Download 11729845997116 CEC 105 Theory

UNESCO-NIGERIA TECHNICAL &
VOCATIONAL EDUCATION REVITALISATION
PROJECT-PHASE II
NATIONAL DIPLOMA IN
CIVIL ENGINEERING
TECHNOLOGY
CIVIL ENGINEERING CONSTRUCTION I
COURSE CODE: CEC105
YEAR I- SEMESTER I
THEORY
Version 1: December 2008
TABLE OF CONTENTS
Week 1
Building Component
Week 2
Site Preparation
Week 3
Method of Setting Out
Wee 4
Excavations
Week 5
Foundations
Week 6
Damp Proofing, Sub-Structural Works, Rising and seepage of ground
and underground water
Week 7
Floors
Week 8
Walls
Week 9
Brick Bonding
Week 10
Partition Walling
Week 11
Stairs/Staircase
Week 12
Roofs
Week 13
Flat Roofs
Week 14
Slates
Week 15
Suspended Ceilings System
WEEK 1
COURSE: CIVIL ENGINEERING CONSTRUCTION 1
1.0
BUILDING COMPONENTS
1.1
Explain the term Building Component
To understand and to be able to explain the term building component.
It will be necessary to take cognizance of the following definitions:
BUILD – This is to make by putting elements, parts or materials
together to form something.
CONSTRUCTION – This is the putting together and assembling of
elements and material in other to erect or build a structure.
BUILDING – This is the act of constructing houses.
COMPONENT – This is a word that describes an element, part or
materials that contribute to the formation of a structure.
From the above definitions, it could be stated that Building
Components are structural elements or materials that can be
assembled, by the following approved construction procedures and
rules, to make up or form a building. The components to be used
depend largely on the purpose of the building (i.e. residential, factory
or recreations, etc.). high-rise building. Examples of building
components are foundation floor, wall ceiling, roof, doors, windows,
etc.
A building is so called because of the assemblage of most of these
components. Absence of some of these component parts depending
on the purpose of the building, will render it incomplete, structurally
waste and inhabitable. E.g. imagine a building without a foundation,
walls or roof, will be as good as piece of land with first farmers a tree
without root, man with
1.2
Enumerate the building components, e.g. foundation, floor, wall,
ceiling, roof, fenestration, doors, windows, stairs, etc.
Foundation
Columns
Floor
Slabs
Wall
Ceiling
Roof
Fenestration
Doors
Windows
Stairs
Chimney
1.3
Identify the different functional requirements of building
components
The component parts or materials that make up or forms a building
are normally designed to perform some specific function or for a
specific purpose in the building. Part from the beautification of the
structure, building components should perform some certain
functional requirements as identified below:
1.
Foundation: To safety its objectives, foundation must be
designed to satisfy certain requirements as to provide suitable
support and stability for the structure.
To safety sustain and transmit to the combined deal, imposed
and wind loads in such a manner as not to cause any
settlement or other movement which would impair (weaken) the
stability or cause damage which or any part of the building or
any adjourning building.
-
It must be taken down to such a depth as to safeguard the
building against the swelling shrinkage and or freezing of the
subsoil (especially on clay soil).
-
It must be constructed to be capable of resisting any sulphates
attack and any deteriorate (harmful) matter present in the
subsoil.
2.
Floor: The floor structure must fulfill several functions and
design considerations as follows:
-
Provision of a uniform level surface; except in specified cases
for drainage purposes, floors are normally designed and
constructed to serve as a horizontal surface to support people
and their furniture, equipment and machinery.
-
Sufficient strength and stability: The floor structure must be
strong enough to safety support the lead load of the floor and
its
finishes,
fixtures,
parathions and
services
and
the
anticipated imposed loads. This is largely dependent on the
characteristic of the materials used for the floor structure such
as timber, steel or concrete. It is also expected that the floor
should be stiff and remain stable and horizontal under the dead
half of the floor structure and the imposed loads. For stability
there should be adequate vertical support for the floor structure
and the floor should have adequate stiffness against gross
deflection
under
load.
Providing
reinforcement
where
necessary.
-
Exclusion of Dampness from the inside of a building
(Ground floor),
There is usually an appreciable transfer of moisture from the
ground to the floor. To prevent this depends on the nature of
the subsoil. A concrete slab could be used on a gravel coarse
grained sand base where the water table is relatively below the
surface. A water concrete slab, where the subsoil is clay base.
-
Thermal insulation (properties): The ground floor should be
constructed to minimize the transfer of heat from the building to
the ground or the ground to the building. The hand core and
the damp proof membranes will assist in preventing the floor
being damp and feeling cold and so reduce the transfer of heat.
In some cases the floor could be insulated against excessive
transfer of heat.
-
Resistance to sound transmission and absorption (sound
insulation), Timber floors will more readily transmit sound than
a mass concrete floor, so the floors between dwellings (upper
floors) are generally constructed of concrete. The reduction of
impact sound is best affected by a floor covering sound as
carpet that readers the sound of footsteps on either a timber or
a concrete floor sound absorption of floor can also be improved
by carpet.
-
Resistance to fire:- Timber floor provides lesser period of
resistance to fire than a reinforced concrete floor. Upper floor
should be constructed to provide resistance to fire for a period
adequate for the escape of the occupants from the building
(normally 1 to 6 hours).
3.
Wall: Classification and design conveniently divide into two
categories; external and internal construction. Most external
walls support the upper floors and roof and most external wall
are self-supporting only functioning as a means of dividing
space for the building into rooms and coo pertinent it must also
fulfill other design consideration as:
 Strength and stability, the wall should sagged by carrying its
own weight and the structural loads placed upon it.
The
strength of the wall will depend on the strength of the material
of the wall and the thickness it can carry. The stability of a wall
may
affect
by
foundation
movement,
eccentric
loads
(floors/roof) acting on the centre of the wall the thickness,
lateral forces (wind), and expansion due to temperature and
moisture changes.
 To assist weather, particularly during cold and the
exclusion of rain
This depends on the exposure of the wall to wind.
The
behaviour of a wall excluding wind and rain will depend on the
type of material used in the construction of the wall and how
they are bonded. This wall must be designed so that the rain is
not absorbed to the inside force of the wall, by making the wall
of sufficient thickness, and by applying an external facing of
rendering, or by building cavity wall.
 Resistance to sound transmission and sound abortion, the wall
should be designed to resist the impact of noise. Sound is
transmitted as airborne sound and impact sound. Example of
airborne sound from radio and voices.
Example of impact
sound is slamming of a door or footsteps on a floor. The
heavier and more degree the material of the wall, the more
effective it is reducing sound. Insulation against impact sound
consists of some absorbent materials that cushion the impact of
carpet on a floor.
 Durability: The wall is designed with due regards to the
exposure of the wall to driving rain and with sensible….. it
should be durable for the anticipated life of the building and
should require little or no maintenance repair.
 Fire Resistance and thermal properties: The wall should be
resistance to collapse, flame penetration and heat transmission
during a fire (normally 1 – 6 hrs). to maintain reasonable and
economical conditions of thermal comfort in building, walls
should provide adequate insulation against excessive loss or
gain of heat, have adequate thermal storage capacity –
lightweight materials are used where loss of heat will be
encountered. While dense materials are used in continually
heated buildings.
 Roof: The structure is designed principally to prevent
penetration of inclement (severe) weather and to provide and
adequate barrier against heat loss.
Other considerations
include an adequate appearance, the facility to absorb thermal
and
moisture
strength
and
stability
to
accommodate
maintenance and rain loads expatriate.
 Door: the Fundamental purpose of a door is to provide access
into or out of a building and between the various compartments
within a building. Additionally, the following functions are to be
fulfilled, the extend depending on the building type and
purpose; the door should be designed to have sufficient
strength, shape and stability so as to provide adequate security
and privacy. A door should also function in excluding weather
(wind and rain), containing some waterproofing properties. Door
also act as barriers against fire, sound and thermal movement.
 Window: The functions of a window are to admit daylight,
provide natural ventilation and to exclude wind and rainwater. It
also acts as thermal and sound insulators. In some
circumstances, the view from a window provides an important
function as relief and pleasant relaxation from daily internal
routine (view). It contains some fire resistance properties and
can act as a means of escape in case of fire outbreak.
 Stairs: A stairway is initially designed to provide an effective
means of access between different floor levels. A secondary
function of considerable importance to provide a practical
escape route in the event of fire.
WEEK 2
SITE PREPARATION
Before the commencement of actual building construction, there is the
need to conduct certain preliminary site activities. This is to enable the
building team have foreknowledge of a site.
Some activities which
preceded the actual building construction are

Site investigation ( ) and organization (layout)

Site welfare facilities

Storage and protection of materials

Site fencing and hoarding

Site clearance and excavation

Leveling and setting out

Ground water control.
1.
Site Investigation and Organization – A preliminary examination or
survey of the job is made during the designing and post-designing
stages of a project. The survey enables the contractor or the engineer
to precisely have an idea about the site and assess if there are
peculiar problems to the proposed contract. It is this initial
understanding of these problems that the engineer will use to design
the building to suite the site. Similarly, the contractor could plan and
organize his activities, sufficiently to achieve success and minimize
time.
This is done by producing a site layout plan and placing
equipment and materials in specific positions for easy reach, handling
and utilization.
Provision of services during site organization to a building site maybe
temporary where the work is transient (short period), e.g. construction
of highways. Elsewhere the services will be a permanent necessity
and should be installed accordingly to avoid repeating the work, e.g.
building construction. It is often advantageous to the contractor to
provide these services particularly electricity and water, from where
permanent installation could be mace. Other temporary services may
include access to site, watchman services, dust control (by watering
ground area), site clean (debris clearance), etc.
SITE LAYOUT PLAN
Existing Building
Main Road
Canteen
Sub-Road
Access Road
Watchmen
Bush
Dumper
Watchmen
Aggregate
and Sand
Store and
Storage
Mixer
PROJECT
Crane
men
Dressing
Room
Tech.
Room
Engineering
Room
Clinic
Toilet
Some considerations to be given by the contractor during
reconnaissance and layout prior to constructional works are
(a)
Availability and means of access to the site whether by road,
rail or waterway.
(b)
Availability of suitable materials/equipment and spare available
for erecting plant and or storing materials around the site.
(c)
Availability of space to erect temporary site offices and welfare
facilities.
(d)
The effect of vibration on adjacent structure when the
construction involves using heavy/massive equipment (e.g. in
piling) should be considered.
(e)
The availability of water and power supply should be
ascertained and the rate of payment investigated.
(f)
Knowledge of the nature and type of soil, and the level of water
table is important as the way necessitate subsoil drainage and
cause flooding.
(g)
The local planning authorities should be approached to
ascertain whether there is any special or significant restriction
which could adversely affect the development of site (e.g.
underground cables).
(h)
Valuable information can be obtained by talking with the local
inhabitants of the area.
(i)
Any special condition that may limit work in anyway should be
noted and taken care of e.g. weather or climatic condition.
2.
Subsoil Exploration (Trial boreholes) – Trial boreholes to determined
the nature of a subsoil is an important part of an early site
investigation.
The building design and structural loading can be
related to the detailed and thorough examination of the subsoil bearing
potential (ability to withstand load). Preliminary examination may be
with trial pits excavated by spade or a hand anger.
When more
detailed information is required, a powered anger is more effective.
The depth of boreholes can be several meters deep for high rise
buildings, and boring can be at random or regular intervals. Samples of
subsoil can be extracted loose or distorted, or undisturbed in steel
tubes. They are recorded on a borehole log, and samples are then
taken for laboratory analysis to establish the moisture content, bearing
capacity and chemical composition.
3. Site Welfare Facilities – The provision of shelter and accommodation
for taking meals and deposition of clothes is a basic requirement on
all sites. The builder should provide a hut for workmen so that meals
and short rest can be taken, and also for storage of clothing not
required for work during the day and protective clothing at night. The
mass room or canteen should be convenient for washing facilities.
Adequate wash basins, troughs and showers with soaps and towels
are required. (an isolated sanitary facility with water closets is also
required). Provision for first aid is also very important, and every
contractor must provide first-aid accommodation to include a couch,
stretchers, bandages, blankets, equipment, etc a trained person in
first-aid treatment is to be available on site during working hours.
4. storage and Protection of Materials – Materials such as cement,
timbers, bricks and blocks should be protected from weather by
storing in a shed or well stacked in a suitable position on the site,
where they will not be liable to damage and are adequately protected.
Electrical and plumbing (sanitary) fittings should be kept in a locked
shed to avoid theft or breakage.
Proper storage is necessary
because saturated cement with time sets and becomes hardened
resulting to wastage. Saturation also affects the mortar or concrete
strength. Water is readily absorbed by timber causing deformation
and rot, this should be avoided. A saturated brisk or block will be very
difficult to handle. They should be well protected.
5. Site Fencing and Hoardings – A permanent fence or a temporary
hoardings will be required around the site. This is a barrier made of
block wall, wooden or mental stalk or rail or wire in some cases used
old zinc to provide security and protect equipment and materials, and
to keep out intruders. It also protections the ugly sight of construction
and preserves the beauty till completion. The hoardings are removed
after the completion of the project. The hoardings should be well
erected and in sage order so as not to cause injury to workers or
passé.
6. Site Clearance excavation to soil – The site should be cleared of the
bushes, shrubs, trees, etc. which are on the building position and
around the storage and temporary facilities area. The roads should
be grubbed up and completely removed.
Before any building is erected, it is essential that the area to be
occupied by the building has the vegetable top soil removed from site
completely or placed on one side, and spread level over areas after
completion of the project to provide gardens. The organic content of
the vegetable soil may be injurious to concrete, and so it should
never be used for backfilling, or making up levels under the building.
The path of excavation of topsoil is normally 150mm.
Leveling, land clearance and stripping of the topsoil are all easily
achieved with a bulldozer.
7. Ground Water Control: - Excavation and sample boreholes frequently
reveal and locate a level of saturation within a few meters below the
surface. This is known as the water table and it varies with season.
Excavation below the water table will be difficult and the strength of
any concrete placed in water will be seriously affected.
A pre-
knowledge of this fact helps the contractor to be equipped and
prepare with his diesel powered water pump for the temporary
removal of water during excavation and concreting.
8. Setting Out and Leveling – After the stripping of the topsoil and
general site leveling, it is important that the structure is built in the
correct position as shown on the architect’s drawings. The position of
a building is marked out with string lines and pegs to indicate
foundation trenches and walls. The frontage line (building line) is an
imaginary line shown on the site plan, or determined by the local
authority, set back from the centre line of the road way.
WEEK 3
METHOD OF SETTING OUT
There are three main methods of setting out
345 method
Builder’s square and
Theodolite methods
(a)
345 Method - This is based on the mathematical principle
that any triangle with the sides in the ration of 345 is a right
angle. The method is as follows first you determine the building
line and established one corner of the building by driving a peg
at that point. A tape is used to measure a distance of 3m along
the building lien and a second peg is established with a nail on
top. The ring of the tape is held over the second peg with the
12m mark of the tape. With an assistant and with the 3m mark
of the tape around the corner peg, the tap is then stretched out
to give the position of the third peg at 7m mark. Now a line can
then be extended through third peg to give the width of the
building. The line extended should be perpendicular or 900 to
the building line. The above procedure is also carried out for
the rest corners and any possible intersection within the
building. To check the accuracy of the four-sided figure formed,
the diagonals should be measured to be equal in length.
0.12m
3m
P2
7m
P1
Building line
a
P3
a
The diagonals (a)(a) should be equal in length
to ascertain the accuracy of the setting out
operation.
(b)
Builder’s Square Method This is similar to the 345 method, but in
this case instead of using a tape a steel builder’s square or a large
timber square and a line are used to establish the squareness of the
corners. Two pegs (P1,P2) with nails at their tops are driven along the
building line. One at the corner. A line is then held along the two
pegs tied at P1 going round the corner peg P2, the building’s square is
then held with its external angle point at nail of the corner peg, while
the line on P1, P2 is touching one entire side of the square. This line
is then pulled round P2 to touch the other entire side of the builder’s
square. Holding the line firm a third peg is the driven down where the
line touches the top of nail of P3.
TIMBER
SQUARE
STEEL
SQUARE
Nail
Builder’s Square
String line
Ranging line
P3
5
P2
P1
P1
P3
4
3 P2
Timber peg
Building line
Diagonal should
be equal
(c) Theodolite Method This is the most accurate method of setting out
of buildings. It involves using a surveying instrument called the
Theodolite. The theodolite is equipped with a telescope and cross
hair for sighting and ranging, with an internal graduated readings in
degrees for establishing bearings (horizontal and vertical angles).
