Item 4: foundation excavation; this involve the removal of soil along the path of the building wall as drawn on the architectural plans and structural plans as the case may be. For a simple bungalow, a foundation layout showing the width of excavation ( girth) is used to carry out this operation.

1.width of foundation excavation or trench = to 3 x width of the block to be used for the building
e.g, for a bungalow built with a 150mm ( 6'') on relatively solid soil, width = 3 x 150 = 450mm
for a bungalow built with 225mm (9''), width = 225 x 3 = 675mm

for a poorer soil of low bearing capacity ( water lodged and sandy soil).
width = weight of wall per unit length/ bearing capacity = w/qu (N/m/N/m2)
where the weight of wall per unit length = unit weight of block wall plus finishes x height of wall.

some strip foundation for a bungalow can be reinforced if the soil is poor.

2. Depth of foundation for a simple bungalow ( strip foundation)

Cost of excavation: the rate of excavation is around N1000- N600/m depending on the location of the project.

Bill of quantity is prepared in cubic meters but labourers are paid per meters. you will need to work out the discrepancy.
1 cubic meter of a trench of the following dimensions 675mm x 900mm x 1000mm can be converted into a linear measurement = 0.6075cubic meters will be 0.6m for the perimeter billing.

mix ratio for foundation footing for bungalow should either be 1:3:6 or 1:2:4 for normal soil.
i prefer 1:2:4 ( 1 bag of cement : 4 head pan of sand or 1 wheel barrow of sand : 8 head pan of gravel or 2 wheel barrow of gravel). reason been that the foundation of bungalow is very important because it help to distributes the wall load to foundation adequately.
A typical foundations supporting a three bedroom flat or its equivalent should have the following features

1. minimum thickness of 100mm ( 4'') and should not more than 225mm (9'') thick on a strong soil for economy reason.
2. the sharp sand should not be too smooth and free from clay and other dirt which may reduce the strength of concrete
3. the gravel should be preferably 3/4 ( 20mm) thick and must be free from dust.
4. the water for mixing should be drinkable and free from salt and other chemical contamination
5. the water-cement ratio must not be greater than 0.6.


mode of calculating the volume of concrete for foundation footings ( strip foundation).
1. get the sum of the total gird of the substructure, let say 'P' = 50 ( example)
2. get the width of the foundation, say 450mm (18'') for 150mm ( 6" wall and 675mm ( 27" ) for 225mm (9"wall
3. Assume a thickness of say 150mm for 6" wall and or 225mm for 9" wall.
4. convert all your dimension to 'm'
5. hence volume, v =50x 0.45 x 0.15 = 3.375m3
6. increase the volume by 25% to cater for shrinkage and wastage. =1.25 x 3.375= 4.05m3

using mix ratio 1:2:4
part of cement = 1/7 x4.05 =0.58m3
since the density of ordinary Portland cement s 1506kg/m3
and i bag = 50kg
hence, no of bags = 0.58 x 1506/50 =17.4bags ( 18 bags aprox.)

part of sand = 2/7 x 4.05 =1.16m3
since the density of sharp sand is 1600kg/m3 and a tonne of sharp sand is 1000kg
hence, 1.16 x 1600/1000 = 1.856tonnes ( 2 tonnes aprox.)

part of gravel = 2 x 1.16 = 2.32m3
since the density of gravel is 2400kg/m3 and a tonne of gravel weight 1000kg
hence, 2.32 x 2.4 =5.57tonnes ( 6 tonnes )

part of water using water cement ratio of 0.6
weight of water = 0.6 weight of cement = 0.6 x 18 x 50 =540kg
volume of water required, from density = mass/volume
making volume subject, volume = mass/density
where density of water = 1000kg/m3
hence, volume of water required = 540/1000= 0.54m3
since,1m3 = 1000liters
volume of water required = 540 liters