ADAMA UNIVERSITY
DEPARTMENT OF CIVIL ENGINEERING
BUILDING CONSTRUCTION
CHAPTER 11
Roofs and Roof Coverings
CONSTRUCTION
• Roof can be defined as the upper most part of the building
• It is provided as a structural covering to protect the building
from external weather exposure such as rain, sun, wind etc
• The structural elements may be trusses, beams, slabs,
shells or domes
o Load bearing walls
They are the structural part of the building
Built on a continuous foundation
Support the entire load including their own
Must have sufficient strength and stability,
durability, fire resistance, weather resistance,
thermal and sound insulation.
o None load bearing walls
They are not the structural part of the building
Support their own weight only
Simply to serve as screen for privacy
Used in a framed structure
Partition walls
A partition wall is a thin internal wall which is
constructed to divide the space within the building
into rooms or areas.
It may either be non-load bearing or load bearing.
A load bearing partition wall is called an internal
wall.
Weather exclusion and thermal insulation do not
arise as criteria in the design of internal walls
Requirements to be fulfilled by partition walls
It should be strong enough to carry its own weight
It should be strong enough to resist impact to
which the occupation the building is likely to
subject them.
It should have the capacity and be strong enough
to support suitable decorative surface and some
wall fixtures like wash basin, sink, etc..
It should be as thin as possible
It should act as a sound barrier spatially when it
divides two rooms.
It should be fire resistant
Types of partition walls
Brick partitions
Clay block partitions
Concrete (cast in-situ or pre-cast concrete)
partitions
Light-weight building board(or slab) partitions eg.
Plaster wall board
Timber partitions
Plywood partitions
Wood-chip board partitions
Separating wall
• It is a wall separating different occupants within
the same building
Cross wall
• Is a particular form of load-bearing wall
construction in which all the loads are carried by
internal walls, running at right angles to the length
of the building.
Cavity walls
• A cavity wall is the one which consists of two
separate walls, with a capacity or lap in between.
• The two leaves of a cavity wall may be of equal
thickness if it is a none-load bearing wall, or the
internal leaf may be thicker for load bearing walls.
• The two portions of the wall may be connected
together by a metal pins(wall pins)
• Are often constructed for better thermal and
sound insulation
Advantages of cavity wall over other walls
• There is no direct contact between the inner and outer
leaves of the wall (except at the wall ties). Hence the
external moisture (dampness) can’t travel inside the
building.
• The cavity between the leaves is full of air which is
bad conductor of heat. Hence the transmission of heat
from external face to the internal face is very much
reduced (about 25% greater insulating value than
solid masonry)
• Cavity walls also offer good insulation against sound.
• Load on foundations are reduced because of leaser
solid thickness.
The functional requirements of a wall depend
upon its form of construction
The popular form of construction are:-
1) Masonry walls
2) Monolithic walls
Masonry walls
Is built of individual blocks of materials such as
stone, bricks, hollow concrete blocks(HCB), etc.
usually in horizontal courses cemented together
with mortar
Monolithic walls
o Built of a material requiring some sort of shuttering
in the initial stages.
o The popular forms of monolithic walls are:-
Traditional earth walls and
Modern reinforced concrete walls
Masonry walls
Masonry can be classified into the following
categories
1) Stone masonry
2) Brick masonry
3) Hollow concrete block masonry
4) Reinforced masonry
5) Composite masonry
Definition of terms
Course:- a course is a horizontal layer of bricks, HCB,
or stones
Bed:- the surface perpendicular to the line of pressure
Back:- the inner surface of a wall which is not
exposed
Face:- the exterior of a wall exposed to weather
Hearting:- the interior portion of a wall between the
facing and backing
Side:- the surface forming the boundary in a direction
transverse to the face and bed
Joint the junction of two or more blocks
Header:- is a block which lies with its greatest length
at right angles to the face of the work
Stretcher :-is a block which lies with its greatest
length parallel to the face of the work
Bond:- the method of arranging blocks so that the
individual units are tied together
Spalls:- these are the chips of stones used for filling the
interstices in stone masonry
Quoins:- these are the stones used for the corners of walls of
a structure
Bat:- the portion of brick cut across the length
Closer:- the portion of brick cut along the length (in such a
manner that its one long face remain uncut)
Queen closer:- it is the portion of a brick obtained by cutting
a brick length-wise in to two portions
King closer:- these are the portions of a brick obtained by
cutting off the triangular peace between the center of one end
and the center of one side.
Bevelled closer:- portion of the brick in which the whole
length of the brick is bevelled for maintaining half width of one
end and full width at the other.
Frog:- It is an indentation or depression on the top of a brick
made with the object of forming a key for a mortar.