The method is as follows
A
E
F
B Building line
H
C
G
I.
Mount and set the instrument at point A, sight the telescope, range
and peg out E and B to establish the building line.
ii.
Turn the theodolite screws and adjust the degree readings to 0.00.
Turn the telescope of the instrument on the tripod stand towards the
right axis until you can sight 900 00” wide. The instrument clamp sight
the telescope and range to established and peg out points F and C.
iii.
Transfer the instrument to point C, and follow the same procedure at
A, range A and F, set the angle 0.00”, turn towards the right axis to
sight and obtain 900 and to establish points G and D.
iv.
Point H could be established by using a measuring tape.
WEEK 4
EXCAVATION
Excavation in building construction is simply the act of removing or digging
out earth (soil) from the ground for the purpose of laying foundation,
construction of floor, basements, etc. The earth is originally dug up to
specified depth, width and length.
The technique of excavation is largely determined by sensitivity of the site
to vibration, intensity of work, availability of plant and the subsoil
composition.
There are basically two methods of excavation, the manual method and the
mechanical method.
The manual method involves the use of hand tools such as spades
diggers, hand augers, pickers (rakes) and other manual implements for the
purpose of excavation. The manual method is regarded as a cheap means
of excavation, it is virtually obsolete and time consuming. The method can
be used only in very small buildings, e.g. garages or house extension,
where the site is inaccessible to excavating plant, and where archeological
remains are discovered and particular care is necessary. The method is
also used for trimming excavations by mechanically means where outward
projections and deviations are specified.
The mechanical method is a process of using mechanical plant and
equipment for excavation. This use of mechanical plant and equipment
saves considerable man-hours, and are standard features on all sites. The
type of plant varies with the nature of work and the different construction
stages. Plant can commonly be used for
a.
Striping clearance and light demolition
b.
Striping of top soil
c.
Trench excavation
d.
Basement excavation
The principal types of plant machine used for excavation are
a.
Bulldozer
b.
Loader/backhoe
b.
Loader/Backhoe (Backacter) – The backachter/loader has on one
end a toothed bucket and hydraulic boom which extend out and
excavate towards the cab. This end is used mainly for excavation of
trenches, basement and ditches.
The other is equipped with a
faceshovel loader for loading excavated loose earth into a dumper, a
tipper or lorry.
c.
Scrapper – The scrapper contains a larger bowl with covered cutting
edge for stripping soil. It is used in very large sties, airfield of
highway.
Bowl
Drop d.p.r
Cutting edge
d.
Dragline/Grab Crane – Where the volume of excavation is large, the
crane- mounted dragline is preferred. The bucket is swinging forward
to penetrate the subsoil and dragged back towards the cab. Deep
excavation into granular soils is more effective with a grab or
„clamshell‟.
EARTHWORK SUPPORT
When excavations (trench) are dug in water saturated soils, it is important
to provide supports to the side of the excavation. This is done to prevent
the walls from caving-in (collapse) causing severe injury or death to those
required to work inside the trench. Apart from causing injury and death, it
will be additional cost to the builder to re-excavate and renew the damaged
work in the trench. Should the sides support collapse, timber and steel are
normally used for trench. The process of supporting trenches is generally
termed “planking and strutting”. The amount of support, side and system of
arrangement of the various timers depends on
a.
The type and nature of subsoil to be supported
b.
The depth of excavation.
c.
The length of time the trench is to remain open
d.
The time of year or climatic conditions prevailing when the trench
is excavated.
Timber is often the most convenient material for shallow trenches. Steel
interlocking polings are often used for deep water-logged subsoil.
Adjustable steel struts are also more convenient and have considerable reuse value for all depths of excavation.
The timbering members used in trench support are as follows
i.
Poling board – There are of 1.0 to 1.5m in length to suit the trench
depth, and they vary in cross-section fro 175 by 35mm to 225 by
50mm. They are placed vertically and against the soil of all the sides
of excavation.
ii.
Wallings – These are longitudinal members running the length of the
trench and supporting the poling boards. They vary in sizes from 175
by 50mm to 225 by 75mm.
iii.
Struts – These are usually squared timbers, either 100 by 100mm or
150 by 150mm in sizes. They are used to support the wallings, which
in turn holds the poling boards in position. Adjustable steel struts are
also in great use.
iv.
Sheeting – These consist of horizontal boards abutting one another
to provide continuous barrier when excavating in loose soils and
common size for the sheeting is 175 x 75mm and there is overlap of
about 150mm at the point of connection between two stages.
Alternatively, steel interlocking poling with adjustable steep struts are
used.
Wedge
Poling
Strut
Sheeting
Timbering in loose subsoil
Adjustable Steel Strut
In moderately firm ground, the timbering consists of a series of poling
boards which are widely spaced at about 60mm centres, supported by
wallings and struts. In shallow trenches, the poling boards would probably
only be needed at the about 1.8m centres with each pair of poling board
strutted individually with a single strut and no walling.
Poling Board
Walling
Strut
Timbering in Moderately Form Soil
In loose or saturated soil, a continuous horizontal sheeting supported by
pairs of poling boards and struts about 1.8m may be used. Alternatively, a
continuous length of poling boards or runners supported by walling and
struts may be used. If the trench exceed more than 1.5m in depth, it is
necessary to step up the timbering so that the lower stage fits inside the
upper section.
CONTROL OF GROUND WATER IN AN EXCAVATION
There are several methods available for controlling ground water during
excavation work. Some of the methods deals with lowering, while others
involves water exclusion from the site. Some of the methods employed in
the control of ground water during excavation work include
i.
Plumbing Method
ii.
Dewatering
iii.
Electro osmosis
iv.
Grouting
v.
Soil stabilization
1.
PUMPING FROM WELL OR (SUMP)
Pumping from sump is the most used for used of ground water
control since it is economical to install and maintain and can be
applied to all types of ground conditions.
The only problem is of the movement of the soil due to settlement
and there is also the risk of instability at the formation level of the
excavation. Where the excavation goes through permeable soil and
continued into impermeable soil, it is better to form a drain at the line
of interception to carry water in the sump. With this system a sump is
constructed at one corner of the site which forms a well point
continuous pumping of water.
The pump which is mounted on the ground level has one
disadvantage due to imitation in the design of suction lift to some
types of pumps. The suction lift of most pumps is at 7.5m – 9m. For
deep excavation where the depth exceeds 9m, the pump will have to
be placed in the excavation or on a level suitable for the suction lift.
2.
DEWATERING
This consists of lowering the water table over the area of the site and
is satisfactory for depths up to 16m, it is particularly suitable where
running sand is encountered for once the water has been removed in
the ground, the sand become relatively stable. The equipments used
for the separation comprises of
i.
Jetting pump, for driving down the well points
ii.
Suction pump
iv.
Rises pipe.
iii.
Header pipe and
The operation of dewatering is carried out by first jetting the well
points into the ground, this is done by securing each well points to
38mm diameter riser pipe at the top of which there is a connection by
a hose to the jetting pump. The assembled well points are held on
the ground and the pump operator delivers water under pressure until
the point penetrates the ground. The well points on reaching the
desired depths, the points are “sounded in” the hose of the top of the
well point is determined from the jetting point and attached to 150mm
diameter header pipe has coupling joint at 760mm 1m intervals so
that rises can be jointed at this spacing. For dealing with large volume
of water in loose ground or lose sand. The equipment can be used
for 2 main types of work.
i.
The ringing system
ii.
The
progressive
system
for
trenching.
i.
Ringing System – In this system, the building site is encircled
with needle points and for single stage work, until permit
building work to be done at depth up to 6.5m where excavation
of 9m – 12m are required 2 stage work is adopted. For this, the
top are in dewatered and excavated first, the area is then
ringed at this intermediate stage for dewatering the corner
depth.
ii.
Progressive System – This is suitable for dewatering along
the line of trenches before excavation. The wall points are with
draw when work is completed and filled in dead of the work.
The header pipe in laid along the ink of the proposed trench as
near as practicable. In different ground the pipe is placed in the
trench and supported on struts.
WEEK 5
FOUNDATIONS
A foundation is defined as, that part of a structure which is in direct contact
with the ground to which super imposed loads and dead loads are
transmitted or received.
It is also an integral part of a building which
transfers the structural load from a building safely to the ground. Many at
times, during the construction of a building, the load on the foundation
gradually increases and eventually, this will result in settlement if the
settlement is slight and uniform throughout the area of the building, no
damage will occur to the building.
But if the settlement is extensive and unequal, serious damage may result
in the form of cracked walls, distorted doors and windows and in some
cases failure may be completed by the collapse of the building.
Selection of foundation types and design depends on the total building load
and the nature and quality of the subsoil.
It is essential to achieve a
satisfactory balance between the building load and subsoil characteristics,
otherwise overstressing of the subsoil will lead to excessive building
settlement and serious structural defeats.
The purpose (importance) of foundation is to distribute the weight of the
structure to be carried over a sufficient area of bearing surface, so as to
prevent the subsoil from spreading and to avoid settlement of the structure.
A foundation should safety sustain (Carry) and transmit to the ground the
combined dead load, imposed load and wind load, without impairing the
stability of any part of the building.
A foundation is designed to support a number of different kinds of loads.
(a)
The DEAD LOAD of the building, which is the sum of the weight of
the frame, the floors, roofs, and walls, electrical and mechanical
equipment and the foundation itself.
(b)
The LIVE (IMPOSED) LOAD, which is the sum of the weights of
people in the building, the furnishings, sanitary fixtures and the
equipment they use, snow, ice and rain load on the roof.
(c)
The WIND LOAD, which can apply literal, downward, and uplift load
to a foundation.
All foundation settle to some extent as the soil around and beneath them
adjust itself to the loads. Foundation settlement in most buildings is
measured in millimeters. If the total settlement occurs roughly at the same
rate from one side of the foundation to the other, no harm is likely to be
done to the building. This is because all parts of the building rest on the
same kind of soil. But if differential settlement occur (when the building
occupies a piece of land that is underlain by two or more areas of different
types of soil with very different load bearing capacities) in which the various
columns and load bearing walls of the building settle by substantial different
amounts, the frames of the building become distorted, floors may stapes,
walls and glass may crack, doors and windows may be difficult to open,
etc. the primary objective of foundation design is to minimize differential
settlement by loading the soil in such a way that equal settlement occur
under the various parts of the building.
SOILS IN FOUNDATION
Where the foundation of a building is on rock, no measurable settlement
will occur, whereas the building on soil will suffer settlement into the ground
by the compression of the soil under the foundation load. Some settlement
on soil foundation cannot be avoided, because as the building is erected,
the load on the foundation increases and compresses the soil.
This
settlement must be limited to avoid damage. Bearing capacities for various
rocks and soils determined and should not be exceeded in the design of
the foundation to limit the settlement.
Soils are classified with regards to their size, density and nature of the
particles. Soil can be classified into three broad groups namely coarse
grained non-cohesive, fine grained cohesive and organic soils.
Coarse grained non-cohesive soil – This consist of coarse and larger
siliceous product under pressure from the loads on foundation. The soil in
this group compresses and consolidates rapidly by some rearrangement of
the particles and expulsion of water.
A foundation on this type of soil settles rapidly by consolidation of the soil,
as the building is erected, so that there is no further settlement once
building is completed.
Fine grained cohesive soils – This consists of natural deposits of the
finest siliceous and aluminous product or rock weathering such as clay.
Clay is smooth and greasy to touch, it shows high plasticity, dries slowly
and shrinks appreciably on drying. Under pressure of load on foundations,
clay soils are gradually compressed by the expulsion of water from the soil
so that the buildings settle gradually during building work and this
settlement may continue for some years after the building is completed.
Firm shrinkable clays suffer appreciable shrinkage on drying and expansion
of firm clay under grass extends to about 1 metre below the surface and up
to 4m or more below large trees. Building on shallow foundations should
not be close to trees, shrubs and trees should be removed to clear a site
for building on firm clay subsoil. This is because gradual expansion or
contraction (shrinkage) of the soil will cause damage to the building by
differential movement. This is as a result of the intake of subsoil water by
the tree roots.
Organic soils – Such as peat are not generally suitable foundation for
buildings. Foundation of this type soil are normally carried down to a
reliable bearing stratum.
TYPES OF FOUNDATIONS
There are four principal types of foundation strip, pad, raft and pile
foundations.
1.
STRIP FOUNDATION
This type of foundation is a continuous level support for load bearing
walls. It is usually made of a continuous strip of concrete of 136 mix,
and may be reinforced (126) mix for poor subsoil or high loading.
The continuous strip serves as a level base on which the wall in built
and should be of such width as to spread the load on the foundation
to an area of subsoil capable of supporting the load without stress.
The width of a concrete strip foundation depends on the bearing
capacity of the subsoil, the less the width of the foundation for the
same load. The minimum width of a strip foundation is 450mm and
least thickness is 150mm. they are suitable for low-rise construction.
Solid brick wall
G.L.
P
P
x
2P + W
SECTION THROUGH A STRIP FOUNDATION
(a)
Wide Strip Foundation
This type of foundation is used where the structural loading is very
high or relative to the subsoil bearing capacity.
It is generally
cheaper to reinforce the concrete strip to reduce the equivalent
strength thickness to carry and spread the load.
G.L.
Wall
150m
1.2m
Reinforcement
(b)
Deep Strip Foundation
This type of foundation has two applications
i.
Narrow strip or trench fill
ii.
Reinforced deep strip
The Narrow strip (trench fill) is designed to save considerable
structural construction time and where the nature of the subsoil such
as clay requires a considerable depth of 900mm, it is used to
excavate foundation trenches and fill them with concrete up to just
below the ground level say 2 brick coarse before the finished ground
level.
G.L.
900
P
400
Reinforce deep strip are acceptable alternative to wide strip
foundation for soft clay subsoil conditions. The depth should be at
least 900mm to avoid effect of shrinkage and swelling and about
400mm wide to provide sufficient support for the wall. Reinforcement
is required to take care of compressive stress as subsoil may develop
voids in long periods of dry weather due to volume change.
G.L.
Wall
900
Reinforcement
400
2.
PAD FOUNDATION
These are isolated pairs or column of brick, masonry or reinforced
concrete often in the form of a square or rectangle pad of concrete for
supporting ground beans, and in turn supporting walls.
It is very
economical to use pad foundation where the subsoil has poor bearing
capacity for some depth below the surface, rather than excavating
deep trenches and raising wall in strip foundations. It is also used
where isolated columns are specified, especially in framed buildings.
The spread of area of this type of foundation depends on the load on
the soil and the bearing capacity of the subsoil.
A
B
C
A
2
3
FOUNDATION PLAN SHOWING EXCAVATION WORK FOR PAD
CONSTRUCTION
Pad foundation
Reinforcement
Reinforcement
column
SECTION THROUGH A PAD FOUNDATION
Four members
of starter bar
Ground beam
G.L.
Mat Reinforcement
for pad foundation
building
3.
RAFT FOUNDATION
In soft compressible subsoil, such as soft clay or peat subsoil. It is
necessary to form a raft foundation to spread over the whole base of
the building. Raft foundation consists of a raft of reinforce concrete
under the whole of the building design to transmit the load of the
building to the subsoil below the raft. Relative settlement between the
foundations of columns is avoided by the use of a raft foundation.
The two types of raft commonly used are the flat raft (solid slab raft)
foundation and wide toe raft (beam and slab raft) foundation.
(a)
Flat Raft (solid slab raft) Foundation
This comprises of a reinforced concrete slab of uniform
thickness cast on a bred of blinding concrete and a deny proof
membrane, under the whole area of the building. This type of
foundation is used on loose subsoil with reasonable bearing
capacities for small buildings, such as houses.
The slab
normally reinforced top and bottom.
Cavity wall
Floor finish
50 spread (cement
& sand)
100 mass concrete
floor
G.L.
150 reinforced
concrete raft
50 Blinding
Reinforcement
(b)
Damp proofing
membrane
Wide Toe Raft Beam and slab rift ) Foundation
This is like a reinforced concrete floor with down stand beams
called toe. It is used when the ground has poor compressibility.
The reinforced concrete edge beam is designed to support the
outer skin of the brick work or columns.
The strengthened
beam collect loads from the walls or columns and transmit
these loads to the slab cast integrally with the beam, and the
slab in turn spread the loads over the whole area of subsoil
below the building.
Cavity wall
Floor finish
Screen
Reinforced
concrete
raft
Blinding
G.L
.
Damp proof membrane
Reinforcement
100 hardcore
4.
