Chapter 7: The building site, site clearance and setting out

Objectives They usually accept land allocated to them by the Local Authorities
Where a choice has to be made, the following factors are considered.
By the end of this chapter you should be able to: 1. Services and facilities
1. define a building site;
2state and describe factors considered when choosing a site: People want to stay where they get commercial and social servicas.
The services and facilities expected are schools, shops, transport, social
3. identify and explain items considered during the site investigation;
amenities, water supply, and electricity, among other things.
4. define site clearance and suggest why the vegetable soil is removed from
the area enclosed by the external walls of a building: 2. Type of soil
5. state other materials removed from the site before construction. The type of soil helps people decide where to place a building or locate
residential areas. Foundations need firm and stable ground while top
soil may be needed for growing crops.
The building site and site clearance 3. Climate

Introduction The amount of rainfall, temperatures and periods of sunshine for a

particular area will determine and influence the design of the building.
Besides, the design, location of a building and the general demand for
After a client has been allocated land to build on by the local authority, land are also dependant on the factor of climate. People choose areas
the landowner should seek an architect to draw plans for him for work where temperatures are favourable.
intended to be put up. The plans or working drawings are sent for
approval by the local authority. Usually land given for the construction 4. Terrain of the ground
ofabuilding is already surveyed and serviced. Where the building site
has not been serviced it must be investigated. Asite for construction of, This is also a fairly important factor to be considered when determining
ahouse or building is called the building site. It is a stand or surveyed selection of abuilding site. A flat site is easier to work on, while a
plece of land upon which abuilding is being constructed or is to be sloppy ground will make excavations for trenches and backfilling more
Constructed. expensive. Marshy,filled up ground and low level sites are a problem
during the rain season. They may become water-logged and this could
cause health and sanitary problems.
Choice of a site 5. Use of the building now and in future
The choice of a building site depends on many factors. In towns, it
mainly depends on the availability of land either for domestic use or Use of a building will place the building on a suitable and appropriate
choice. position. A company building where manufacturing takes place, and
industrialor commercial purposes. People no longer have much
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 under the
where smoke and water wastes reouire disposal will be placed or that underground installationsproblerns if building are not
iteo
away from residential areas This is why you find industrial sites out
tOwn away from houses A church on the other hand is sited near where
Or as they are likely to
sewer and water pipes
cause
will be difficult to repair if reonrerdes
repairsS are to te
fitted urder tre
peope reside and usually in a quiet place Where a building will need building
to be altered, changed improved or additions made, choice of the site
should be consdered to make this possible. Size of the site should be 3. Soil tests
sUch that the changes can be made with minimum problems. Samples of soil from the site and from the trial pits are tare tcr
laboratory tests to determine suitability for building The tests
Site investigation to help the designer or engineer decide on the type of fourdaticr arerer
emoloved. Also the tests willverify the bearing capacity of the scl re
Site nvestigaton is done on new sites where big or major building investigated.
projects are to be undertaken This is not done on serviced stands
t s a requirement by the local authonty that sites for major building
OPeratons be investigated and to to take note of soil conditions which 4. Proximity to existing properties
will afet the foundations to be used The investigation of the site will Where an excavation is liable to cause consequental camace r
Ivohe the soil conditon study to detemine the ability of the subsoil adjoining buildings, structures or property, the adjacent tuiicircs ue
to recene the load from the foundation. Type of terrain, topography. be supported. Underpinning can be carried out to stog the zicrre
obstructons. subsoil installations and/or the closeness to other already buildings from collapsing, moving or damage Underpineirg s te
exStingproperties are some of the investigative activities carried out.
Support given to an existing building's foundations or base to prevant
it from moving or collapsing when its adjoining site is being ug and
1. Soil investigation excavated.

Investigation of the soil will include carrying out soil tests, studying soil
profies Cigg1ng tnal prts and trial holes Trial pits will show to what
Advantages of site investigation
extent thesod can release water and what water content it carries, while Itis important that site investigations be done for a numter ci ressons
rial hoies shoOw the same and aliow samples of soilto be taken for tests The contractor is saved from legal action by the locai autorty T
to be condUcted on it in order to determine its suitability for building. owners of the adjacent properties
This also aliows for the soil profile to be studied. Pits or holes are dug () The designerlengineer is furnished with enough informator alcu
t0 at eest one mete or more him to proceed with informed decisions as regards iourtaners
size and type of building to be constructed
2. Subsoil installations (i) Forewarned is forearmed. The client and the contractor ae co
made aware of the problems to be expected during the cçeratos
Underoroung installatbons can be water pipes, Sewer pipes or electrical The warning will therefore enable them to take approoate ses
cabies These need to be sdent1fied to avert poss1ble accidents or danger and plan in advance to solve the problems before as a
to worKmen and machinery working on the site. Water pipes or sewer OCCurs.
prevent
ppes can be intertered with or can be broken when digging trenches (iv) Proper and careful planning of operations is put n place to
and other excavavons ldentification of these before work starts willcut unnecessary danger to workman, damage to pipes, cables or
on unnecessary repaif CoS1s that may be incurred You will appreciate pylons and even machinery.

