement and sand for quarries, will be more difficult to clean and
will more readily stain than the floor material. Ideally, the jointing material should have
roughly the same density, resistance to wear and ease of cleaning as the floor finish.
Control joints
The joints between tiles and slabs will serve the purpose of accommodating some movement
of the floor finish. Some small expansion or contraction of the floor finish will be taken up in
the joints through slight cracks or crushing of the very many joints.
Timber floor finishes
Natural wood floor finishes such as boards, strips and blocks are used for the advantage of the
variety of colour, grain and texture of this natural material, which is warm, resilient, and
comparatively quiet underfoot.
Floorboards
Floorboards may be used as a floor surface to timber and to concrete floors. Either plain edge
or tongued and grooved boards are used. The boards are nailed to wood battens set in a screed
or to battens secured in floor clips. More usually, wood strip flooring is used.
Wood strip flooring
Strips of hardwood or softwood of good quality, specially selected so as to be particularly free
of knots, are prepared in widths of 90mm or less and 19, 21 or 28mm in thickness. The type of
wood chosen is one that is thought to have an attractive natural colour and decorative grain.
The edges of the strip are cut so that one edge is grooved and the other edge tongued, so that
when they are put together the tongue on one fits tightly into the groove in its neighbor. The
main purpose of the tongue and groove (T & G) is to interlock the strips so that its neighbours
resist any twisting within an individual strip of timber.
Wood block floor finish
Blocks of wood are used as a floor finish where resistance to heavy wear is required, as in halls,
corridors and schools, to provide a surface which is moderately resilient, warm and quiet
underfoot. An advantage of the comparatively thick blocks is that after wear the top surface
may be sanded to reduce the block to a level surface. The blocks are usually 229 to 305mm
long by 75mm wide by from 21 to 40mm thick and are laid on the floor in a bonded,
herringbone or basket weave pattern.
WALL AND CEILING FINISHES
Fairface finishes
Fairface brickwork, blockwork.
Fairface brickwork or blockwork is used to describe the higher standard of finish (workmanship
and quality of bricks or blocks) that is required to provide an aesthetically pleasing appearance.
Particular attention is given to the joints; the perpendicular joints should line up vertically and
all of the mortar joints should be of a consistent thickness. A neat joint should be formed and
drips and snots of mortar should not be allowed to come into contact with the face of the
brickwork. A wide variety of rough, smooth and polished facing blocks and bricks are
available. The type of brick or block selected will depend on the performance requirements,
for example the performance requirements of fairface blockwork in industrial buildings, sports
halls, showrooms, and large arenas (which may accommodate concerts) are quite different.
Internal plastering and dry lining
Plaster is the word used to describe the material that is spread (plastered) over irregular wall
and ceiling surfaces to provide a smooth and level finish. The initially wet material is spread
and levelled over uneven backgrounds such as brickwork, and over lath fixed to the underside
of timber floor joists so that as it hardens and dries it forms a smooth, level wall and ceiling
finish. The purpose of plaster is to provide a smooth, hard, level finish, which can be painted
with emulsion paint, or to which wallpaper can be applied.
Airtightness and wet plaster and dry lining methods
Brick and block walls on their own are not particularly airtight. Gaps between horizontal joints,
weep holes and unsealed cavities provide an interconnected passage of air from the inside to
the outside of the dwelling. Wet plaster methods have been found to greatly improve the
airtightness of masonry walls. Dry lining does not have the same effect. To increase airtightness
when using plasterboard, it is suggested that a ribbon of plaster (continuous strip of plaster)
should be placed around the perimeter of each board. Another method to increase airtightness
is to coat the surface of the blockwork with a thin layer of rough plaster (2–3 mm) prior to
applying the plasterboard.
Plaster undercoats and finish coat
The finished surface of plaster should be flat and fine textured (smooth). It would seem logical,
therefore, to spread some fine grained material, such as lime or gypsum mixed with water, over
the surface and trowel it smooth and level. The maximum thickness to which a wet, fine-
grained material can be spread and levelled is about 3mm. The irregularities in the surface of
even the most accurately laid brick or blockwork are often more than 3mm and it would be
necessary to apply two coats to achieve a satisfactory finish.
Materials used in plaster
Lime plaster: - Lime plaster is used in the restoration and preservation of older buildings.
Lime is mixed with sand and water in the proportion of 1 of lime to 3 parts of sand by volume,
with water for use as undercoat, and by itself mixed with water as a finish coat.
Cement plaster: - Cement is mixed with sand and water for use as an undercoat for application
to brick and block walls and partitions. It is used on strong backgrounds as 1 part of cement to
3 or 4 parts of clean, washed sand by volume. A wet mix of cement and clean sand (sharp sand)
is not plastic and requires a deal of labour to spread. It is usual, therefore, to add a plasticiser
to the wet mix to produce a material that is at once plastic and sets and hardens to form a hard
surface.