PILE FOUNDATION
Pile foundations are used where the subsoil has poor and uncertain
bearing capacity and in poor drained area where the water table is
high and there is appreciable ground movement. Piles are usually
employed because in these types of subsoil, it might be necessary to
excavate beyond 2m to meet a stable stratum. And it is uneconomical
to consider normal excavation beyond about 2m below the ground
level. The pile column of concrete either cast insitu or precast driven
into the ground to transfer the loads through the poor bearing soil to a
more stable stratum. Boring is undertaken by a powered auger. The
pile foundations are normally employed in the construction of bridges
and oil platforms on seas.
Short Bored Piles - These are used for small buildings on shrinkage
clays where adjacent trees could appreciate volume change in the
subsoil. Short bored (short length) piles are cast in holes by hand or
machine auger. The piles support reinforced concrete ground beams
on which wall are raised.
Building
Reinforced
Concrete beam
Piles
G.L.
Poor grade
subsoil
Sound bearing strata
Ground floor slab
Sand blinding
G.L.
Hardcore
Depth up
to 4m
Reinforced
concrete beam
Concrete pile
Ground floor slab
Sand blinding
G.L.
Hardcore
Reinforced
concrete beam
Depth determined
by resistance to
driving
Steel sleeve
Hollow fibre
reinforced concrete
shell
Solid concrete shoe
280
FOUNDATION ON SLOPING SITES
Walls foundation on sloping sites are normally constructed at one level or
stepped. Where the slope is slight the foundation may be at one level with
floor raised above the highest ground level. Where there is a greater slope,
it is usual to cut and fill so that the wall at the highest point does not act as
a retaining wall and there is no need to raise the ground floor above the
highest point of the site. The process of “cut and fill” is normally practiced
when providing foundation for walls on sloping sites. This is the operation
of cutting into part of the higher part of the site and filling the remaining
lower part with the excavated material or with the imported materials (for
fill). It should be noted that cutting extends beyond the wall at the highest
point to provide a drained dry area behind it.
Where a building extend some distance up an appreciable slope, it is usual
to use stepped foundation to economize in excavation and foundation
walling.
G.L.
Stepped Foundation
Foundation at one level
Steeper slope
Shallow slope
Ground
Consolidated fill
under solid floor
Consolidated fill
under solid floor
Reinforced
concrete
building slab
Selected soil
fill
Ground
bearing slab
Compacted
hardcore
Existing G.L.
Top soil removed
STEPPED FOUNDATION
METHODS OF REINFORCEMENT IN FOUNDATIONS
1.
GROUND BEAMS
Floor construction with
precast R. C. Beams bearing
on upstand beams on raft.
Reinforcements
Section through
reinforced concrete
ground beam and slab
raft with upstand
beams
R.C. Beams
Slab of raft
reinforced top
and bottom
Raised timber or
concrete floor
formed on raft
G.L.
Reinforcements
R.C. Beams
Reinforcements
Helical building
hand
Lifting hole
Press steel forms
Corner for R.C.
Main reinforcement
Stirrups to
Lifting hole
Chilled cast iron
shoe
R.C. Slab reinforced
top and bottom
Links
Forks
Section of a
body of pile
Cover
Main reinforcement
Cast iron shoe
Steel
Concrete consolidates as
the tube is withdrawn
Cage of reinforcement
Finished reinforcement
concrete pile
End of tube
Cast iron shoe
METHODS OF CONSTRUCTION OF VARIOUS FOUNDATIONS
1.
STRIP FOUNDATIONS
Construction of strip foundation is carried out by first excavating the
ground to specified volume to remove soil to receive concrete. A
fairly dry weak concrete is the placed to specified depth inside the
foundation already containing a hardcore base (if necessary). This is
to act as a working base and to receive the oversite concrete. Where
a reinforcement or mesh are required, they are placed on mortar
blocks or concrete blocks (biscuit) on the blinding to give the cover for
concrete. A leveling instrument or a building plumb and short iron
pegs (off cuts) are then used to establish the tip level of the
concreting in the trench at intervals throughout the length of the
foundation trench. Concrete is then mixed and is poured into the
trench over the reinforcement until it reaches the established pegs.
As pouring is done a potter vibrator is used to vibrate the concrete to
remove the voids from the concrete. The concrete is then left to set
and harden and cured with water after one day of easting for at least
7 days.
2.
PAD FOUNDATION
This is similar to the strip foundation construction, except that instead
of excavating in strips, deep hollow square or rectangular trenches
are dug.
The provision of reinforcement for the base of the pad
interlock with the vertical reinforcement going up for the columns.
This is to ascertain a continuous interlocking support, strength and
stability between the pad and the concrete column.
Where steel
stanchions (columns) would be placed on the pad foundation,
steel/iron bolts or steel plates are embedded in the foundation during
construction, where the stanchions or columns would be placed
(bolted or welded) on the pad foundations.
Concrete is then mixed, poured or placed, vibrated and cured as in
the strip method. In some cases formwork are sometimes used to
protect the sides and give shape to the pad.
3.
RAFT FOUNDATION
The raft system involves the excavation of the whole base area of the
building and where ground beams are specified, is further excavated
below the raft slab foundation. Formwork is made to support the sides
of the foundation and insitu slab.
The placing of reinforcement for the slab and beam interlock or
overlaps.
The placing of concrete and curing is as in the strip
method.
4.
PILE FOUNDATION
(a)
Bored Piles
This method is an insitu concrete construction. It consists of drilling
or boring a hole by means of earth drills or mechanically operated
augers which withdraws soil from the hole for casting of pile in
position. Usually steel lining tubes are lowered or knocked in as the
soil is taken out, to support the sides of the board pile.
Reinforcement are placed, concrete is then placed and compacted in
stages. As the concrete pile is cast the lining tubes are gradually
withdrawn
The disadvantages of this method are that it is not possible to check if
the concrete is adequately compacted, and there may be no
adequate cover to the concrete reinforcements.
(b)
Precast Concrete Piles
As the name implies, these are precast either round, polygonal or
square concrete, steel or timber piles which are driven into the
ground by means of a mechanically operated drop hammer attached
to a mobile piling at a calculated predetermined „set‟. The word „set‟ is
used to describe the distance that a pile is driven into the ground by
the force of the hammer.
To concrete the top of the precast piles to the reinforced concrete
foundation at the top, 300mm of the length of reinforcement of the
pile is exposed, to which the reinforcements of the foundation is
connected.
Precast driven piles are not in general use on sites in built up area
(unrestricted area) due to
i.
Difficulties in moving them through narrow streets
ii.
Nuisance caused by the raise of driving piles and vibration
caused by driving the piles may damage existing adjacent
buildings.
WEEK 6
DAMP PROOFING
SUBSTRUCTURAL WORKS
RISING AND SEEPAGE OF GROUND AND UNDERGROUND WATER
If water is to rise of seep in a wall or floor, a constant supply must be
available at the base and side of the floor and wall. Water rise by an
upward capillary pull between the masonry pores. On building sites with
high water table and on slopping sites where water may run down to the
building, site concrete, floors and walls are likely to get damp by the
respective rising and seepage or moisture/water. The obvious indication of
rising damp and seepage is the dark staining above the skirting, bored on
the interior of a wall. This however, should be carefully checked to avoid
misconception of defective plumbing, leaking gutters/down pipes, and
defective chimney. Another indication of rising damp is the appearance of
white salty deposits on both faces of a wall called efflorescence. It is drawn
from the ground as the dampness rises, and they combine with any salt in
the masonry.
Rising and seepage into building is due to the lack of provision of damp
proofing materials, or may also be due to several possible construction
faults (i.e., in the cases where damp proofing materials are provided).
Some of these faults may include the following
Earth stacked
against wall
Paving or drive
finished above
d.p.c
d.p.c
Rendering
over the d.p.c
Bridging though
mortar painting
d.p.c
The arrows
(
) indicate rising and seepage of ground
and underground water
IMPORTANCE OF DAMP PROOFING IN SUBSTRUCTURAL
WORKS
Damp roofing is the principle of preventing moisture entering buildings and
causing dampness which might be as a result of water/moisture rising up
the wall and floor from the ground forced through the structure, or seeping
through the forces of walls.
One chief essential requirement in building construction is to construct a
structure which is habitable and dry to live in. A dry building is unsightly
and causes damages to some components of the structure affected.
Most structural works are intended to be dry habitable.
Any moisture
movement upwards from the ground through the substructural works to the
superstructure hampers the functional requirements of the affected building
components, and this reduces the quality of construction. The intended
purpose/use of the structure may also be defeated. Concrete is to some
degree permeable to water and will absorb moisture from the ground. A
damp oversite concrete slab may cause deterioration and damage in
moisture sensitive floor finishes such as timber or P.V.C. A damp oversite
concrete also will be cold and draw appreciable heat from rooms causing
cold.
Damp proofing helps the prevention of moisture rising up the floor or
seeping through walls, causing efflorescence and damage to the walls and
floor finishes.
Generally, damp proofing helps to maintain the quality, strength, stability,
durability and resistance to moisture/water of structures. It also helps to
maintain an appreciable room temperature. And to provide protection to
final finishing materials to concrete floors. A damp proofing materials must
be incorporated in concrete floors.
PROCESSES OF DAMP PROOFING
The process of damp proofing involves the provision of a continuous layer
of horizontal damp proof coarse (d.p.c) at about 150mm above finished
ground level in walls whose foundation are below the ground. And the
provision of a damp proof membrane (d.p.m) for the entire area on top is
between or under the oversite concrete slab.
The d.p.c should be impenetrable and continuous for the whole length and
thickness of the wall and be at least 150mm above finished ground level.
This is to prevent or avoid the possibility of a build-up of materials against
the wall acting as a bridge for moisture seeping through the wall.
A d.p.m should be impenetrable to water and touch enough to withstand
possible damage during laying of screeds or floor finishes. Application of
d.p.m. on irregular surfaces tend to puncture the membrane, so the
application of this materials should be done on a bed of sand or ash of
12mm thickness. The d.p.m may be on top, sandiviched in or under the
concrete slab.
All d.p.c, in external walls should unite with d.p.m in, on, or under the
oversite concrete. This may be affected by either laying the membrane in
the concrete at the same level as the d.p.c in the wall or by uniting the
membrane and d.p.c, laid at different levels with a vertical d.p.c.
Cavity wall
d.p.c
50 screed
d.p.m
150 concrete oversite
50 blinding
d.p.c abd
d.p.m
Overlaps
Hardcore
Narrow trench fill foundation
d.p.c and p.p.m at same level
Cavity wall
d.p.c
Cavity wall
d.p.m
100 concrete oversite
Bed of sand or ash
d.p.m
d.p.c abd
d.p.m
Overlaps
Hardcore
Concrete strip foundation
d.p.c and d.p.m at different level
FUNCTION OF A DAMP PROOF COURSE
Damp proof course is a layer of material capable of preventing the
penetration of moisture. It is laid on top of all walls at a distance of 150mm
above the finish ground level.
A d.p.c is an unbroken layer of impenetrable material on most foundation to
prevent the moisture absorbed from the soil rising and causing dampness
in the wall. Moisture penetration and rising dampness constitutes health
risks and cause discomfort to the inhabitants of the building.
Generally, d.p.c helps the preservation of wall finishes especially at the
base of the walls. d.p.c also provides protection against the dampness
arising from during rain. d.p.c reduces the tendency of the moisture to rise
up to the wall finishes, like rendering and painting at crack blister, peel,
flake, slow drying, etc.
TYPES OF DAMP PROOFING MATERIALS
1.
Damp proof membrane materials
a.
Hot, pitch or bitumen
b.
Bitumen sheets/solutions/tar
c.
Mastic asphalt
d.
Polythene sheet
2.
Damp Proof course
a.
Flexible d.p.c materials
(i)
Lead
(ii)
Copper
(iii)
Bitumen
(iv)
Polythene sheet
b.
Semi-Rigid d.p.c materials
(i)
Slates
(ii)
Bricks
BASEMENT CONSTRUCTION
METHOD OF CONSTRUCTION
OF BASEMENT PROCEEDS IN
STAGES
1.
Excavation begins at ground level and the sides are supported by
timbering.
2.
This continues until the required dept is reached.
3.
Foundation is cast and walls started. Timbering is removed
progressively and the space backfilled.
4.
The wall reaches ground level all around the excavation.
5.
The soil inside the walls can then be removed, if necessary.
BASEMENT EXCAVATION
The excavation for deep basements started at ground level, as the holes
becomes deeper a decision base to be made about the method to be
employed.
If ramp of earth is left in position, tipper tracks can use it to get into and out
of the hole. This depends on the length of the excavation, as it must be
able to accommodate a ramp of about 200 slope. Weather condition and
type of soil may also be considered as this may affect the use of the ramp
by loaded vehicles.
The ramp may be removed finally. If this is done by an excavator, with the
soil being removed by bucket and crane, the excavator will have to be
hoisted out on completion. If vehicles cannot drive out of the excavation,
the soil will have to be loaded into buckets, hoisted to the surface and
loaded on to trucks. The excavator is finally lifted out by crane. Where
excavation is not very deep, hand excavation may be used.
Various types of earth moving and excavation plant are available for use in
different circumstances, e.g. bulldozer shovel back actions and drag-line
grab crane excavators, loader and truck.
PRINCIPLE OF TANKING IN BASEMENT WORKS
Tanking is a system of forming a continuous waterproofing lining usually in
asphalt round the walls and floor of a basement as a barrier to rising and
penetrating dampness. The term tanking can also be used to describe a
continuous waterproofing lining to the walls and floors of substructures (e.g.
basement structures) to act as a tank to exclude water. This principle is
known as Basement taking.
The traditional material for tanking is mastic asphalt which is applied and
spread hot in three coats to a thickness of 20mm for vertical and 30mm for
horizontal work. Joints between each laying of asphalt in each coat should
be staggered at least 75mm for vertical and 150mm for horizontal work with
the joints in succeeding coats. Angles are reinforced with two coats of fillet
of asphalt.
Asphalt is usually applied to the outside face of structural walls and under
structural floors so that the walls and floors provide resistance against
water pressure on the asphalt, and the asphalt keep water away from the
structure.
Where the walls of the structure are on site boundaries and it is not
possible to excavate to provide adequate working space to apply asphalt
externally, a system of internal tanking may be used.
An internal lining is rarely used for new buildings because of the additional
floor and wall construction necessary resist water pressure on the asphalt.
Internal asphalt is sometimes used where a substructure to an existing
building is to be water proofed.
HARD CORE
This is an application of suitable material suck as broken bricks, stones and
tiles, clinker, gravel, quarry waste, which are required on the building site to
fill hollow oversite concrete work. On wet sites, it may be used to provide a
firm working surface and to prevent contamination of the lower part of the
wet concrete during compaction.
The particle materials should be hard and durable, not subject to decay or
breakdown by weather or chemical attack, and it should be easily placed
and well compacted. The hardcore should be spread until it is roughly level
and round until it forms a compact bed for the oversite concrete. The
hardcore bed is usually 100 to 300mm thick. It is spread to such thickness
as required to raise the finished surface of the oversite concrete.
Generally, the hardcore bed serves as a solid working base for building and
as a bed to receive oversite.
BLINDING
Is a process of providing a layer of dry concrete, coarse clinker or ash over
the hardcore before placing the oversite concrete. Before the concrete is
laid it is usual to blind the top surface of the hardcore. The purpose is to
prevent the wet concrete running down between the lumps of broken brick
or stone, as it would make easier for water to seep through the hardcore
and could be wasteful of concrete. To blind or seal, the top surface of the
hardcore a thin layer of very dry coarse concrete can be spread over it, or a
thin layer of coarse clinker or ash can be used. the blinding layer, or coat,
will be about 50mm thick, and on it the site concrete is spread and finished
with a true level top surface.
USE OF ANTI-TERMITE TREATMENT IN FOUNDATION WORKS
A problem in tropical climates is the possibility that timber maybe attacked
by termites. The common termite or white ant forms colonies in the ground
where a nest housing the queen is found. The termites can enter a building
through the ground looking for timber to consume. The junction of the wall
and floor is a particularly vulnerable point.
There are some precautions which can be taken to reduce the risk of
termite attack.
1.
The area around the building should be inspected for termite nests,
which should b dug out and treated with insecticide.
2.
During excavation work for the foundation and hardcore bed, the
exposed soil should be treated with insecticide, in an anticipation of
termite attack.
3.
The ground floor concrete should be raised above the adjourning
ground level and should project beyond the outer wall face.