Head
Joint
Basic brick work terminologies Bed
Joint
Course - horizontal layer of brick
16
Basic brick work terminologies
Rowlock -
laid on face,
end visible
Stretcher - long dimension
horizontal & face parallel to the wall
Soldier - Laid on its end, face
parallel
It is the art of building the structures with stones
Uses of stone masonry
Building foundations, dams, monumental
structures
Building walls, piers, columns, pillars, light houses,
and architectural works
Arches, domes, lintels, and beams
Roofs, floors, paving jobs
Railway ballast, blackboards, electrical
switchboards, etc.
Selection of materials depends upon:-
Availability
Ease of working
Appearance
Strength and stability
Polishing characteristics
Economy
durability
It is the process in which the stone surfaces
specially the facing are prepared to a form fit to be
used for any construction work.
Dressing is carried out either manually with the
help of hand hammers, chisels, axes or machines.
Uses of dressing of stone
Gives desired shape to stones
Reduces the mortar joint width
Improves the appearance of stone surface
Every stone has to be dressed involving the following
stages
Sizing:- in this process the irregular blocks of the stones
are reduced to desired dimensions by removing extra
portions with the help of common tools like hand hammers
and chisels
Shaping:- It involves removing the sharp projection and
other irregularities from edges, corners and surfaces.
Planing:- In this process stones are cleared off all the
irregularities from the surfaces
Finishing:- it consist of rubbing the surface of the stone
with a suitable abrasive material like silicon carbide in the
presence of water
Polishing:- carried out by grinding the stone with abrasives
either manually or with the help of machines. For stones
capable of yielding extremely pleasing patterns. eg. Marble
and granite
Polished Surface
Rough Texture
Based on the arrangement of the stones in the
construction and the degree of refinement in the
surface finish, the stone masonry can be classified
broadly in the following two categories:-
1) Rubble masonry
2) Ashlar masonry
Rubble masonry
In this category the stones used are either
undressed or roughly dressed having wider joints
Random rubble uncoursed
This is the cheapest, roughest and poorest form of
stone masonry
The stones used in this type of masonry are very
much vary in their shape and size and are directly
obtained from the quarry.
Can be uncoursed random rubble or uncoursed
square rubble
• Bigger stone blocks are employed as quoins and
jambs to increase the strength of masonry
• The vertical joints are not constructed in plumb.
uncoursed square rubble
• The stone blocks are made roughly square with
hammer.
• They can be of varying size and are placed in
irregular pattern.
• Generally the facing stones are given hammer
dressed finish.
• More uniform joint is made in the facing and better
appearance is obtained by arranging stones in
series
• Large size stones are employed as quoins
Coursed random rubble
The method of construction is the same as above
• The course is roughly leveled up-to form courses
varying from 30 to 45 cm thick
• All the courses are of the same height
• Construction of this type of masonry, quoins are
built first and line (string) is stretched between the
tops of quoins
Uncoursed square rubble
Square rubble masonry uses stones having
straight bed and sides
The stones are arranged on face in several
irregular pattern
Coursed square rubble
• This type of masonry is also uses the same stone
as uncoursed square rubble but the work is
levelled up to courses of varying depth
• The courses are of different heights
Regular coursed square rubble
• In this type of masonry the wall, consists of
various courses of varying height, but the height
of stones in one course is the same
Polygonal rubble masonry
• Stones are bedded in position to show face joints
running irregularly in all directions
• The first type the stones are only roughly shaped
resulting in only rough fitting
• In the second type the faces of stones are more
carefully formed so that they fit more closely
Flint rubble masonry
• The stone used in this masonry are flints or
cobbles, which vary in width the thickness from
7.5 to 15cm and length from 15 to 30cm
• The face arrangement of the cobbles may be
either coursed or un coursed
• Strength of flint wall may be increased by
introducing lacing coursed of either thin long
stone or bricks at vertical internal of 1 to 2 meters
Ashlar masonry
Ashlar masonry consists of blocks of accurately
dressed stone with extremely fine bed and end
joints.
Ashlar fine tooled
• The finest type of none masonry work
• Each stone is cut to regular and required size and
shape so as to have all sides rectangular, so that
the stone gives perfectly horizontal and vertical
joints with adjoining stone.
Ashlar rough tooled (bastard ashlar)
The beds and sides of each stone block are finely
chisel dressed just in the same manner as for
ashlars fine but the exposed face is dressed by
rough tooling.
Ashlar rock faced (rustic or quarry faced)
• The exposed face of the stone is not dressed but
is kept as such so as to give rock facing.
• A strip of width about 25mm is provided around
the perimeter of the exposed face of every stone
Ashlar chamfered
This is the special form of rock faced ashlars
masonry in which the strip provided around the
perimeter of the exposed face is chamfered or
beveled at an angle of 45
Around this beveled strip, another strip of 15cm is
dressed with the help of chisel
Ashlar facing masonry
• Is provided along with block or concrete block
masonry , to give better appearance.
• The sides and beds of each block are properly
dressed so as to make them true to shape.
• The exposed face of the stone are rough tooled
and chamfered.