Gypsum plaster: - The advantage of gypsum plasters is that they expand very slightly on
setting and drying and are not, therefore, likely to cause cracking of surfaces. Gypsum is a
chalk-like mineral, being a crystalline combination of calcium sulphate and water
(CaSO42H2O). It is available as both natural gypsum, which is mined in areas all over the
world, and as a synthetic by-product of major industries such as fossil fuelled power stations.
Casting plaster: - Finely ground hemihydrate gypsum (plaster of Paris) when mixed with
water sets and hardens so quickly (about 10 minutes) that it is unsuitable for use as a wall or
ceiling plaster. It is ideal for making plaster casts for buildings. Wet plaster of Paris is brushed
into moulds to provide cornices and other decorative plasterwork.
Retarded hemihydrate gypsum plaster: - The gypsum used for undercoats is retarded
hemihydrate gypsum in which a retarding agent is added to plaster of Paris to delay the setting
time for 1.5 to 2 hours to allow time for spreading and levelling the wet material as undercoat.
Pre-mix gypsum undercoat: - The advantage of this material is that the pre-mix avoids the
messy, wasteful operation of mixing dry powdered lime or cement with sand. The wet mix is
comparatively easy to spread and level and the lightweight aggregate gives a small degree of
thermal insulation.
Bonding undercoat: - Where the undercoat plaster is to be applied to a surface with
particularly low suction, which does not readily absorb water, gypsum bonding undercoat is
formulated to provide adequate adhesion.
High impact undercoat: - In some situations where it is anticipated that rough or careless
usage may damage standard undercoat plaster, high impact gypsum undercoat is used.
Finish plaster: - Finish plaster is powdered, retarded hemihydrate gypsum by itself for use as
a thin finish coat for both gypsum undercoats and to plasterboards. Mixed with water the plaster
is spread and finished to a thickness of about 2 to 5mm and sets in about 1 to 2 hours.
Anhydrous gypsum plaster: - Anhydrous gypsum plaster was commonly used as a thin finish
coat to cement based undercoats. The powdered gypsum is mixed with a mineral sulphate to
accelerate its set, which otherwise would be so slow as to make it unsuitable for use as a finish
plaster.
One coat gypsum plaster: - One coat plasters are retarded hemihydrate plasters, which
combine the properties of an undercoat and a finish coat. One coat is applied to a thickness of
up to 20mm as an undercoat. As the plaster begins to set (stiffen) it is sponged with water and
trowelled to bring the fine particles to the surface so that it may have a finish comparable to
that of a separate finish coat.
Machine applied gypsum plaster: - Machine applied, or projection, plasters are one coat
gypsum plasters designed to provide a longer setting time to allow for mixing, pumping,
spreading and trowelling. The material is mixed with water, pumped and applied to the wall by
a projection machine, which effectively halves the application time it would take to spread by
hand.
BACKGROUND SURFACES FOR PLASTER
The surface of walls to be plastered will affect the type of plaster used and its application. The
surface of rough textured bricks and concrete blocks affords a ‘key’ for the mechanical
adhesion of plaster to the background wall. As the wet plaster undercoat is spread and pressed
into the surface, wet plaster fills the irregularities and as it hardens it forms a mechanical key
to the background.
Suction
The word suction is used to describe the degree to which a surface will absorb water and so
assist in the adhesion of plaster to a surface. Some lightweight concrete blocks readily absorb
water and have high suction to the extent that wet plaster applied to them may lose so much
water that it is difficult to spread and may not fully set due to loss of water. Suction may be
reduced by spraying the surface with water prior to plastering or by the use of a liquid primer.
PVA bonding agent
There are two main types of treatment to improve the adhesion of plaster to surfaces with low
suction, such as concrete, to avoid the laborious process of hacking the surface to provide a
key. The first is based on polyvinyl acetate (PVA) that is brushed or sprayed on to the surface.
The plaster is applied before the PVA has fully dried and is still tacky; it is the tackiness that
provides the bond.
Polymer bonding agent
The second pre-treatment is polymer based and incorporates silica sand. Once the polymer is
fully dry the plaster is applied and gains bond through the silica grains and does not, therefore,
depend on applying plaster as soon as the bonding agent is tacky.
Reinforcement for angles
A range of galvanised steel beads and stops is made for use with plaster and plasterboard as
reinforcement to angles and stops at the junction of wall and ceiling plaster and plaster to other
materials. An angle bead is pressed from steel strip to form reinforcement to angles.
PLASTER FINISHES TO TIMBER JOISTS AND STUDS
Timber lath
The original method of preparing timber ceilings and timber stud walls and partitions for plaster
was to cover them with fir lath spaced about 7 to 10mm apart to provide a key for the plaster.