WEEK 7
FLOORS
Floors are structural parts of a building. They are usually designed to be of
either a timber or concrete work. Generally, in building construction floors
are designed and constructed for the flowing primary purposes (function):
a)
Provision of a uniform level surface: - Unless otherwise specified,
floors are constructed to provide a uniform level surface, this is done
primarily to sufficiently provide adequate support, comfort, stability
and strength to carry people, their furniture, equipment and materials.
b)
Exclusion of Dampness from inside of the building (especially
ground floors): - Floors also function as to prevent the passage of
moisture rising up/surpring through foundations/walls and causing
dampness and discoyort inside the building, this is normally attained
by using a d.p.m.
c)
Thermal Insulation: - Floors minimize the transfer of heat from the
building to the ground of the building. A floor also serves to conserve
or reduce heat as the case (situation) may require.
In this case
insulations or special finishing materials are used.
d)
Sound Insulator: - Floors also serve as a barrios to transmission of
airborne sound and reduce impact sound, (especially upper floors)
normally concrete is preferred to timber because timber readily
transmit sound than concrete where timber are used they are
normally insulated with weight material (by filling the spaces between
the timber joists)
e)
Fire Resistant: - in addition to the above functions, floors (especially
upper floor) are resistant, to fire to some considerable degree. They
provide resistance adequate for the escape of the occupants from the
building in times of fire outbreak.
f)
Compatibility with the Surface Finish: - The purpose of a floor is
also to provide an adequate and acceptable surface finish to meet the
need of the user, with regards to appearance, comfort, cleanliness,
stability and safety.
GROUND FLOORS
There are primarily two types of ground floors solid ground floor and
raised timber ground floor.
A)
SOLID GROUND FLOORS
There are normally constructed in-situ concrete. Solid concrete
ground floors have three principal components; hardcore, a damp
roof membrane and a layer of dense concrete. To construct these
types of floors, hardcore is compacted onto the reduced ground level
after excavation.
To prevent cement ground loss from the superimposed concrete
layer, or to protect a damp roof membrane from fracture, the hardcore
is blinded with a 25mm layer of sand.
The damp-proof membrane maybe positioned below the concrete
slab, upon the sand blinding polythene, sheet is the most popular
material, although bituminous sheet is acceptable. Alternatively, the
d.p.m. maybe sandwiched between the finishing their screed and the
structural concrete slab. In this particular case, cold or hot application
of bituminous solution in three layers with final layer sprinkled with
sand to bond to the screed overlay.
The concrete slab is of 100 – 150mm in thickness, composed of
cement, fine aggregate and coarse aggregates in the ratio of 1:3:6 to
provide a minimum strength specification of 1hr/mm2 at 28 days with
coarse aggregate of 38mm. A mix of 1:2:4 is preferred when using
coarse aggregate of 19mm size. A tamping bar is used to compact
and level the concrete to the specified depth-provided by short iron
pegs with finishing provided by cement/sand (1:3) screed.
B)
SUSPENDED (RAISED) TIMBER GROUND FLOORS
This system of providing ground floors in buildings is now virtually
obsolete due to the escalating cost of the materials and skilled labour
required for their installation. Some few centuries ago houses were
constructed with timber ground floors raised 300 or more above the
site concrete or earth. This was done to have the surface of the
ground floor sufficiently above the ground level to prevent them being
cold and damp during winter.
Construction of this type of floor is made up of selected timber
platforms of hardwood floor boards nailed across timber joists, and
the joists in wall plate bearing on ½B thick sleeper walls, built directly
off the site concrete 1.8 apart. Sleeper walls are generally built three
courses of brick high, and are also built honey-combed to allow fire
circulation of air below the floor, to prevent wood decay. Air bricks are
also provided along external wall also to aid the circulation of air.
Component Parts of the raised timber ground floor construction:
a.
Honey-comb sleeper wall: - sleeper walls are ½B thick built directly
off the site concrete about 1.8-2.0m apart. These sleeper walls are
generally built at least three courses of brick high and sometimes as
high as upto 600mm. The walls are built honey-combed to allow free
air circulation below the timber floor members.
b.
D. P. C.: - This is spread and embedded on top of the sleeper walls
to prevent any moisture rising through the site concrete and sleeper
walls to the timber floor.
c.
Wall Plate: - This is a continuous length of softwood timber which is
embedded in mortar on the d.p.c. The wall plate is bedded so that its
top surface is level along its length and also level with the top of wall
plates on other sleeper walls. This timber member is usually 100 x
75mm and is laid on one 100 face so that there is 100 surface with on
which the timber joists bear. The function of a wall plate for timber
joists is two-fold: (i)
It forms a firm level surface on which the timber joists can bear
and to which they can be nailed.
(ii)
It spreads the point load from joists uniformly along the length
of the wall below.
d.
Floor Joists: - These are rectangular section softwood timbers laid
with their long sectional axis vertical and laid parallel spaced from
400 to 600 apart.
Floor joists are from 38 to 50 thick and 75 to 125 deep timber boards
are laid across the joists and nailed to form a firm level floor surface.
e.
Floor Boards: - For timber, floor boards are usually 16,1921 or 28
thick and from 100 to 180mm wide and up to 5.0m in length. The
edges of the board maybe cut square or plain edged, though this
being the cheapest of cutting and fixing them, but boards tend to
shrink causing ugly cracks and the edges to open up. The usual way
of cutting the edges of floor boards is by providing a torque on one
edge and a groove on the opposite edge of each board, commonly
termed T and G. The boards are laid across the floor joists, cramped
together and nailed to the joists with two nails to each board bearing
on each joist.
f.
Ventilation using air bricks: - In order to avoid deterioration of timber
under the floor board or suspended timber ground floor, there is need
to allow air circulation under the floor system. In order to achieve this
special air bricks must be provide at the external walls of the building
and adequately spaced. The purpose of these air bricks is to cause
air to circulate under the floor and thereby preventing stagnant air
which is likely to induce dry rot fugues to grow and causing word
decay.
In summary therefore, construction of the raised timber ground floor
can be achieved the assemblage of the above conform placed on a
concrete slab on a hardcore based.
SUSPENDED (UPPER) FLOORS
There are two main types of upper floors, timber upper floors and
reinforced concrete upper floors. Though timber upper floor
construction is about half the cost of a similar reinforced concrete
floor, concrete floors are still preferred because of their better
resistance to fire and to sound transmission and supports heavier
loads.
1.
TIMBER UPPER FLOORS
There is no much difference in construction between the timber upper
floor and suspended timber ground floor.
The only noticeable
difference is the elimination of sleeper walls in the upper floors, which
consequently involved the use of layer timber section for the floor
joists.
i.
Strutting between Joists: - Timber floor joists spanning more than
3.0m are strutted at mind-span or 15m spacing to resist buckling and
deformity. This is done to safeguard and prevent cracking of the
plastered ceiling work due to excessive shrinkage and movement of
the joist. The herringbone strut arrangement using 50 or 38mm
square softwood struts is most efficient, but solid strutting is often
used for easier and quicker installation. Solid strutting consists of
short lengths of timber of the same section as the joist which are
nailed between the joists either in line or staggered.
This is not
usually so effective as the herringbone system, because unless the
short solid lengths are cut very accurately to fit to the sides of the
joists they do not firmly strut between the joists. As with herringbone,
between the first and the last joists and adjacent walls folding wedges
are used to firmly locate the strutting.
ii.
End Support for Floor Joists: - The floor is normally framed with
softwood timber joists, with maximum economical span of between
3.6 and 4.0.
The required depth of joists depends on the total load. For
stability, the ends of floor joists must have adequate support from
walls or beams. There are various methods of supporting the ends
of joists in order to sustain the imposed loadings.
a) The ends of the joists are treated with preservatives (to avoid
decay) and are built into the brick walls. This method requires
cutting and packing of trick work in order to bring the top of the
joist on the same plane, care must taken to prevent joist
protinding into the cavities of the cavity wall and providing a
bridge for moisture penetration. Alternatively timber floor joists
can be built into wall to bear on a wall plate of timber or metal,
which are along the length of the wall beneath the joists, this
assist in spreading the load from the floor along the length of
the wall and also as a level bed on which the joists are placed
and nail in position. The wall is then raised between and above
the floor joists.
b) End support for the joists can also be attained by the use of
galvanized steel floor hangers, which are built into brick or
block courses so that they project and support the ends of the
joists. This is the best method of providing supports to joist
from external walls as it avoids building timber into walls.
As an alternative to hangers, timber floor joist maybe supported by
a timber wall plate carried on iron corbels built into walls, or brick
courses corbelled out from the wall. The disadvantage of these is
that they form a projection below the ceiling.
iii.
Floor Boards: - As with timber ground floors, the boards usually
19 or 21 thick have T & G edges core cramped up and nailed
across the floor joists, with the heading joints staggered.
(ii)
GALVANIZED
STEEL FLOOR
HANGERS
Hangers built into wall
to support joists.
(iii)
STEEL CORBELS BUILT
INTO SUPPORT WALL
PLATE
Wall plate
support joists
Corbels built into wall to
support wall plats/joists.
(IV)
Two-course brick corbel
brick wall plate
WALL PLATE SUPPORTED
OR TWO CORBELS OF BRICK
CORBEL WALL PLATE
2.
REINFORCED CONCRETE UPPER FLOORS
Reinforced concrete floors have a better resistance to damage by fire
and can safely support greater super imposed than timber floors of
similar depth.
(a)
Monolithic Reinforced Concrete Floors: - As the name
implies a monolithic reinforced concrete floor is an unbroken
solid mass of concrete between 100 and 300 thick, cast in-situ
and reinforced with steel reinforcing bars.
Construction of monolithic reinforced concrete floor consists of
a temporary CONFERRING (consists of timber/steel platforms
erected at ceiling level supported on timber or steel beams and
posts) to support the concrete while it is still wet and plastic for
7 days. The top surface of the platform is then painted with
mould oil to prevent the wet concrete from adhering to the
platform, so that timber platforms can be removed easily. Small
tiles or blocks (biscuit) are then cast 15-25mm thick depending
on the specified concrete cover. These are placed at frequent
centres on the platform. These tiles (specer blocks or biscuits)
are tied to/and support the steel reinforcement, and ensures
that the mesh will have the specified cover for the concrete.
The concrete is the placed of cast on the centering to the
required thickness, and it is compacted, vibrated and leveled off
care must be taken that vibration is not overdone so that most
of the cement is hot brought to the surface, thereby reducing
the strength of the mix. The concrete is then cured for 7 days
before the centering is removed.
1B wall
Biscuit
Concrete floor
cast in-situ
Concrete floor built in
Raised brick work
above floor cast
Distribution
bars
Main bars with
bent-up ends
Timber
formwork
½B
partition
Timber
chartering
b)
Timber
support
1B wall
Precast Self-centering Floor System: - centering or formwork used
to support the monolithic reinforced concrete floors tend to obstruct
and delay building operations. So for emergency projects where time
is an important factor, self-centering concrete floors are used. This
type of floor is made of precasted concrete beams which are usually
manufactured in yards and are transported to the site for fixing. They
serve as floors when they are raised and placed in position with their
ends built into brick walls. Once in position they require is support
other than the bearing of their ends on walls or beams. There are a
wide range of precast self-centering floor systems:
i.
Rectangular hollow cross-sectional beam floor units, closed
spaced.
ii.
Inverted channel sections, closed spaced
iii.
Solid precast ‘T’ section beams with hollow lightweight concrete
infilling blocks.
HOLLOW CONC. BEAN FLOOR
WEEK 8
WALLS
Walls are vertical and continuous solid structures, usually constructed from
materials such as clay, stone, concrete, timber or metal.
Walls can be classified with respect to their functional requirements as
internal and external walls.
They can also be defined as load bearing
(carrying imposed loads from roofs and floors in addition to their own
weight) and non-load bearing (eg portion), non-load bearing is with respect
to the structural requirements. There are variably two types of walls, solid
wall and framed wall. A solid wall (Masonry wall) is constructed either of
blocks of brick, burned clay, stone or concrete.
These are laid in mortar to overlap to form a bond (bonding) or as a
monolithic (eg concrete wall). A frame wall is constructed from a frame of
small sections of timber, concrete or metal joined together to provide
strength and rigidity, and between the members of the frame thin panels of
some material are then fixed to the frames to fulfill the functional
requirements of the particular wall.
THE FUNCTION OF A WALL IS
(1)To enclose and protect a building, and also serve as a means of (2)
dividing space within a building walls serve (3) as protection against wind
and rain, and to (4) support floor and roofs and to some extent to (5)
conserve heat within the building. Walls can (6) serve to protect the
building against fire, excessive heat, and to resist or minimize the
transmission and absorption of sound especial solid block walls. Framed
walls usually of less weight than solid block walls are normally used for
partitioning existing structures so as to minimize the total load of the
building.
The use of framed walls is preferred where there is little
consideration for sound transmission. Note that no material for wall
concrete fulfils all the functional requirement of a wall with maximum
efficiency.
BRICKS
Bricks are small blocks manufactured from burnt clay that can be handled
with one hand, and its length is twice the width plus one mortar joint. Blocks
made from sand and lime and blocks made of concrete manufactured in
clay brick size are also called bricks.
The standard size is 215mm x 102.5mm x 65mm which with 10mm mortar
joint becomes 225mm x 112.5mm x 75mm.
102.5
65
STANDARD
BRICK
FORMAT SIZE
215
There are various types of bricks of the same standard format are classified
with respect to the material used, composition, extent of mixing and curing,
duration and amount of forming applied. Some of these of bricks are:
commons,
facings,
engineering
bricks,
semi-engineering
bricks,
composition of clay, flattons, stocks, marts, Gautts, clay shale bricks,
calcium silicate bricks, flint-lime bricks, and hollow, perforated and special
bricks.
Some special applications and features work require bricks to be reduced
in size or reshaped. Specials are either cut from a whole brick, or purposemade (manufactured) by hand in hardwood moulds.
½ BAT OR SNAP
HEADER
Queen Closer
½ Brick
¼ Brick
¾ BAT
KING CLOSER
¾ BAT
¼ Brick
½ Brick
1 Brick
BEVELED CLOSER
Some examples of purpose-made (manufactured) special bricks
Plink Header
Plink stretcher
Angle brick
Dogleg brick
Squint Angle
Cant
Double Cant
Birds month
Single bull nose
Half round Coping
Saddleback coping
Double bull nose
Perforated brick
bull nose mitre
Cellular pressed brick
WEEK 9
BRICK BONDING
To build or construct a wall of brick or blocks, it is usual to lay the bricks in
some regular pattern. The brick courses or rows in a wall are arranged to
ensure that each brick overlaps or bear upon two or more bricks
immediately below it. The process of laying the bricks across each other
and binding them together is called bonding. The amount of overlap and
the part of the brick used determined the pattern or bond of brickwork.
Bonding of bricks can also be defined as the arrangement of bricks in
which no vertical joint of one course is exactly over the one in the next
course above or below it, and having the greatest possible amount of lap
which is usually atleast ¼ of the length of a brick.
The main purpose of bonding is provide maximum strength, lateral stability
and resistance to side thrust, and it distributes vertical and horizontal loads
over a large area of the wall. A secondary purpose of bonding is to provide
appearance (decoration)
Brick terms in bonding: terms in relation to brick bonding
Frog or indent
Aris or Angle
Stretcher face
Header face
Tooting
Header face
Perpends
Stretcher face
Quoin
Queen closer
Bed joints
Course: - This is the name given to the row of bricks between two bed
joints, and the thickness is taken as one brick plus one mortar joint.
Quoin: - Is the external corner of a wall.
Perpends: - The vertical joints of the face of the wall. For good bond it is
necessary that these joint should be vertically above one another in
alternate courses.
Stretcher face: - This is front length and height elevation of a brick, ie 215
x 65mm face.
Header face: - the side width and height face of a brick, ie 102.5 x 65mm
face.
Lap: - The horizontal distance between the vertical joint in two successive
courses.
King closer: - these are bricks cut so that one end is half the width of the
brick. They are used in the construction of reveal to obtain rebated jamb in
openings.
Bats: - Pieces of bricks usually known according to their fraction of a whole
brick, eg ½ or ¾ bats.
Queen closers: - These are bricks made with the same length and
thickness as ordinary brick, but half the width placed usually next to the
quoin leader to obtain the required lap.
Pointing and Jointing: - Pointing is the application of a special mortar to
the horizontal and vertical mortar joint of a brick wall externally in order to
ensure that the brick joints are solidly filled with mortar to make them water
tight and secondly to give some amount of decoration to the external face
of the wall. Jointing is the method of filling brick joints in a brick wall during
the laying operations.
Flush
Keyed or curved
recessed
Squared recessed
Weathered or struck
Protruding
TYPES OF BRICK BONDS
Stretcher bond
Header bond
English bond
Flemish bond
Garden wall bond
The choice of any brick bond is influence by the following factors:
-
Prevailing environmental or site conditions
-
Thickness of the wall
-
The purpose for the wall construction, i.e. Either strength or
decoration.