50
Site clearance Cut x level X retainng
wal
fill y
According to the model building by-laws Chapter 2 Section 25, 'No
person shall erect a building upon ground upon which there is any
vegetable matter or any offensive or unhealthy waste, substance or
-Cut 'x' is made to fil| 'y' so that the
matter, or any substance liable to disintegrate or decompose, unless buildingsite level is now the reduced
and until he has had allsuch matter and any earth so rendered unstable level xx. Setting out will take place on
or unhealthy removed from the site, or treated so as to render it stable this level. (NB. x cut, y fill
and healthy' Fig. 7.1 Cut and fill method
Also during site clearance, old buildings can be demolished, the
debris cleared away and existing services disconnected and removed. contractor to be able to do this, he will have to do the task of interpreing
Virgin sites have to be cleared of grass, leaves, trees and rocks. Roots the design provided by the architect. If setting out is badly done.
tie
oftrees should be properly removed to ensure that they do not cause resultant building will be wrong and this may prove to be costiy for ihe
stnuctural damage to floors. The local authority can be asked to grant contractor to make corrections.
permission to leave standing any tree, bush, plant or lawn which should
be specified by the owner of the site.
It is important to dig out top soil to a reduced level or minimum Setting out tools
depth of 150mm. Top soil can be kept for use for lawns or areas to be The tools that you require for this job will include tape easures or a
seeded when the building work has been completed. The reason why
topsoil or the vegetable soil is removed is to prevent anyplant life growth tape measure, bricklayer's lines, club hammer, claw hamer, bulder s
underneath the floors of the building. Sometimes the decomposed square, the spirit level, profiles,nails, cross cut saw,among other things
vegetable matter will create a space/vacuum under the floors hence These are only basic tools. On larger or bigger projects equipmeni Ek
cause the floors to collapse.
the site square, dumpy levels and theodolites are necessary
Site clearance is not complete until the site has been levelled. High
portions are cut to fill up lower portions. This is called the cut and fill Correct setting out procedure
method (Fig. 7.1).
Closer attention should be given to weak soils where it may be When you start setting out make sure that you observe the following
necessary to import stronger earth to replace the weak soils on your steps:
site. This includes the use of termite chemical fumigants to control 1. Identify the local building line. This reference line willmari the outer
termites on the site. Ant hills should be dug out and be replaced with face of the front wall of the structure to be built. The line ensures
better imports of earth. that the building faces the right direction and that the buiiding is a
certain distance from the road or other buildings.
2. The building is located and will be erected on the correct site or
Setting out 3.
stand. Ensure this i_ the correct position.
The overall length and breadth sizes of the building must be
g Out is a process carried out by a contractor to mark out the according to those shown on the working drawings.
nutines of a proposed buildingon the ground. The shape of the building 4. Establish adatum level. This level is a reference point from which
Pall is set out on the around after the site has been cleared. For the all other levels of elements of work may be taken when working.

51
 ror example, oepth of foundations. DPC levels, wall plate heign length t building
ee mesSUred from this basic leve! The datum level or peg Is
piaceð on the highest point on the site and 150mm above ground
(Fig 7.2). A building line

6m Ern
distance from
datum peg Ibuildingposition road center
peg
proposed of
150
belowtop Fig. 7.3a) Establishing the building line
2. On pointAand B mark or set 90° cormers of theidire s- ..
direction with a tape measure in the ratio 3m:4m:5m.
this
sloppingin
site
-rarirg ires
atleast
2maway
Sm
timber guards 5m
4m
Fig. 7.2 Position of the datun peg peg peg
A
3m

peg
Methods of setting out rectangular buildings peg

There are two methods of setting out simple rectangular buildings. The Fig. 7.3b) Marking 90° corners of the building
methods are the 3:4:5 method and the builder's square method.
3. Mark the width of the building at C and D and recet re
The 3:4:5 method of setting out procedure as at A and B (Fig 7.3c).
This method uses the concept of a right-angied triangle with sides in the
D 4m C
ratio 3:45. The sides of ratio 3and 4 meet at an angle of 90° which is 4m