The usual size of each lath is 25mm wide by 5 to 7mmthick, in lengths of 900mm. The softwood
lath is either split or sawn from fir. Seasoned fir lath is nailed across the joists or timber studs.
Obviously, the ends of the laths must be fixed to a joist or stud and the butt end joints of laths
staggered to minimize the possibility of cracks in the plaster along the joints.
Metal lath (EML)
This lath is made by cutting thin sheets of steel so that they can be stretched into a diamond
mesh of steel, as shown in Figure 10.8. This lath is described as EML (expanded metal lath).
The thickness of the steel sheet, which is cut and expanded for plasterwork, is usually 0.675mm
and the lath is described by its shortway mesh. A mesh of 6mm shortway is generally used for
plaster. To prevent expanded steel lath rusting it is either coated with paint or galvanised. As a
background for plaster on timber joists and studs, the lath, which is supplied in sheets of 2438
× 686mm, is fixed by nailing with galvanised clout nails or galvanised staples at intervals of
about 100mm along each joist orstud. During fixing, the sheet of lath should be stretched tightly
across the joists. Edges of adjacent sheets of the lath should be lapped by at least 25mm.
Gypsum plasterboard
Gypsum plasterboard consists of a core of set (hard) gypsum plaster enclosed in, and bonded
to, two sheets of heavy paper. The heavy paper protects and reinforces the gypsum plaster core,
which otherwise would be too brittle to handle and fix without damage. Plasterboard is made
in thickness of 9.5mm, 12.5mm, 15mm and 19mm, for use either as a dry lining or as a
background for plaster in boards of various sizes. Plasterboard is extensively used as a lining
on the soffit (ceiling) of timber floors and roofs and on timber stud partitions.
Gypsum wallboard
Gypsum wallboard, which is the most commonly used board, is principally made for use as a
dry lining wallboard to timber or metal stud frames with the joints between the boards filled
ready for direct decoration. The boards have one ivory colored surface for direct decoration
and one grey face. The boards are 9.5, 12.5 and 15mm thick, from 900mm wide and up to
3600mm long.
Gypsum baseboard
Gypsum base board is designed specifically for use as a base for gypsum plaster. The board is
9.5mmthick, 900mmwide and 1220mmlong, and used as ceiling lining for their manageable
size. The boards have square edges. The boards are fixed with 30mmnails at 150mmcentres
with a gap of about 3mmat joints. The joints are filled with filler into which reinforcing paper
tape is pressed and the boards are covered with board finish gypsum plaster that is spread and
trowelled smooth to a thickness of 2 to 5mm.

Gypsum plank
Gypsum plank is 19mm thick, 600mm wide and 2350 and 3000mm long with either tapered
edges for seamless jointing for direct decoration or square edges for plastering. This thicker
board, which may be used for enhanced fire resistance or a small increase in sound insulation,
may be fixed at 600mm centres with 60mmnails.
Gypsum lath
These comparatively small boards are made specifically as a base for ceiling lining for ease of
holding and fixing and as a base for plaster either as a thin skim coat or more particularly for a
two-coat finish. The two-coat finish is preferred, as the undercoat will facilitate accurate
levelling over the many joints. Lath is 400mm wide, 1200mm long and 9.5 and 12.5mm thick.
The long edges of the boards are rounded. The lath is fixed to timber joists and ceiling with a
gap of not more than 3mmbetween boards. The lath is covered and finished with one finish
coat to a thickness of up to 5mm or more, usually with a gypsum undercoat 8mm thick and a
finish coat of about 2mm thickness.
SKIRTINGS AND ARCHITRAVES
Skirting
A skirting (or skirting board) is a narrow band of material formed around the base (skirt) of
walls at the intersection of wall and floor. Usually the skirting sits proud of the wall surface. It
serves to emphasize the junction of vertical and horizontal surfaces, wall and floor, and is made
from material that is sufficiently hard to withstand knocks. The skirting protects the wall finish
at a vulnerable point and also covers the joint between wall and floor. The materials commonly
used for skirting are timber, mdf, plastic, metal and tile.
Timber skirting board
Softwood boards, 19 or 25mm thick, from 50 to 150mm wide and rounded or moulded on one
edge are usually used. The skirting boards are nailed to plugs, grounds or concrete fixing blocks
at the base of walls after plastering is completed.
MDF
Medium Density Fibre board is increasingly used as a timber-based material into which
grooves, rebates and complicated shapes can be cut. The material, which is made from fine
particles of wood compressed and glued together, is less expensive than other timber boards,
easy to work and finish and is more flexible than most naturalwoodboards. Where timber
finishes are to be painted rather than varnished, mdf may offer an acceptable alternative to
wood-based products in their more natural form.