Stretcher Bond: - This type of bond is where bricks are laid with every
brick showing a stretcher face or long face on each side of the wall, hence
the thickness of the wall is to be 102.5mm.
Bricks show stretcher face
Header (Heading) Bond: - This arrangement shows the header face of
every brick, smith 215mm thickness. It is rarely in use, because it has no
attractive finish (too many joints).
Bricks showing header
faces
English Bond: - This arrangement shows the bricks in one course or layer
with their header faces and in the course below and above show their
stretcher faces.
A course of bricks
showing header faces
PART OF 1B THICK
WALL LAID IN
ENGLISH BOND
Course of bricks
showing stretcher faces
Flemish Bond: - the arrangement here involves bricks in every course or
layer showing alternating header and stretcher faces. This bond is more
attractive than the English bond, because the header face of many bricks is
dark, and they are separated in this bond as against the English where they
are continuous.
Each course alternate
header and stretcher faces
show on the face of the wall
PART OF 1B THICK
WALL LAID IN
ENGLISH BOND
Garden Wall Bond: - this is suppose to have a fair finish face for both
faces of the wall. Garden wall bonds are therefore designed to reduce the
number of header faces to facilitate a fair face finish both sides in walls
where appearance is important. There is one course of header bricks to
every three courses of stretchers in English garden wall bond, and one
header to every three stretchers in each course in Flemish garden wall
bond.
Three
stretcher
faces
English
harden
wall bond
Header the
face
Closer
Stretchers
Header
Flemish
garden
wall bond
Closer
1 ½ BRICK THICK ENGLISH BOND
¾ Bat
Next upper course
¾ Bat
Queen closer
¾ Bat
One course
Queen closer
Queen closer
SINGLE FLEMISH BOND
Next course
¾ Bat
½ bats called ‘suop
headers’ used in every
other course
One course
¾ Bat
Queen closer
1½ BRICK THICK DOUBLE FLEMISH BOND
¼ Bat
Next course
Queen closer
¼ Bat
Queen closer
One course
¾ Bat
¾ Bat
Queen closer
BLOCKS
Blocks for building are wall units larger in size than a brick. They are made
of concrete or clay.
(a)
Concrete Blocks: - Are manufactured from Portland cement and
aggregates, as solid and hollow or cellular blocks. They are used
both internally and externally for non-load-bearing and load bearing
walls respectively. Concrete blocks suffer moisture movement which
cause cracking of plaster finish, vertical joints are provides in long
block walls of intervals of upto twice the height of the wall to resist the
cracking. There are three types of concrete blocks:
i.
Dense aggregate concrete blocks: - Are made from a mix of 1 part
of Portland cement to 6 or 8 part of aggregate by volume. They are
very heavy but have less unshing strength than most bricks. They
are used for general building including below the ground, and for
internal and external load-bearing walls. The standard dimensions of
these blocks are:
9”
390 to 450 long x 190 to 225 high x 215 to 225 thick.
6”
140 to 150 thick
4”
90 to 100 thick
ii.
Lightweight aggregate concrete blocks (type A): - Are made of
Portland cement and any of the following lightweight aggregates.
Granulated or foamed blast furnace slag, expanded clay or shale, or
wall-burned furnace clinker. The blocks are used in building including
below ground, in internals walls and inner leaf of cavity-walls. The
furnace clinker blocks which are the cheapest are used extensively
for walls of houses.
The foamed blast-furnace slag blocks (good
thermal insulators) are used for walls of large framed buildings
because of their lightness in weight.
Are made of the same materials as in type A. They are used mainly
non-load bearing partitions. They are manufactured as solid, hollow,
or cellular depending on the thickness of the block, the thin being
solid, and the thicker either hollow or cellular to reduce weight and
the drying shrinkage of the blocks.
SOLID
BLOCKS
HOLLOW
CELLULAR
BLOCKS
Bonding
Concrete blocks are normally laid in stretcher bond, the various thickness
of blocks are made to suit most wall thickness requirement. Bonding is
done with mortar with roughly the density, strength and drying shrinkage as
the blocks, normally 1:1:6 cement/lime/sand by volume, or 1:2:9
cement/lime/sand by volume.
Rendering: - Is normally applied to a wall for the purpose of appearance or
to improve resistance to rain penetration or both. It is a wet mix of cement
and washed very fine sand 1:3 or 4 mix, spread on the face of the wall
toweled smooth or textured to dry and harden.
(b)
Clay blocks: - Are made from selected bricks clay which are press
moulded and burnt. They are lightweight blocks, hard, dense and
hollow to reduce shrinkage during firing.
They are made or
manufactured with grooves to provide a key for plaster. They suffer
less moisture movement, are resistant to fire, and are mainly used for
non-load bearing partitions. Sizes are 290 long x 215 heights x 62.5,
75, 100 and 150 thick.
STONE MASONRY
Choice of stone for wall construction is generally limited to its availability in
the construction area. Great amount of natural stone deposits in some
parts of the country is obvious from its abundant use as external cladding in
these areas. Classes of building stone include: -
Igneous rock, formed from volcanic deposits, e.g. granite, basalt.
-
Sedimentary rock disintegrated and reformed by centuries of rock
wreathes e.g. sandstone, limestone.
-
Metamorphic rock, disintegrated and reformed by pressurization or
heat, e.g. marble, slate.
Reconstituted or artificial stone of natural stone aggregates and cement
moulded into convenient size blocks of concrete are also available.
It is a substitute for natural stone and has the advantage of freedom from
defects.
Bonding -
Stonework maybe coursed by dressing the stone to an
agreeable size of about 200mm or 300mm square. Alternatively, walls may
be constructed from stones as they arrive from the quarry. Awkward covers
are removed and the result is an uncoursed wall known as random rubble.
Snacked rubbed walling is a compromise, and is composed of squared
stone of irregular size with long vertical joints interrupted by small square
stones called ‘snacks’ of 50mm minimum dimension.
Stone cladding are also use as non-load bearing columns.
VARIATIONS IN MASONRY RUBBLE WALLING
(a) Un-coursed random rubble
200 or 300mm
(b) Coursed squared random rubble
Snacks
(c) Squared random rubble with through snacks
CAVITY WALLS
Where adequate prevention of rain penetration and improved insulation are
required, conventional cavity walls with two separate skins is provided.
This contains a half-brick outer leaf and a 90 or 100mm lightweight load
bearing concrete block inner leaf, with a 50mm wide air space between the
two leaves. The height of such walls are limited, normally between 3.5 to
9m, this is because stability is reduced as result of the two skins and there
no bonding into the thickness of the wall. The stability of the two separate
skins can be enhanced with wall ties across the cavity in such a way that
the ends of the ties are bedded in the horizontal mortar joints of each skin.
Wall ties maybe produced from galvanized steel, stainless steel or plastic.
Spacing of wall ties is at 900mm maximum horizontally and 450mm
vertically staggered with a maximum of 300mm at door and window jambs,
vertically.
To give the wall enough strength it is usual to fill fine concrete at the base
of the cavity at foundation level.
As earlier stated, the purpose of this type of wall is to prevent rain
penetrating to the inner skin and to improve the insulation of the wall.
Therefore, the cavity should be clear of obstructions by solid material, there
should be no bridge between the two skins of the wall other than the wall
ties and base fill. Any obstruction is brick or mortar in cavity may allow
water/moisture to pass through to the inner skin and so defeat the objective
of the cavity. To prevent mortar or brick from falling inty the cavity. The
bricklayer usually suspends a battern of wood, bond with sacking, in the
cavity as the wall is built. This battern is raised as the brickwork is built,
and is withdrawn and cleaned from time to time.
WALL TIES
Drip
GALVANIZED STEEL BUTTERY
GALVANIZED OR STAINLESS
STEEL DOUBLE DRAINAGE
PLASTIC
GALVANIZED STEEL
VERTICAL TWIST
PRESSED STAINLESS STEEL
Cavity wall, brick outer leaf
Cavity wall, light weight
brick inner leaf
50 cavity
Wall ties
Non load bearing tight
weight concrete block
partition 1 bonded to
external wall with metal
wall ties
d.p.c.
G.L.
Screed
dpm
Hard core
Foundation
Over site concrete
WEEK 10
PARTITION WALLING
Internal walls usually called partitions principally serve to divide the gross
floor area of a building into compartments or rooms. A secondary purpose
is to transmit floor and/or roof loads to a suitable foundation.
Simply put the functions of partition walling is (1) to divide space within
building, (2) sometimes to carry and transmit loads to the ground (3) it can
also serve as a barrier for sound transmission and (4) for privacy.
The constructional forms (types) of partitions are:
(1)
Concrete block
(2)
Clay block
(3)
Timber frame or stud
(4)
Demountable frame
Concrete block partitions
Are normally used for both load-bearing and non-load bearing partition
walling, the minimum thickness of load-bearing partition block work for
single and two-storey housing is 90mm, while for three storey is 140mm.
Stability is achieved at the base by independent strip foundation or a
thickened area of reinforced ground floor slab.
Where the wall occurs in an upper storey, base support is achieved by a
beam. Stability at the ends of the block wall is by creating pockets or
recesses in the existing wall as it is built alternative course are then bonded
into the inner leaf. Metal ties can also be used at the T-Junction of
subsequent courses of the existing wall end the new partition. Non-loadbearing block partitions are less strictly controlled and maybe of minimum
thickness of 60mm. Block for this purpose should not require a foundation
in excess of the ground floor concrete. Walls are bonded or tied as in the
case of load-bearing partition walls. Openings in load bearing or dense
concrete block partitions will require a lintel at the door/window head.
External wall
Alternatively using
expanded metal ties in
every joint
Partition
Alternate courses built
into inner leaf or
pockets of existing well
1ST COURSE
2ND COURSE
3RD COURSE
TIMBER FRAME OR STUD PARTITION:
These are a lightweight wall system, generally non-load bearing. They are
constructed directly from the floor and will require no special structural
support, the frame construction contains a vertical studding at 400 to
600mm spacing with noggins at approximately 1m spacing to restrain
movement. Noggins are staggered to simplify nailing through the stud, and
door openings are provided with thicker studs to form jambs or posts. The
framework is clad with timber boarding or sometimes sheet metal.
Plasterboard of 9.5mm thickness is the most popular, offering economy
with choice of painting, plaster or paper hanging for finish treatment, sound
or thermal insulation maybe improved by filling the framework gabs with
insulation bats.
100 x 50 head of
partition
100 x 50 stud
between 400 to
600 spacing
Folding wedges
100 x 50 Noggins
(approx for spacing
to avoid movement)
100 x 50 sill
or soleplate
Floor Board
Floor joist
100 x 75 head
room and posts
100 x 50 stud
100 x 75 Door post
Door dinning
Door
9.5mm plaster board
Door Stop
Insulation
DEMOUNTABLE FRAME PARTITION
Demountable frames are a non-load bearing scheme suitable for use in
office and commercial buildings. They suit this type of building, as change
sin office layout or changes in occupancy can easily be achieved without
structural disruption. This system is based on a framework of lightweight
galvanized steel channel fixed to wall, ceiling and floor with plugs and
screws. Wallboard of plaster, chipboard or plywood is secured y selflapping screws at approximately 1m vertical spacing to the channels and
intermediate studs spaced every 600mm. Joints between boards are
closed with a steel cover strip secured every 250mm and a plastic capping
trim.
Channel set back for
timber door post
Galvanized steel
vertical channel @
600mm spacing
Self tapping screws
at 1m spacing
Wall board
Cover strip and
plastic trim
50m will sill (and
head)
TIMBER WALLS
Construction of a timber framed wall is a rapid, clean, dry operation often
accomplished by the use of simple hand or power operated tools. When
sensibly constructed it has adequate stability and strength to support floors
and roofs of small building. And when covered with wall finishes it has
sufficient resistance to damage by fire, good thermal insulating properties
and reasonable durability.
Timber framed walls consist of small section timbers fixed vertically to suit
the loads to be supported and materials to be used as weathering and
facing, fixed to a bottom sole plate (secured by bolts embedded in
foundations), and a top member head plate to form the traditional timber
stud frame.
The simple timber stud wall with the vertical suds nailed to the sole and
head plates are provided with diagonal timber braces built into the frame to
provide sufficient rigidity.
Sheathing of boards or plywood panels are used to cover clad these
frames. They are properly secured to the studs, sometimes with insulation
boards fixed between studs.
Sheathing of boards or plywood are sometimes used as tracings, because
the wall is dry it adviceable to use systems of dry finishes and livings, such
as plasterboard and boards. To provide sufficient thermal insulation and
prevent moisture it is necessary to fix an insulating material and vapour
barrier between the studs with vapour barrier fixed between the used of the
building and the insulation.
OPENING IN WALLS
Openings in internal and external walls are for mainly the provision of
windows and doors; these are usually required for access, privacy,
ventilation, outside view etc.
Head of opening
Jamb of
opening
Jamb
Soffit
Sill of window or
threshold of door
opening
Reveal
Jambs: - Is the term used for the full height of opening either side of the
window of the brickwork.
Reveal: - Describes the thickness of the wall revealed by cutting the
opening and the reveal is the surface of brick work as long as the height of
the opening.
Sill: - Is the lower part of the opening for windows.
Threshold: - Lower part of opening for doors.
Soffit: - In the bottom part of head or top of opening.
Jambs of opening for windows and doors in solid and cavity brick and block
wall are mostly finished with plain or square jambs. Where the window and
door frames are made of soft wood, to hide as much of the window frame
as possible as a partial, protection against rain or appearance sake the
jambs of openings are REBATED.
Solid wall
Rebate or recess
Inner reveal
Outer reveal
Sill of window or
threshold of door
opening
External face
of wall
Jambs of opening in cavity walls must be well closed to prevent cold air
blowing into it and so reducing the insulating properties of the wall, and any
material used to close the cavity must be non-absorbent to prevent
movement from the outer to the inner skins. There are two ways of closing
the cavity of jambs of openings:
a.
By solidly closing the cavity with brick or block and building in a
continuous d.p.c., or
b.
By building in the timber or metal door or window frame so that it
closes the cavity.
Head of Openings: - The brickwork or block work over the head of
openings (soffit) has to be supported either by a flat lintel or an arch.
Lintel: - Is any single solid length of concrete, steel, timber or stone built in
over an opening to support the wall above it.
Bearing
ends
Depth
Lintel
Window or door opening
The ends of the lintel are built into the brick or block work over the jambs so
as to transmit the weight carried by the lintel to the jambs. The area on
which the end of lintel bears is termed its bearing ends. The wider the
opening the more load the lintel has to support and the greater its bearing
at ends must be so as to transmit the load it carries to an area capable of
supporting it.
Casting lintels: - Lintels which are most cases rectangular in section,
could be ‘precast’ (cast inside a mould and hardened before it is built into
the wall) or cast insitu or situ-cast (cast in position inside a timber mould
fixed over the opening in walls).
A modification of the rectangular section lintel, known as a BOOT LINTEL,
is used to reduce the depath of the lintel exposed externally and to improve
appearance.
A boot lintel has its toe part usually 65 deep showing externally. A boot
lintel can be used over openings in a cavity wall only where the wall has an
internal insulating linings this is to resist the lintel from acting as a cold
bridge.
R.C boot lintel
Brick cut to
¼B thick
Toe behind
brickwork
face
Weathering
65
Toe of boot
lintel
Boot
lintel
Boot
lintel
65
Insulation
Throat
Drip
Lintel in Cavity Wall: - It is important to carry the thermal insulation cavity
fill or timing applied to the inner skin down to the head of the opening so
that whole wall is insulated. This is to ensure that the lintel does not act as
a cold bridge due to it’s poor insulating properties and could invite
condensation on its inner face.
There are also galvanized steel lintels
designed to support both the outer skin and a course of lightweight
concrete blocks over the lie of openings.
Cavity
Brick
outer leaf
Insulation
board fixed
carried down to
lead of opening
Light weight
block inner skin
Brick
rater leaf
Dense conc.
Block inner
Conc. Lintel
Galvanized steel
lintel built into
jambs to support
bricks and block
skins of cavity
wall
R.C. Lintel
50
235
Light section
galvanized steel
lintel
229
Heavy section
galvanized steel
Brick Lintels: - Maybe formed as bricks laid in mortar horizontally over
openings. It gives poor support and usually need additional support. There
are various methods of strengthening and giving support to brick lintels.
For openings upto 900mm wide, it is satisfactory to cut the brick at either
end of the lintel on the splay so as to form a ‘skew back’. For openings
more than 900 it is supported by a wrought iron bearing bar, with end built
into jambs and on which brick lintel bears.