Usedto corme up with the 90° corners of the rectangular building being tape measure
5m
set out Larger dimensions in the same ratio can be used, for example, 3m
6:8:10, 15.2025 or 3040:50 etc.
Sm
Procedure for setting out with the 3:4:5 method 4m 20m

1. Establish and work out the building ine from the road or existing 3m
A
buidings. This line already forms the front of the building being set out
(Fig 7.3a). On the ine mark the length of the building A and B Fig. 7.3c) Marking the width of the building

52
 The angles DAB, ABG, BD and CbAshould be 90
Check the diagonals DB and AC. These must be equal if the
nrocess above is done accurately (Fig. 7.3d). If DB and AC are not
equal, repeat the procesS once more. Am
3n 5m
ranging res
peg fored an profles
D
3m Sm
peg
Am

side profile
10m

Fig. 7.3f) Setting partition walls by the 3:4:5 method

A 20m 7 The lines of excavation for the foundation trenches are marked on
these profiles (Fig 7.3g) and later marked or transferred ontT the
ground.
Fig. 7.3d) Checking the diagonals for accuracy

5. Corner profiles can be erected on which ranging lines from the

pegs are transferred (Fig. 7.3e).

position of wal
width of trench
side profle
10m corner profiles
corner profile

peg. 20m Fig. 7.3g) Marking the lines of excavation

Profiles
ig. 7.3e) Corner profiles and ranging lines These are temporary rails used as guides in setting out buikdings. On the
6 profiles are marked the position of walls and the width of the foundation
Partition walls are also set by the 3:4:5 method and their positions trenches. There are twO main types of profiles. These are corner and
are marked on side profiles with either nails or saw cuts (Fig. 7.3f). side profiles (Fig 7.4).

53
 builder's square

Dson of wal
Width trench
wal
p lo s i t i o

rencwidtth
h
trenc
w hidth

building line

Fig. 7.6a) Builder's square along the frontage line

3 Stretch aline from another corner peg so that it is parzlel tr

second side of the builder's square to obtain the first corner f
(Fig. 7.6b).
comer profile
peg
Fig. 7.4 Side and comer profiles builder's square

The builder's square method of setting out peg

This mehod makes use of the large wooden builders' square to set 90°
omers The triangle has one of its angles as 90° (Fig. 7.5). 900
building line
Fig. 7.6b) Obtainingthe first corner of 90°

Repeat this method for all corners after marking out the lengr nd
width of the proposed building. The partitions are also set cut ra
similar way (Fig. 7.6c).
90 corner

Fia. 75 Builders square

Dutcer s

Procedure for setting out with the builder's square

method
Fstablish the build1ng Iine, the front of the building as for the 3:4-5
method above. pegs
Place one of the builders square sides along the frontage line (Eio position walls
7 6a) Fig. 7.6c) Sotting out the partitions

54
 ARer setting out the pegs for all the main
5 corners and partitions of
the building, protiles can be erected to take
walls and trenches in the same way the ranging lines for 2. Template method
3:4:5 method.
described above as for the This méthod will make use of a pre-made circular rigid wooden
Diagonals of the set out rectangular building should be checked to fràmework that determines the intended curve of the circular structure
6.
confirm accuracy of work done. (Fig. 7.8).

-circular edge to mark positon cf wal

Setting out circular work

Circular work, like water tanks and huts among other structures, can be
set out using the trammel or template or the string method. Setting out
circular work is easier and faster than the methods used for rectangular
dotted line (position of wa)
work described above.

Fig. 7.8 Setting out circular work (Template method)

1. Trammel method
In this method of setting out circular work, a concreted peg or strong
steelpeg is driven into the ground on the centre of the proposed circular 3. String method
building to be set. A measured timber piece with adetermined radius
and drilled hole on one end is used to mark the wall and trench widths A string is tied to apeg and stretched in a circular motion to mark the
(Fig. 7.7). wall and trenches as required. A peg is tied on one end to mark the
ground (Fig. 7.9).

string markng peg

on end

width or
fixed peg
position of well
radiusofstructure
timber piece

strongsteel peg
trench width trench width
(foundation)
Fig. 7.7 Setting out circular work (Trammel method) Fig. 7.9 Setting out circular work (String method)

55
 strut wedge
Trench excavations pcirg tGard

Ater sefting out, mark the trench woths on the ground to start digging
i e c dioong can be shelow medum and deep Shallow trenches 1.5rn
O7 1m groun are dug to a minmumn depth of 450mm Medium to
Oeetenches are rather danoerous and therefore need timber suppots
i0 De'eicollapse and the bunal of workmen doing the excavatonS.
Exavation is by hand or use of mechan1calexcavators VWhich tools are
JseI foT diggIng foundations?