Metal skirting
The traditional wood skirting was initially used to mask the joint between wall plaster and
timber floor finishes where it was impossible to make a neat joint between lime plaster and
boarded floors. The plasters used today are less liable to shrinkage and cracking and may be
finished directly on to solid floor finishes or down on to pressed metal skirtings. A range of
pressed steel skirtings is manufactured for fixing either before or after plastering. The skirting
is pressed from mild steel strip and is supplied painted with one coat of red oxide priming paint.
Tile skirting
The manufacturers of most floor tiles also make skirting to match the colour and size of their
products. The skirting tiles have rounded top edges and a cove base to provide an easily cleaned
rounded internal angle between skirting and floor. The skirting tiles are first thoroughly soaked
in water and then bedded in sand and cement against walls and partitions as the floor finish is
laid.
Architrave
The word architrave describes a decorative moulding fixed or cut around doors and windows
to emphasise and decorate the opening. An architrave can be cut or moulded on blocks of stone,
concrete or clay, built around openings externally. Internal architraves usually consist of
lengths of moulded wood nailed around doors and windows. An internal wood architrave
serves two purposes: to emphasise the opening and to mask the junction of wall plaster and
timber door or window frame.

EXTERNAL RENDERING
Owing to their colour and texture, common bricks, concrete and clay blocks do not provide
what is commonly considered to be an attractive external finish for buildings. The external
faces of walls built with these materials are often rendered with two or three coats of cement
and lime mixed with natural aggregate and finished either smooth or textured.
TYPES OF RENDER
Smooth or wood float finish
Smooth (wood float finish) rendering is usually applied in two coats. The first coat is spread
by trowel and struck off level to a thickness of about 11mm. The surface of the first coat is
scratched before it dries to provide key for the next coat. The first coat should be allowed to
dry out. The next coat is spread by trowel and finished smooth and level to a thickness of about
8mm. The surface of smooth renderings should be finished with a wood float rather than a steel
trowel. A steel trowel brings water and the finer particles of cement and lime to the surface,
which, on drying out, shrink and cause surface cracks. A wood float (trowel) leaves the surface
coarse textured and less liable to surface cracks. Three-coat rendering is used mostly in exposed
positions to provide a thick protective coating to walls. The two undercoats are spread,
scratched for key and allowed to dry out to a thickness of about 10mm for each coat; the third
or finishing coat is spread and finished smooth to a thickness of from 6 to 10mm.
Spatterdash
Smooth, dense wall surfaces such as dense brick and situ-cast concrete afford a poor key and
little suction for renderings. Such surfaces can be prepared for rendering by the application of
a spatterdash of wet cement and sand. A wet mix of cement and clean sand (mix 1:2, by volume)
is thrown on to the surface and left to harden without being trowelled smooth. When dry it
provides a surface suitable for the rendering, which is applied in the normal way.
Scraped-finish rendering
An undercoat and finish coat are spread as for a smooth finish and the finished level surface,
when it has set, is scraped with a steel straight edge or saw blade to remove some 2mm from
the surface to produce a coarse textured finish.
Textured finish
The colour and texture of smooth rendering appear dull and unattractive to some people and
they prefer a broken or textured surface. Textured rendering is usually applied in two coats.
The first coat is spread and allowed to dry as previously described. The second coat is then
spread by trowel and finished level. When this second coat is sufficiently hard, but still wet, its
surface is textured with wood combs, brushes, sacking, wire mesh or old saw blades. A variety
of effects can be obtained by varying the way in which the surface is textured. An advantage
of textured rendering is that the surface scraping removes any scum of water, cement and lime
that may have been brought to the surface by trowelling and which might otherwise have
caused surface cracking.
Pebbledash (drydash) finish
This finish is produced by throwing dry pebbles, shingle or crushed stone on to, and lightly
pressed into, the freshly applied finish coat of rendering, so that the pebbles adhere to the
rendering but are mostly left exposed as a surface of pebbles. Pebbles of from 6 to 13 gauge
are used. The undercoat and finish coat are of a mix suited to the background and are trowelled
and finished level. The advantage of this finish is that the pebbledash masks any hair cracks
that may open due to the drying shrinkage of the rendering.
Roughcast (wetdash) finish
A wet mix of rendering is thrown on to the matured undercoat by hand to a thickness of from
6 to 13mm to produce a rough irregular textured finish. The gauge of the aggregate used in the
wet mix determines the finish.
Machine applied finish
A wet mix of rendering is thrown on to a matured undercoat by machine to produce a regular
coarse textured finish. The texture of the finish is determined by the gauge of the aggregate
used in the final wetdash finish, which may have the natural colour of the materials or be
coloured to produce what are called Tyrolean finishes.
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