Also when using fine grained bricks (Marls or Gaults) for lintel a hole could
drilled in each brick of the lintel. A mild steel rod is threaded through the
holes and the ends built into the brickwork on either side of the lintel.
Wall ties bedded between bricks and cast into an insitu lintel behind it could
also be used as support in recent years a galvanized steel support for brick
lintels has been used, mainly for internal walls.
Brick lintel
Concrete
lintel
Skewback
Brick lintel with
skewback at jambs
Concrete lintel cost behind
brick lintel to that the ties
are cost into it
Wall tie
50 x 6 iron
bearing with
ends built into
jambs
Internal
brick or
block wall
or partition
Galvanized
lintel built
into jambs
Brick lintel built with the
ties bedded between them.
100mm wide lintel
Lintel conc.
with timber
trimming
Brick Arches: - Are structures composed of serve aints of brick or stone,
used as alternative, to a lintel to support the load over an opening. Arch
shapes may relate to many attractive geometrical forms, the most common
being the semicircular.
Crown
Haunch
Extrados
Abatement
Intrados
Haunch
Springing point
Intrados and Extrados: - The inside and outside lines of curve of an arch.
-
Soffit – Is the inside curve surface under the arch.
-
Crown – the middle third of the arch.
-
Haunches – two lower thirds of the arch.
-
Abutment-where the plain brickwork meet the extrados of the arch.
-
Springing line – the horizontal mortar joint or line from which the
arch springs.
-
Voussoir – word used to describe each brick (or stone) used to
form an arch.
WEEK 11
STAIRS/STAIRCASE
A stair is the conventional means of access between floors in
buildings. Staircases provide a safe, easy, comfortable and
serviceable means access from one level (floor) to another in a
building. The width of a stairway is normally between 600 – 900mm
TYPES OF STAIRCASES
(a)
Straight Flight (Collage) Staircase: - A straight flight stair
rises from one floor to another in one straight direction within or
without an intermediate landing.
Landing
First floor
Landing
Second floor
Flight
(b)
Quarter Turn Staircase: -
A quarter turn stair rises to a
landing between floors, turns through 900 then rises to the floor
above.
1
¼ turn
(c)
¼ turn
Half Turn Staircase: -
A half turn stair rises to a landing
between floors, turn through 1800, then rises parallel to the
lower plight, to the floor above. A half turn stair is also referred
to as a ‘dog leg’ stair.
½ Landing
2
½ Landing
(d)
Geometrical Staircase: - Consists of two types; the spiral
(helical) and the elliptical stairs. They are usually constructed
write treads tapered on plain.
The spiral or helical stair is
economical, it take up little floor area, but difficult to use and
impossible for moving furniture and equipment.
The elliptical stair is extravagant in the use of space and can
provide an elegant feature for the grand building.
Hard rail
Dancing step
EXAMPLES
Spiral (helical)
stair
Elliptical stairs
3
*
Material for Stairs
Stairs maybe constructed of timber, stone, enforced concrete
and steel.
*
Terms of Stair Construction
12m min.
headroom
1.5m min
clearance
Newel post
Hand rail
900mm
minimum
Rise (Max.
220mm)
Total rise or
rise of flight
Pitch line
Max. 420
840mm – 1.0m
Going (min.220mm
Total Going or
Going of flight
Maximum gab between
galvanizers
Steps: - Are a series of short of a horizontal face called tread and a
short height vertical face called riser, placed together at 900 or
constructed to form a structure in series where people can use to
ascend or descend the staircase by placing their feet on the treads
with the vertical risers providing the slope.
4
Flight: - An uninterrupted series of equal steps between floors or
between floor and landing or between landing and landing. The usual
of unobstructed width of a flight is from 800 for houses to 1200 for
hospitals/school 600 is acceptable if access is to be one room only
(normally bedrooms).
Tread and Riser: - As described above, the horizontal surface of a
step is described as the tread and the vertical or how vertical face as
the riser. Treads in enclosed steps usually project beyond the face of
the riser as a nosing to provide as wide a surface of tread as
practicable, and protect the tread against wear.
Rise and Going: - Rise is the distance measured vertically from the
surface of one tread to the surface of the next, or the distance from
the bottom to the top of a flight (total rise or rise of flight).
Going is the distance measured horizontally, from the face of one
riser to the face of the next riser, or the distance from the face of the
bottom riser to the face of the top riser of a flight (total going or going
of flight) are of sufficient width to contain and support the treads and
risers of a flight of steps. Usually the ends of the treads and risers are
glued and wedged into shallow grooves cut in closed strings. The
grooves are cut 12mm deep into string and tapering slightly in width
to accommodate treads, risers and the wedges which are driven in
below them.
5
Staircases are usually enclosed in a stair well, formed sometimes by
an external wall(s) and partitions, to which the flights and landings are
fixed. The string of a flight of steps fixed against a wall or partition is
called wall string and the other string the outer string.
Half space landing
Newel post 100 x 100
Hand rail 75 x 50
Skirting
Floor boards
Balusters 25 or 19
100 x 50 landing
joists built into
walls
33 x 44 thick wall strings
Section of 32
tread and 19
risers
12m deep housing
in 250 x 38 string
for tread, risers
and wedges
175 x 75 trimmer
support landing joist
and newel post bolted
to it.
Foot of newel post
bolted to floor joist.
Tread and risers
loused 12mm in close
outer string.
Floor boards
Foot of newel post
bolted to joist or raised
timber ground floor.
6
Foot of outer string
tonored and pinned to
newel post.
The provision of strings can be done in ways; close or closed strings
(as above) and open or cut string.
Close or Closed Strings is the method whereby the string encloses
the treads and risers it supports. It looks happy and does not show
the profile of the treads and risers it encloses.
Open or cut string improves the appearance of a staircase; the outer
strings are cut to the profile of treads and risers.
25 square balusters
dovetail house in tread
Painted rising
Screws
Cut outer string
38 x 38 brachct screwed to
tread and string
To strengthen the right-angled joints beneath, between treads, risers
and string, angle blocks are used. Angle Blocks of triangular section
of softwood 50square timber and120mm long each, are glued in the
internal angles between the underside of the treads and riser, after
7
the have been together and glued and wedged into their housing in
the string.
Risen
Tread
Angle
block riser
Riser
Tread
Angle between
50square, 120 square
*
Pitch:- This is the angle of inclination of the stair from the
horizontal, usually between 1500 to 4200.
*
Head Room and Clearance: - For people, goods, and furniture
is normally between 1.5m to 2.0m, measured vertically between
the lias of nosing or pitch line of the stair and the underside of
the stair, landing and floors above the stair.
*
Summary of controls affective stair construction
-
Equal rise for every step or landing.
-
Equal going for every parallel tread.
-
Maximum pitch angle to the horizontal is 420.
-
Going of a tread should be atleast 220mm (Going, G  220mm).
-
Rise of a tread should be atleast 75mm and no greater than
220mm (Rise, R = 75 to 220mm).
8
-
Headroom measured vertically above the pitch line is atleast
2.0m.
-
The sum of twice the rise plus the going is equal to or between
550mm and 700mm (2R + G = 550 to 700mm).
-
Unobstructed width of stair, excluding the string, is atleast
800mm. 600mm is acceptable if access is to be one room only,
provided it is not a living room, Kitchen, bathroom or water
closet.
-
There shall not be less than two (2) and not more than sixteen
(16) risers in a flight.
-
Handrails are not required for the bottom two steps, thereafter
are provided at a height between 840mm and 1.0m above the
pitch line, and atleast 900mm around the landing.
-
Balusters are spaced at 100mm to prevent a 100mm diameter
sphere passing through.
TIMBER STAIRCASE
Timber staircase is one in which a stair with treads and risers are
constructed from timber boards and put together in the same way as
a box or case. The members of a timber staircase flight are mainly
strings or stringers tread and risers. Timber members are normally
cut of the following sizes: treads 32 or 38, risers 19 or 25, strings 38
or 44. Because the members of the flight are put together like a box,
9
thin boards can be used and yet be strong enough to carry the loads
normal to stairs.
The usual method of joining risers to treads is to cut tongues on the
edges of the risers and fit them to grooves cut in the treads. Treads
are secured to the risers with screws, so as to prevent tongue coming
out of the groove by the action of peoples’ weight on the tread.
Nosing on treads usually projects out at about 32mm, or the
thickness of tread, from the face of the riser below. It rounded for
appearance purpose.
Strings (Stringers) cut from 38 or 44 thick
Landings: - A half and quarter space (turn) landing is constructed
with a sawn softwood trimmer which supports sawn softwood landing
joists or bearer, floor boards and newels or newel pests. Newel posts
cut from 100 x 100 timber and are notched and bolted to the trimmer,
serve to support handrails and provide a means of fixing the ends of
outer strings.
Balustrade: - The traditional balustrade consists of newel posts,
handrail and timber balusters the arrangement of these three
components is termed open balustrade. When the space between the
handrail and a close string is enclosed with timber panels, plywood,
hardboard, glass or any sheet material fixed to the light framework,
the balustrade is then termed close (or enclosed) balustrade.
10
Handrails: – Cut from 75 x 50 timber are shaped and moulded, have
their ends tenoned to mortises in the newels. For domestic buildings
the minimum height of handrails above the line of nosing is 840mm
vertically, and for other stairs 900mm.
Balusters: - May be 25 or 19 square or moulded. They are either
tenoned or housed in the underside of the handrail and tenoned into
the top of closed string or set into housing in the treads of flights with
cut strings.
The triangular space between the underside of the lower flight of a
stair and the floor is called the spandrel. It maybe left open or filled
with timber framing as spandrel panel.
To provide support under the centre of treads and also for fixing
plaster boards a sawn softwood carriage below flight of a staircase.
The fir (softwood) carriage is fixed under the centre of a staircase
with brackets nailed each side of it and under the stair to reduce
creaking.
Winder: - is the name given to tapered treads that wind round quarter
or half turn stairs in place of landings to reduce the number of steps
required in the rest of the stair and to economies in space. The
winders are supported on bearers housed in the newel post and the
well string built up from two boards to house treads and risers.
Winders are not recommended for the young and elderly and not for
rise and means of escape.
11
Open balustrade 75 x 50
hand rail 25sq. balusters
100 X 100 newels
Newels drop
Fix carriage
Apron
Newels
100 x 90
joists
Newels
Risers 25
175 x 75
trimmers
Spandrel
panel
Treads 32
Fool of Newel post bolted to floor joists
Carriage
First floor
landing
Open well
PLAN
12
Trimmer
Joist
Newels
Newel 100 x 100
Handrail 75 x 50
Stile of paneled
balustrade 100 x 32
Top-rail of paneled
balustrades 100 x 32
Three ply panel set in
grooves in rails and
stile of paneling
Bottom rail 100 x 32
Capping to string
75 x 18
Close outer string
250 x 50
Newel post
String
Spandrel
Bullrose bottom step
(quarter circle turn
String
Newel post
Spandrel
Rounded bottom step
(half circle turn)
13
Top of carriage fixed to
trimmer or landing joists
175 x 75 rough brackets
nailed to carriage to
support centre of width
of treads.
100 x 75 carriages fix
Bottom of carriage
fixed to 100 x 10 plates
miled to floors
Open Riser Wood Stair: - Open riser a ladder stair consists of
strings with treads and no risers so that there is a space between the
treads, the strings maybe either close or cut to outline the treads. The
treads cut from 38 or 44 thick timbers are housed in closed string,
secure in position with glued wood dowels. 10 or 13 diameter steel tie
rods, one to every fourth tread are bolted under the treads through
the string to strengthen fixed tread to the strings against shrinkage
and twisting. The strings are fixed with bolts to sides of strings and to
the trimmers. Where deeper strings are cut to provide a seating and
fixing for tread, the tread are screwed to the cut top edge of the
strings. Open riser wood stair are constructed as straight flight stairs,
and no newel posts for handrail inzing. Handrail and balustrade are
fixed to the sides of the strings.
14
Close string
Close string, free
stranding or screwed
to plugs in wall as a
wall string
Tread
housed 13
deep in
string and
glued
13 diameter
steel tie rod
bolted string
Trimmer
String bolted to trimmer
with angle plate
Tie rod
Waist
Outer string
Metal standard bolted
to side of string
Cut string
Handrail bolted to
standards
Galvanized steel plate
bolted to string and to
the solid ground floor
Treads bear on and
are secured to cut
string with screws.
CONCRETE STAIRS
Generally reinforced concrete stair has better resistance to damage
by fire than timber staircase. The width, rise, going and headroom
and the arrangement of the flights of steps as straight flight, quarter
turn, half turn and geometrical stairs is the same as for timber stairs
and concrete stairs. The usual form is as a half turn (dog leg) stair. A
simple reinforced concrete stair has a similar structural behavior to a
simply supported floor slab.
Formwork: - The underside contains a 25mm inclined plywood sheet
supported on joists and struts. Steps are formed by securing boards
15
to the adjacent walls and suspending cleats and riser boards at the
required spacing. Where walls do not occur, an open string maybe
formed by using edge formwork cut to the stair profile. Reinforcement
spacers should be used to provide at least 20mm concrete cover.
Reinforcement of a concrete stair depends on the system of
construction adopted and provisions. Usually the main reinforcement
of the landing is both ways across the bottom of the slab,
150 x 38 board
secured to wall
38 x 50 riser board
75 x 50 cleats
100 x 50
transom
100 x 75 or steel
props
Struts and braces
Adjacent wall
25mm plywood
Bracketing and
cleats to 100 x 50
Folding wedges
joists
16
Riser board
Plywood decking
Concrete
Joists
Edge formwork
and the main reinforcement of the flights is one way down the flights.
Bar extends out of the slab to provide reinforcement continuity.
Concrete should be very of compressive strength 25 – 30n/mm2
conforming to a mix ratio of 1:1½:3. The effective depth of the
inclined slab that forms the flights is at the narrow waist formed on
section by the junction of tread and riser and the soffit of the flight. It
is this thickness that has constructional strength and the steps play
no part in supporting loads.
The minimum of 20 cover for
reinforcement is to protect the bars or steel red against five.
17
Metal balustrade
50 x 6 convex rail
st
1 floor landing
40 x 5 rails
SECTION A.A
20 sq.
standards
12mm rods @ 150 C
12mm across flight
one to each tread
12mm rods @ 150
C/C across width
and length of
landing
Landing bears
½B in wall
Concrete
cover
12mm rods @
150e/c
Slid grd. floor
Half space
landing built
into stair wall.
12mm rods @ 150
C/C across lav of
landing
12mm rods @ 150 along the
length of flight, and one
across each tread.
Precast Reinforced Concrete Stairs: - Stairs cast insitu are
considerably more difficult to create than columns, beams and floors.
The irregular shape and inclined soffit create difficulties which
consume considerable formwork production time. Precast stairs
compatible with precast floor systems, particularly as lifting
equipment is on site and as the need for formwork would break the
construction routine by requiring carpenters at intermittent stages.
Where precast stairs are used with insitu concrete floors a recess is
18
left in both top and bottom floor slabs to accommodate a step left in
the stair.
Recess
Recess
Precast Concrete Steps (Recess): - These are generally used as
an entrance feature with direct bearing on the ground-support is at
either end and reinforcement minimal.
This type of steps are
normally constructed of short flights for entrance where the height of
an entrance door is considerably higher than the ground level.
½B wall
Optional open string
250 x 150mm precast
concrete steps
Open rise alterative
using purpose made
steps or paring slabs
225 x 150mm
concrete steps
19
Spandrel Cantilever Steps: - These are steps built into a wall at
one end only and receive no outer string support. As only one end is
supported, a minimum of 225mm or one brick thick wall hold is
necessary. Temporary support during construction is required at the
free end, at least two 16mm diameter steel reinforcing rods are
provided close to the upper surface to resist the bending stresses
imposed by the cantilever situation. An alternative application uses
precast tapered treads centred on a steel tube to create an open riser
spiral stair, with two 16mm diameter steel balusters on every tread to
support a tubular steel handrail.
225mm wall hold
16mm steel rods
1granite aggregate
concrete 1:1½:3
900mm
CANTILEVER STEP SECTION
Steel axis tube
15mm mild steel
rod baluster
Precast, R. C. tread
Mild sleeve
around baluster
OPEN RISE SPIRAL STAIR
20
Week 12
ROOFS
The roof structure serve principally to prevent weather penetration and as a
barrier against heat loss. The roof structure is broadly classified into two
groups, flat roofs and pitch roofs. Roof structures are classed according to
the interrelationship of components which make up their framework as
follows: Single roofs, double roofs, triple roofs, trussed rafters.