• The backing of the wall maybe made in brick
masonry
Brick masonry
• Brick masonry is made of brick units bonded
together with mortar.
Two essential components of brick masonry are
therefore:
• Bricks
• Mortar
Types of bricks
Bricks used in masonry can be of two types
• Traditional bricks
• Modular bricks
Traditional bricks
Are those which have not been standardized in
size.
The dimensions of traditional bricks vary from
place to place.
Modular bricks
• Any bricks which is of uniform size as laid down
by standards.
Bonds in brick work
• Bond is the interlacement of bricks
Rules for bonding
For getting good bond the following rules should be
observed.
1) The bricks should be of uniform size.
2) The length the brick should be twice the length of the
width plus one joint, so that uniform lap is obtained.
Good bond is not possible if lap is non-uniform.
3) The amount of lap should be minimum ¼ brick along
the length of the wall and ½ brick across the
thickness of the wall.
4) Use of brick bats should be discouraged, except in
special locations.
5) In alternate courses, the centre line of header
should coincide with the centre line of the
stretcher, in the course bellow and above it.
6) The vertical joints in the alternate courses should
be along the same prepend.
7) The stretchers should be used only in the facing;
they should not be used in the hearting. Hearting
should be done in headers only.
Types of bonds
The types of bonds provided in brick work are:
• Stretcher bond
• Header bond
• English bond
• Flemish bond
• Facing bond
• English cross bond
• Brick on edge bond
• Dutch bond
• Raking bond
• Zigzag bond
• Garden wall bond.
Stretcher bond
Is the one in which all the bricks are laid as
stretchers on the faces of the walls.
The length of the bricks are along the direction of
the wall.
Used for the walls having a width of half brick
(12cm).
The bond is not possible if the thickness of the wall
is more.
Header bond
Is the one in which all the bricks are laid as
headers on the faces of the walls.
The width of the wall is along the directions of the
walls.
Used only when the thickness of the wall is equal
to one brick length (25cm).
The overlap is usually kept equal to half brick
length.
Three-quarter bats are used in each alternate
courses as quoins.
The bond doesn’t have strength to transmit
pressure in the direction of the length of the wall.
Unsuitable for load bearing walls.
English bond
This is the most commonly used bond for all wall.
The bond is considered to be the strongest
The bond consists of alternate courses of headers
and stretchers
The vertical joints of the header courses are come
over each other.
Similarly, the vertical joints of the stretcher
courses come over each other.
In order to break the vertical joints in the
successive courses, it is essential to place queen
closer after the first header(quoin header) in each
header courses.
Flemish bond
In this type of bond, each course is comprised of
alternate headers and stretchers.
Have better appearance than English bond
Every alternate courses starts with a header at
the corner.
Queen closers are placed next to quoin header in
alternate courses to develop the face lap.
Every header is centrally supported over the
stretchers bellow it.
Flemish bonds are of two types
Double Flemish bond
Single Flemish bond
Double Flemish bond
• Each course presents the same appearance both in
the face and the back.
Single Flemish bond
• Comprised of double Flemish bond facing and English
bond backing and hearting in each course
• This bond thus have the strength of English bond and
the appearance of Flemish bond.
• Used for wall thickness at least one and half brick.
• Double flemish bond facing is done with good quality
expresive bricks, however cheaper bricks can be used
for backing and hearting.
Comparison of english bond and flemish bond
English bond is stronger than flemish bond for walls
thicker than one and half.
Flemish bond gives more pleasing appearance
than the english bond
Brocken bricks can be used in the form of bats in
flemish bond. However more mortar is required.
Construction in flemish bond requires more skill in
comparison with english bond
Dutch bond
It is a modified form of English bond. In this bond
the corners of the wall are strengthened.
Special featurs of this type of bond is as follows
Alternate courses of headers and stretchers are
provided as in english bond.
Every stretcher course starts at the quoin with a
three quarter bat.
In every alternate stretcher course, a header is
placed next to the three-quarter brick bat provided
at the quoin.
STAGE 1
Consideration to be given to the following :~
1. Building type and usage.
2. Building owner's requirements and preferences.
3. Local planning restrictions.
4. Legal restrictions and requirements.
5. Site restrictions.
6. Capital resources.
7. Future policy in terms of maintenance and
adaptation.
Stage 2
Decide on positions, sizes and shapes of
openings
stage 3
Decide on style, character and materials for
openings
Stage 4
Decide on basic materials for fabric of walls and
roofs
Stage 5
Review all decisions and make changes if
necesary.
Typical Details ~
Bonding ~ an arrangement of bricks in a wall,
column or pier laid
to a set pattern to maintain an adequate lap.
Purposes of Brick Bonding ~
1. Obtain maximum strength whilst distributing the
loads to be
carried throughout the wall, column or pier.
2. Ensure lateral stability and resistance to side
thrusts.
3. Create an acceptable appearance.
Simple