Trimming and bottoming of trenches

Fia. 7.11 Open boarding timbering on firm ground and shallcw rerc
Kier i n a trench to the reguired depth, the sides of the trench
mUs be trmmed using a spade The bottom is levelled using the spade Moderately firm soils require open boarded tmbering with cirg scars
an3 atock Lower portions are filed from higher portions of the trench spaced to some 500mm apart (Fig 712).
bese This is calied bottom1ng Soon after bottoming the pegs can be
Diaseg at oonvenieni ntenvais to mark the thickness of the foundation
co70ete Fig 710) Reverse the spirt level as you mark and position 500mm
the pes 500mm 3CIg carcs

concrcte foundation peg

strut

Fig. 7.10 Trinming and bottoning a trench

Fig. 7.12 Open boarding timbering on moderately fin sod
Timbering of trenches deep trenches
deed
ne renco
Trenches on conpst aig fn soils tequne no timbeing it they are On waterlogged sols, where the sol is unstabie and This me2sure
shallow Howevet, 1 fhe teches n1e deep open boarded timbenng is the trench måst be tmbered securely by ciose boarding
disturbances
necessary In this tiritbeting fneftiod 1he poling boatds ate Daced o will ensure the safety of workmen and munimSes
sorme 1.5m apart (fig 711) progress (Fig 7 13)

56
 trench side
After site clearance, seting out of the building begins. This process
poling board calls for the attention of an experienced workmen or expert, for a badiy
done job will be too costly for the contractor. Simple setting out methods
have been discussed in this chapter. However, the reader will find
strut more modern methods in use by big organisations where sophisticated
equipment is used. For bigger projects setting out is a continuous
operation throughout the construction of the building and it affects very
much the progress of the project.
walling board

wedge
Vocabulary
1. Building line -a line established by the local authority to wnich new
Fig. 7.13 Close boarding timbering in loose and waterlogged soils buildings must conform. The line is measured from the cantte of a
The choice of the timbering to be used will largely depend on
road or already existing buildings.
number 2. Building site - a stand or plot or surveyed or limited area of land
of factors namely: the type of soil requiring support, the depth of upon which a building is being constructed.
the trenches, the quality of timber available for use and the time the 3. Cut and fill method used to cut high portions of the site to fl up
timbering will be in use. It must also be remembered that trenches low portions.
must be protected to prevent people from falling in. Wooden fences or 4. Datum peg - a peg established on the buiding site used s a
red ribbons along and round the trenches can be used to warn people point of reference and guide to tradesmen on all the levels to be
before they fall into the trenches. determined on the building. It is placed on the highest point of the
ground at 150mm above that ground.
5 Profile -a temporary wooden rail used as a guide in setting out a
Summary trench for foundation work.
6 Setting out - process of marking out the outlines of a propcsed
We have pointed out that the choice of a site depends on many factors.
However,the choice may be as a result of the availability of land without building structure on the ground and marking out the outines of a
taking into consideration the other factors. wall on a concrete foundation.
7. Site investigation - is a thorough study of the proposed bulding site
Where land or a site has not been serviced, it is essential to carry
Out asite investigation to ensure that specific buildings are built on which involves the soil, type of terrain, topography, obstructons,
Specific pieces of land. Soil tests, trial pits and holes, topography, subsoil installations, proximity to existing properties etc which is
terrain study, subsoil installations and a study of the existing buildings carried out at the design stage.
8 Sub-soil - the ground which receives the load from the foundabon.
among other things will form the basis of the site investigation. Where
the local authority understands the behaviour of certain soils, they may
recommend that no site investigation be carried out in certain areas for Activities
single storey buildings.
Finally, before a building is put up the site must be cleared of Dig at least two pits, 1m deep or more on two different sites. Measure
topsoil to a depth of at least 150mm. Trees, grass, leaves and other each layer of the soil profile and express it as a percentage of the 1metre
debris must also be removed. Clearance is completed by levelling ot dug. Your soil profile should have the layers or some of them: humus,
he site which should include replacement of weak soils by stronger fil. top soil, subsoil, gravel or parent rock. Make your own conclusions of
57