Materials employed or used for the construction of roofs are basically timer,
concrete, and steel. Most pitch roofs are normally constructed of timer or
steel, possibility of flat roofs in timber and steel still exist. Consequently
most roof structure in concrete are constructed as flat roofs.
The figure below shows a combination of roof formations. This unlikely
arrangement indicates constructional forms, components and allied
terminology which must be noted.
Common rafter
Ridge board
Cripple rafter
Valley rafter
Purlin
Ridge
Verge
Hip rafter
Gable
end
Leanto roof
Crown rafter
Hipped end
Flat
roof
Jack rafter
Wall plate
Hipped end is where the roof slope is continued around the end of a
building, whereas the wall is carried up to the underside of the roof at a
gable and hip rafters frame the external angles at the interaction of roof
slopes, while valley rafters are used at internal angles. The shortened
rafters running from hip rafters to plate and from ridge to valley rafters are
termed jack rafters, while full-length rafters are often called common
rafters.
The bottom portion of the roof overhanging the wall is known as the eaves.
Where the roof covering overhangs the gable end, it is termed the verge
purlins are horizontal roof members which give intermediate support to
rafters.
Rafters are splay cut or beveled and nailed to the ridge board at the upper
end and bird mouthed and nailed to the wall plate at the lower end.
Roof slope is usually in degrees, whereas the pitch is the ratio of rise to
span. The rise is the vertical distance between the ridge and the wall plate,
while the span is the clear distance between walls.
In a half pitch or
‘square pitched’ roof, the span is twice the rise, Eg. 3.5m rise with a 7m
span.
SINGLE ROOFS
Single roofs are produced in a variety of forms, all having the common
property of two-dimensional support, except at ridge board and wall plate
levels. These roofs are simple in design and include; lean-to roofs, couple
roots, close couple roofs and collar roofs.
Lean-to roof: - This is a simple form of roof with support at one side on a
main structural wall and at the other side on an independent wall. This is
where the wall is carried up to a higher level than the other and the rafters
bridge the space between. It is suitable for outbuildings and domestic
garages with a span not exceeding 2.5m. The upper ends of rafters are
supported by a ridge board plugged to the wall or a plate resting on embed
brackets
Couple roof: - Contains pairs of opposing rafters supported by wall plates
and with a central ridging from ridge board. In absence of a tie they are
weak, the rafters exert an outward thrust to the walls, and this type of roof
is therefore restricted to a span of about 3.5m. This limits their application
to small garages, sheds and similar single-storey building.
Close couple roof: - In close couple form the span potential is greater with
introduction of ceiling ties. This takes care of any deflation up to a span of
4.5m, from where an intermediate support to the rafters will be necessary.
Collar roof: - The collar roof is a variation of close-couple with the ceiling
tie raised. This roof form economies in brickwork by utilizing part of the
roof space for accommodation. Collars are joined to rafters with dovetail
halved joint to give increased-strength.
Common rafter 50 x 100
LEAN-TO
Wall
Plates 100 x 1/5
Span  2.5m
Ridge Board 38 x 175
Common rafter 50 x 100
COUPLE
Rose
Ridge Board 38 x 225
Common rafter 50 x 125
CLOSE COUPLE
Collar 50 x 125
Ridge board 50 x 125
Common rafter 50 x 125
Do retailed halved joint
Collar 50 x 125
COLLAR
1
/3 Rise
Double roofs: - Spans beyond 4.5m may also be achieved by increasing
the sectional area of the rafters and ties. At little over 5m the necessary
size of timber becomes uneconomical in comparison to introducing
additional members within the roof space.
This is the use of a third
dimensional unit known as a purlin which runs parallel to the wall plate and
ridgeboard. The purlin supported by struts, collars and hangers at every 4th
rafter, provides support to the rafters.
Ridge board 38 x 175
50 x 100 com. Rafter @400 e/c
Purlin 50 x 150
Binder 50 x 100
100 x 50 Hanger
Structural
partition
Triple roofs: - The principal components are prefabricated or siteassembled trusses spaced at 1.8m to support purlins and ridgeboard.
Varying designs offer an uninterrupted span potential of between 5m and
11m. Assembly is by simple bolted connection with toothed plates.
Ridge Board
Cover plate
Purlin
Rafter
Binder
Wall plate
Stout
Ceiling tie
Trussed rafters: - These are a series of triangular trusses which have
gradually superseded the use of bolted trusses in domestic roofing. They
have the advantage of quality-controlled factory prefabrication with quick
and simple site installation. Members are secured with galvanized steel
nail plates. Precise span limits are difficult to define; to they depend on roof
pitch, loading and arrangement of internal bracing. Most manufacturers
offer a standard range of trusses of 12m span with pitch variations between
150 and 350. Purpose made designs are possible for larger spans and
steeper pitches.
Some basic, popular truss patterns are shown below,
these are for modest span/loading requirements with symmetrical centreline location of bracing relative to the spans.
STANDARD TRUSSED RAFTERS
FINK OR
SYMMETRICAL
KINGPOST
FAN
ASYMMETRICAL
MONOPITCH
ATTIC
DORMER
WEEK 13
FLAT ROOFS
Flat roofs in timber:
Construction of these types of roofs is similar to that of a timber upper floor.
Timber flat roof generally consist of softwood timber joist 38 to 50 thick and
75 to 225 deep placed on edge 400 to 600 apart with ends built into, onto
or against brick walls and partitions. The joists are strutted using solid or
herringbone strutting methods. End support for joists is achieved by
building their ends into the inner skin of the wall, or supported on metal
hangers, metal wall plate or corbels, same as in upper floor construction.
To attain the required slight slope or fall for rainwater outlet in timber flat
roof construction, timber firing pieces or tapering timber pieces are used. It
consists of either tapered lengths of fir (softwood) nailed to the top of each
joists or varying depth length of fir nailed across the joists.
Tapered firing pieces
nailed to top of joists
Varying height firing
pieces nailed across joists.
To board timber flat roofs, roofs boards usually 19mm thick with rough
surface from saw cat are employed. They are usually cut square (plain
edges), and are tongued and grooved for good quality work. The roof joists
generally bridge the shortest span and the boarding is nailed at right angles
to them, although the boarding or its grain should preferably follow the fall
to avoid warping boards retarding flow of water. Each board should be
nailed with two nails to each joist with the nail heads well punched down
below the surface of the boarding. As these boards may shrink and twist
out of level as they dry, chipboard maybe used so as to maintain a level
roof deck. Since a timber flat roof provides poor insulation against loss or
gain of heat, some materials may be built into or onto the roof to improve its
insulation against transfer of heat. Insulating materials are manufactured in
the form of Boards (glass or mineral fibre, PVC, polystyrene foam), slabs
(wood roof), Quilts (glass or mineral fibre), dry fill (expanded polystyrene,
glass or granules of lightweight mineral). When there materials are used
with timber roofs, the boards and slabs are fixed on joists under the
boarding quilted materials are laid between or over the joists and dry fill
between the joists.
Reinforced Concrete Roofs
Construction of these type of roofs is also similar to that of r.c. upper floors,
only that the loads on roofs are less than those of floors and thickness of a
concrete roof will usually be less than that of a floor of similar span. The
constructional concrete topping of concrete roof is normally finished off
level. The slight slope or fall is achieved with a severed of cement and
sand, and with the top surface of the screed finished to the fall required.
The least thickness of the screed being from 20 to 25, concrete roof slabs
are often reinforced with steel bars in both directions, with the larger bars
following the span, which is least width between the external wall or
external walls and internal load bearing walls same way as r.c floors.
To attain thermal insulation, a good thermal insulation material should be
incorporated in the construction of the roof or a lightweight concrete slab
construction be used. This could be done by using lightweight aggregate
for the screed instead of sand. The lightweight aggregate in common use
are foamed slag, fumice and vermiculite.
These three minerals are all
porous, and it is the air trapped in the minute pores of the materials which
makes then lightweight and good thermal insulators. These insulation
boards are most conveniently placed on top of the concrete roof, under the
roof covering.
FLAT ROOF COVERING
There are basically three kinds of material used as coverings for flat roofs,
mastic asphalt, built-up bitumen felt, and non-ferrous sheet metals (lead,
copper zinc, and aluminum).
Mastic Asphalt
Asphalt is a mixture of soft material with low melting point, occurring
naturally and has properties for preventing water penetration. Natural rock
asphalt is hard and chocolate brown in colour. Solid blocks of
manufactured asphalt are heated on site and spread hot over the surface of
the roof in two layers to a finishing thickness of 20 with joists staggered at
least 150mm at laps. As it cools the asphalt forms a continuous, hard water
proof surface. An insulation membrane such as glass fibre may be placed
above the concrete deck and below the asphalt.
Asphalt skirting at upstands should be 13mm thick in two coats to a
minimum height of 150mm above finished level of the asphalt it flat. The
top edge of the skirting should be tucked into the parapet and pointed in
cement mortar. If there is no parapet wall, the roof overhangs the external
walls and the asphalt drains to a gutter.
Coping
Top of
asphalt
skirting
turned into
groove on
Internal
brick
work
angle
fillet
Internal
angle fillet
DPC
Parapet
DPC
50 asphalt skirting
SKIRTING
DETAILS
Insulation
Sheathing felt
Reinforced concrete
Screed
Asphalt in two layers to 20mm thickness
Asphalt finished
over lead strip
nailed roof
Asphalt dressed
over half-round
wood roll
Asphalt apron
Strip of lead sheet
welted and nailed to
boards.
Asphalt in two coats
finished to 20mm
thickness
Fascia
Asphalt
Felt
Boards
Soffit
Cavity
wall
Insulation
Rough
boards
Firing
piece
Joist
Joist
Fascia
Sheathing felt
Hall round
gutter
Built-Up Bitumen Felt Roofing
This roof covering is built-up in three layers of bitumen roof felt. Based
materials such as fibre, asbestos and glass fibre are felted and
impregnated with bitumen for bitumen roofing. The asbestos and glass
fibre based felts have good stability resistance to fire and rot, and used for
good quality roofing work.
The cheaper fibre based felts have low
dimensional stability and are used for low cost roofing work. The felt is laid
across the roof with 50 side lap and 75 end lap between sheets, and with a
shallow fall for rainwater runoff.
On timber board or chipboard roof surface with insulation under the boards,
the first under layer of felt is nailed across and along the laps of sheets.
The second under layer is then bonded to the first in hot bitumen spread by
brush or mop, and similar for the top or third layer to the second layer. The
three layers may all be glass fibre base, or all asbestos fibre base, or
alternated.
On concrete screed finish which may absorb rainwater it is likely for water
to be trapped in the screed under the roofing felt covering, which causes
blisters from the effect of sun. to avoid this, a venting layer of felt on wet
screed roof is used. This perforated layer of felt is laid dry on the screed
and the three layers of felt are then bonded to it. The venting layer allows
water vapour to be released through vapour pressure releases at
abutments and vergers of the roof.
In parapet walls and abutments, the felt is turned up 150 against the
parapet and abutting walls, over an angle fillet, and either a dpc is turned
down over the upstand of the felt roofing or a separate flashing stressed
over the upstand to visit rainwater penetration.
Along eaves and verges, the bitumen felt roofing maybe dressed over
gutters with a welt or a separate non-ferrous drip may be used.
Angle fillet
Coping
Three layers of
roofing felt
DPC
Bitumen felt DPC
Firing pieces
Joist
3 layers of roofing
felt on boards
Gutter
Timber boards on insulation board
Built-up
felt roofing
min
150
Gutter
Fascia
WALL GUTTER
Joist
Wood fillet
Verge board
Gavity
VERGE DETAIL
Sheathing felt
built-up felt
roofing
Fascia
2 coat angle
fillet
Screed
Concrete
CONCRETE ROOF SLAB
Plasterboard
Welted apron
Batten
Gutter on bracket
Fascia
METAL DRIP TO VERGE
Metal
drip
Railing
strip
WELTED APRON TO EAVES
Sheet Metal Roof Coverings
Sheet metal roof coverings have good protection against wind and rain.
They are light and durable. Four metals in sheet form are used; head,
copper, zinc and aluminum. Their properties are as follows:
Lead: - is ductile, flexible and a very heavy metal, used in thick sheets as
roof covering.
It is malleable and can be easily bent and beaten into
shapes without damage. Lead is resistant to corrosion, when exposed to
the atmosphere a film of carbonate of lead oxide forms on the surface of
the sheets and prevent further corrosion. It is non-absorbent and has a
long life span.
Copper: - Is a heavy metal with good mechanical strength, it is malleable
and can be used in thin sheet as roof covering. It can be beaten and bent
into shapes. On exposure to atmosphere a thin coat of copper oxide forms
on the sheets which prevents further oxidation of copper below it, which
makes it resistant to most normal weathering agents (corrosion). It is also
non-absorbent and has a long life span as lead.
Zinc: - This is a lighter metal with good strength, it is not so malleable as
lead and copper. It can be bent in sheet form, but it tend to become brittle
and break. On exposure to atmosphere a film of zinc oxide forms on the
surface of the sheets, and this gradually corrodes the zinc to reduce it’s life
span to between 20 to 40 years. Zinc is also liable to damage in heavily
polluted industrial atmosphere. Zinc is normally used for its less cost.
Aluminum: - One of the lightest metals with average mechanical strength
and is malleable. It is resistant to all weathering agents (corrosion). On
exposure to the atmosphere a film of aluminum oxide forms and prevents
further corrosion. Aluminum as roof coverings has useful life span between
zinc and lead.
Sizes and jointing of sheets
Sizes of metal sheets used for roof covering is determined by the sizes of
sheets manufactured are the need to allow for contraction and expansion of
the sheet. Commonly manufactured sizes are:- lead: rolls 2.4 wide x 12.0
long x thickness in menof 1.8, 2.24, 2.5,3.15 or 3.55.
Copper:
Sheets 1.2 x 600 x 0.6m and 1.8 x 900 x 0.6mm
Zinc:
Sheets 2.4 x 900 x 1 or 0.8mm
Aluminum:
Sheets 1.8 x 600 x 0.7mm, 1.8 x 900 x 0.7mm, 1.8 x 1.2 x
0.7mm.
Some types of joint have been developed which successfully joint sheets,
keep out water and allow the sheets to expand and contract without
tearing. The joint along or longitudinal to the fall are usually in the form of a
roll. Rounded timber battens some 50 square are waited to the roof and
edges of the sheets are either overlapped or covered at these timber rolls.
The joints across or transverse to the fall of the roof are formed as a small
step called a drip. The purpose of the drip is to accelerate the flow of
rainwater running down the shallow slope of the roof. Where there is a
parapet wall around the roof or where the roof is built-up against a wall,
sheets are turned up against the wall about 150 as an upstand. The tops of
these upstands are not fixed to allow for expansion without restraint. To
cover the gab between the upstand and the wall, strips of sheet are tucked
into a horizontal brick joint, wedged in place and dressed down over the
upstand as an apron flashing. Clips are then used to secure the apron to
the upstand to prevent wind from blowing the apron away.
Lead Sheeting: - to allow the metal to contract without tearing away from
the fixing and to prevent the sheet from creeping down the roof, no sheet of
lead should be larger than 1.6m2. A lead flat joints across the fall of the roof
are made in the form of drips or step down, and to reduce excessive
increases in the thickness of the roof due to these drips they are spaced up
to between 2.30 to 2.50m apart and rolls (joint longitudinal to fall) up to
between 675 to 800m apart determined by the width of sheets.
PITCHED ROOF COVERING MATERIALS
Pitched roof covering materials are usually placed and fixed to the already
constructed pitched roof framework of timber or steel. The type of pitched
roof covering material sometimes determines the minimum amount of slope
they are to be laid.
Plain or double lap tiles: - Are made in a wide range of colours, either in
clay or concrete. They are 265 x 165 x 12mm in size, under-eaves and
top-course tiles are each 190mm long and tile-and-a-half tiles for use at
verges are 250mm wide. They are slightly cambered and sometimes cross
cambered in their lengths, so that the tails bed lightly, and to prevent entry
of water by capillary action and to ventilate the underside of the tiles to
enhance drying out after rain respectively. Each tile ha ribs for hanging
over battens and two holes for nails near its head. They are nailed with
38mm nails of aluminum, copper, in zinc at every 4th course and at eaves,
top courses and verges. Untearable sarking felt is provided under the tiling
battens to prevent driving rain from penetrating the roof plain tiles are
constructed with minimum slope of 400.
Gauge
38 x 19 battens Rafter
Lap
Margin
Plain tiles
Rafter
Quilt or loose insulation
Under caves tiles
100 age gutter
25 fascia
Underlay carried into gutter
The lap is the amount by which the tails of tiles in one course overlap the
heads of tiles in the next course but one below, and should not be less the
65mm. Gauge is the distance between centres of battens, calculated by the
formula: gauge = length of tiles minus lap  2, hence the gauge of plain
tiles to a 65mm lap = (265 – 65)  2 = 100mm. The margin is the exposed
area of each tile on the roof and the length of the margin is the same as the
gauge.
38 x 19
battens
Tiler-and-ahalf tile
Half round
ridge tile
38 x 19
batten
Cement mortar
bedding
Felt
underlay
Rafters
Cement mortar
Ridge
board
Main tile under cloak
A typical verge detail above illustrate using tile-and-a-half tile to maintain
the bond bedded on and pointed in cement mortar on an under cloak of
plain tiles. The tiles overhang the wall by 50 to 75mm to give protection
against weather. Half-round tiles bedded in cement mortar are commonly
used to cover ridges. Hips maybe covered in a variety of ways similar to
those used at ridges, this includes: Half round hip, bonnet hip and angular
hip tiles. Examples of valley coverings include; purpose made valley, swept
valley and laced valley.
Purpose-made
valley tiles
Hip iron screwed to
hop rafter
Plain Tiles
PURPOSE-MADE
VALLEY
Tile-and-ahalf tiles
ANGULAR HIP
HALF ROUND HIP
SWEPT VALLEY
Valley
rafter
225 x 25
valley board
Mortar
Tile cut to
required swept
BONNET HIPS
LACED VALLEY
Single-lap tiles: - In single lap tiling each tile overlaps the edges or head
of the tile in the course below and there is also side lap. The overlap
prevents water entering the roof between adjacent tiles, and in
emsequence the tiles can be laid with single and lap. Thus there is only
one thickness of tile on the greater part of the roof with two thicknesses as
the ends and sides of each tile. Dimensions for these type of tiles are
usually fixed by the design of the tile. Some common types of single, lap
tiles are: Italian tiles, Spanish tiles, double ronan tiles, and pantiles. There
are also many forms of interlocking tiles manufactured in concrete. The
principal advantages single-lap tiles over plain tiles is that they give a
lighter roof covering and permit a flatter slope of roofs. They however more
difficult to replace, and not so adaptable to complicated designs. They are
constructed with a minimum slope of 300.
25 x 75 battens
Over tiles
Under tiles
Rafters
Boards
SECTIONM THROUGH ITALIAN TILES
50 x 75 battens
Over tiles
Under tiles
Rafters
Boards
SPANISH TILES
38 side lap
DOUBLE ROMAN TILES
Half round ridge tile
420 x 330mm pantiles
Lap
25 x 50 batten felt
underlay
Batten course bedded
and pointed
WEEK 14
SLATES
Although slates have been superseded by clay or concrete tiles and other
forms of roofing materials, they are still used in slate-producing districts.
Their sizes vary form 255 x 150mm to 610 x 355mm. Each slate is secured
by two nails, at the head or centre of the slate, and the nails maybe yellow
metal, copper, aluminum alloy, or zinc and the vary in length from 32 to
63mm according to the weight of slate. It is customary to centre nail all but
the smallest slates as there is a tendency for the larger head-nailed slates
to lift in high winds. The main advantage claimed for head-nailed slates is
that there are two thicknesses of slate covering the nails, but this involves
the use of a larger number of slates and they are not so easily repaired.
Nails should not be less than 30mm from the edges and 25mm from the
heads of slates.
2.50mm lead
38 x 19 batten
Gauge
Lap
200
Felt
OPEN METAL
underlay
VALLEY
Nails
19 Boarding
2.50mm lead
State-and-aValley rafter 50 x 275
Boarding
covering to
half slate
ridge rill
Verge
50 diameter
LEAD COVERED
wood rill
RIDGE
Margin
Eaves
Side lap
CENTRE NAILING SLATING
Lap Gauge Rafter
Slates Margin
Felt
underlay
Half-round
gutter
Insulation
25 fascia
Ridge
board
Felt
underlay
50 wide lead ticks
@ 750 centres
Angle ridge tile
bedded in mortar
ANGLE RIDGE TILE
EAVES DETAILS
19 soffit
boarding
Slates
Asbestos Cement Slates: - are manufactured in sizes the width of which
is half their length. They are laid with a 75mm lap with a minimum slope of
350. Asbestos cement slates are centre nailed with two copper wire nails to
each slates, and the tails are prevented from lifting by a copper rivet
passing the tail and between the edges of the two slates of the course
below. The slates are so light that the rafters can be spaced up to 750mm
apart. Two under courses are required at caves; slate of slate-and-a-half
width are used at verges; asbestos cement ridge and hip coverings are
available in addition to clay and cement fittings, and open metal valleys are
preferable.
Lead cup washer
Asbestos washer
100 x 6 galvanized
Driving screw
Asbestos washer
8 diameter
galvanized hock
bolt
Lead cup washer
Timber purlin
FIXING ASBESTOS CEMENT
SHEETING TO WOOD
Asbestos Cement Sheet
PURLINS
HOCK BOLT
Packing piece
Glass fibre insulation 25
thick
Asbestos Cement living Sheets to 75 head lap
FIXING ASBESTOS CEMENT SHEETING TO STEEL PURLINS
2 piece ridge
capping
Asbestos Cement Sheets
Steel purlins
ASBESTOS CEMENT RIDGE CAPPING
SHEET COVERINGS TO PITCHED ROOFS
Sheet coverings are available in different materials are particularly well
suited for garages, stores, agricultural and industrial buildings.
One of
these common material is asbestos cement which has a natural grey
colour. sheets are normally corrugated about 50mm deep in various
lengths up to 4.60m. They are laid with an end lap of 150mm and the side
lap varies with the design. Asbestos cement sheets are fixed to wood
purlins with galvanized drive screws or to steel-angel purlins with hook
bolts. The bolts or hooks should be placed on top of corrugations and lead
cup washers to form a watertight joint. Special fittings are made for use at
ridges, hips, corners and eaves. The sheeting is unattractive and although
it is incombustible and light in weight, the surface softens with wreathing
and becomes brittle with age and hardly attain a life span of 30 years.
To counter this brittleness other materials have been produced, such as
incorporating a core of corrugated steel covered with layers of asbestos
and bitumen. This combines the strength of steel with the corrosionresisting properties of asbestos.
Corrugated galvanized steel is inclined to be fairly short-lived, nosy, subject
to condensation and rusting at bolt-holes, and is not well suited for most
purposes. Aluminum sheets are also useful for roofing purposes. They are
corrosion resistant, of light weight and have good appearance, their
reflective value has some thermal insulation properties. The minimum
recommended slope is 150 and the sheets are fixed in a similar manner to
other corrugated sheet materials.
The edges of sheets longitudinal to the fall are lapped over a timber which
is cut from lengths of timber 50squares to form a wood roll. Two edges of
the batten are rounded and two sides slightly splayed so that the soft metal
can be dressed over it and the waist so formed allows the sheet to be
clenched over the roll, without damage.
To provide a smooth surface for sheet lead to contract and expand, an
underlay of bitumen impregnated felt or water proof building paper is first
laid across the whole roof boarding before the rolls are nailed. The edges
of adjacent sheets are dressed over the wood roll in turn. The edge of the
sheet is first dressed over as underlay or under-cloak and is nailed with
copper nails to the side of the roll.
The edge of the sheet is then dressed over as overlap or over-cloak with a
40mm opposite splash lap, without nailing to allow for contraction. Drips 50
deep are formed in the boarded roof by nailing a 50 x 25 fir batten with an
anti-capillary groove and a rebate (into which the underlap is dressed and
nailed) between the roof boards of the higher and lower bays. The groove
ensures that no water rises between the sheets by capillary action. At
abutments the lead sheet is turned up the wall face 150 as an upstand and
150 apron flashing passes over the top of the upstand to form a watertight
joint. The top edge of the cover flashing is tucked and wedged into a brick
joint and lead tack or clip prevent the edge of flashing from curling.
Rainwater discharges into a parallel 300 deep lead gutter, constructed to
slope or fall towards one or more rainwater outlet of pipe or pipes. These
can be fixed outside or inside the building. When the rainwater pipe runs
inside the building, it is usual to form a cesspool or eatchifit at the and of
the gutter to act as a reservoir against flooding during hearing storm.
Bossed end of roll
Sheet lead dressed
over roll as overlap
Sheet lead
dressed as
overlap
at drip
Felt
Sheet lead dressed
as overlap
Felt
Underlap
Felt
50 drip
50 x 50
woodroll
Sheet lead dressed
as underlap
Batten
with anti
capillary
groove
Roof
boards
Boarding
Edge rounded
50
Felt under
lead
Lead tacks
50
Lead wedge to
apron at 450 dc.
Sides wasted
Apron
Cement/sand
fillet
40 wide lead
tacks at 750
c/c
Lead apron
Upstands
Felt
Boards
Insulating
50 drip
Joist
Upstands
Sheet lead
Fall
Roll
Felt
Boards
Insulating boards
Apron
Sheet lead on felt underlay
Roll
Fall
Bossed end
Lead dressed
over fascia
into gutter
Fall round
gutter
Wall out
away to show
Roll
cesspool
Sheet lead
Brick
wall
Firing piece
Joist
Upstands
Lead pipe
Fascia
board
Cesspool
COPPER SHEETING: - Copper sheeting in a few years becomes covered
with a light green compound of copper called patina, this gives the sheets
pleasing colour and texture. The patina is black in heavily polluted areas.
There are two sort of joints used for rolls in copper sheeting; the batten roll
and the conical roll. (a) Batten rolls are splay sided timber batten fixed to
the roof at 750 centres with brass screws, the heads of which are counter
sunk into the batten. The edges of the sheet are turned up each side of the
batten and a separate strip of copper sheet is then welted to the roof
sheets as a capping. The sheets are secured by means of 50 wide strips of
copper cleats fixed under the rolls at 450 apart and folded in with the
sheets and capping. (b) Alternatively the edges of the sheets can be folded
together in the form of a double welt over a conical section roll at 750
centres. Less sheet is required to form the conical roll the batten roll joint.
Since drips formed in roof covers are spared up to 3.0 apart and copper
sheets are either 1.2 or 1.8 long a double lock welt’ joint transverse to the
fall has to be used, and because the joint is across the fall it is called a
double lock cross welt.
The double lock cross welt is folded up with the sheet at rolls and they are
staggered to avoid welting too many thickness of copper sheets. Drips are
the formed in the timber roof with a 63 or 70 step down using a batten, and
the edges of the sheets are welted. Where the roof is surrounded by a
parapet wall the provision and arrangement of upstand, apron and box
gutter is exactly the same way as that formed for a lead covered roof, with
cesspool for flood collection before discharging through pipes. Where there
is no parapet wall around the roof and attractive eaves gutter is provided.
Edges or verges of the roof down to the fall are usually finished with a roll
copper chips.
Upstand
Apron
Copper
Sheets
capping
welt
Apron
Saddle piece
Saddle welted to
capping
Copper
sheets welted
over roll
Batten
roll
50 wide cleat
at 450c/c
Felt
Underlay
0.6mm
copper sheet
63 x 50 conical
wood roll
Underlay
Underlay
Cleats
Copper
sheet
Double lock
cross welt
folding in at roll
Upstand ent to
shape of roll
and welted
Conical roll
Copper sheet
Fall
Board
Welt
Batten
Fall
Firing piece
16
Double lock
cross welt
Cappeing
End of roll is
splayed and
upstand trimed and
Batten roll
belted to shape
Copper
Down
sheet
dressed
Felt
into gutter
Fall round
gutter
Copper sheet
Boards
Fascia
Soffit board
Apron welted to
sheet dressed
over batten and
down fascia
Fascia
Joist
Eaves
Welt
Batten roll
40 wide clips
nailed to fascia
at 450 c/c
Zinc sheeting: - Joints between sheets are designed to avoid much folding
of the stiff metal. The joints along the fall are formed over a wood batten.
The sheets are bent up on either side of the batten and are secured by
means of 40 wide sheet zinc clips nailed under the batten at 750 centres,
and the clips are turned up and clipped over the edge of the sheets. The
batten, bent-up and clips are then covered with a 1.35 length of zinc
copping secured by means of a holding down clip which is folded act of a
strip of a zinc sheet. The holding down clip is nailed to the batten over the
end of the capping, the end of the next length of capping is inserted into the
fold in the holding down clip and then placed on the batten and in turn
secured with a holding down clip. The battens are usually at 850 centres.
Where there is no parapet wall around the roof the sheets are turned up
against it 150 as an upstand and covered with an apron flashing tucked into
a joint in the brick wall. The roof then drains to a zinc lined box gutter. If
there is no parapet wall the sheets drain directly onto an eaves gutter.
40 wude clip
nailed under
rols at 750c/c
Lower edges
of capping
feinted to grip
sheets
Holding down clip nailed
batten over the end of
cappng with the next length
of capping tucked to fold.
Zinc
capping
Capping
Upstand
Zinc sheet
Nail
Underlay
Batten
roll
Zinc sheet
Batten
Boards
Clip turned
over upstand
of sheet
End of capping
splayed and
flattened and
dressed over
drip.
Felt
underlay
End of capping
folded and
flattened at
upstand
Zinc Aprove
Batten
roll
Capping
Walted drip
Capping
Felt
Boards
Edge
beaded
Batten
Batten
roll
Roll
Upstand
Firring piece
Zinc sheet
BEADED
DRIP
End of roll splayed
and flattened and
dressed over
drip.
Half round
gutter
Batten roll
Zinc sheet
Boards
Clips at 750 c/c
Fascia
Beaded
Drip
Aluminum sheeting: - The thickness strength and malleability of
aluminum sheet is comparable to that of copper sheet and it is jointed and
fixed to the roof in the same way as copper sheet wife either batten or
conical roll joints along the fall and double lock cross welts and drips across
the fall, the details of these joints shown for copper sheeting apply equally
for aluminum sheeting.
SHEET METAL COVERING TO CONCRETE ROOFS
Bitumen felt and asphalt have been used as covering to concrete flat roofs
simply because of their cheap cost and the ease of laying them. But they
have only a lifespan of 20 years. One of the sheet metals in sometimes
used instead. The sheet metal is jointed and fixed to a concrete tool in the
same way as on a timber roof. The wood rolls are secured to the concrete
by screwing them to splayed timber battens set into the screed on the
concrete or by securing them with bolts set in sand and cement holes
punched in the screed. Drips should be formed in the surfaces of the roof
as in timber roof, and details of jointing and dressing of the sheets is the
same as those shown for timber roofs.
WEEK 15
SUSPENDED CIELINGS SYSTEM
A suspended ceiling is employed in may modern buildings to provide
a smooth level ceiling without regard to the structural form of the
building.
The ceiling can be use together with the cavity between it and the
structure, for various purposes.
1. Service pipes for water, electricity and drainage can be concealed,
although they are still on the surface and therefore accessible.
2. Air-conditioning can be accommodated in the space.
3. The space itself can be used as a means if circulation of air
(plenum).
4. The ceiling can be use to accommodate light fittings. These can
be flush with the ceiling with all but the diffuser concealed.
5. the ceiling material can be selected so as to provide sound
absorption where this is required by conditions in the room.
Two types of suspension are used:
Exposed tee: the bottom flange of the tee supporting the tiles is
visible and tiles rest on it
Concealed tee: the tiles are grooved (kerfed) to fit over the , thus
concealing it.
The remainder of the suspension consist of main rails, at about
1200mm centres, supported by hangers which are fixed to the
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construction. The tees are fixed to the main rails at the tile spacing,
usually 300 or 600 mm, with noggin pieces between the tees at a
similar spacing.
A cathedral ceiling is any tall ceiling area similar to those in a church.
A dropped ceiling is one in which the finished surface is constructed anywhere
from a few inches to several feet below the structure above it. This may be done
for aesthetic purposes, such as achieving a desirable ceiling height; or practical
purposes such as providing a space for HVAC or piping. An inverse of this would
be a raised floor.
A concave or barrel shaped ceiling is curved or rounded, usually for visual or
acoustical value, while a coffered ceiling is divided into a grid of recessed square
or octagonal panels, also called a lacunar ceiling.
A cove ceiling uses a curved plaster transition between wall and ceiling; it is
named for cove molding, a molding with a concave curve.
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Ceilings have frequently been decorated with fresco painting, mosaic tiles and
other surface treatments. While hard to execute (at least in situ) a decorated
ceiling has the advantage that it is largely protected from damage by fingers and
dust. In the past, however, this was more than compensated for by the damage
from smoke from candles or a fireplace. Many historic buildings have celebrated
ceilings, perhaps the most famous is the Sistine Chapel ceiling by Michelangelo.
The ceiling of Wells Cathedral, England.
Stretched ceiling
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