Estimate of Building Work
It is essential to know the probable construction cost beforehand, called the estimated cost for building construction.
If this cost is higher than the funds available, Work is reduced, or changes are made in the specifications to reduce the cost. By it, you can know the importance of estimate for civil engineers.
For making an estimate, the quantities of different work items are determined with the simple mensuration method, and these quantities help in the cost calculation.
The process of estimation is easy, not rocket science, but you must know drawing.
If you can read or understand the drawing, you may find the dimension length, width, height. Essentially the calculation made of length x width x height/depth or length × height/depth.
You have to take the dimensions (length, width, height, or depth) from drawings(plan elevation and section).
Imagine the building and picture in mind to take the dimension correctly from the drawing study.
There is no fixed rule to determine the dimension from the drawing, but you must have to take measurements accurately.
Special attention is needed at corners, wall junction and wall meeting points.
Usually, foundations are symmetrical, for which the following methods may estimate quantities of different work items such as earthwork in excavation, foundation concrete, foundation brickwork, plinth and brickwork in the superstructure.
Method of Building Estimate
- Long Wall Short Wall Method
- Centre Line Method
Long Wall Short Wall method
The long wall short wall method is the simple method to estimate the quantity of different work items.
You have to determine the external length of the long walls out to out, usually running in a longitudinal direction.
The internal length of short or cross, or partition walls generally runs in the transverse direction. By multiplying this length with the width and height of the wall, you can calculate the quantities.
With the help of these walls length, you can calculate the different work items such as excavation in the foundation, foundation concrete and masonry wall.
But remember, you need to take care while noting the difference in dimensions at different height because of height offset or footing.
You have to imagine the drawing at different heights for convenience, such as foundation trench, foundation concrete, etc. and separately deal with each part.
The simple way to use this method separately consider the long walls and short walls and calculate the centre to centre distance of each wall from the drawing.
For the symmetrical footing on either side, the centerline remains the same for the superstructure and the foundation and plinth.
Estimate of Building Work By Long Wall Short Wall Method
Out to out length of long wall = Centre to Centre length + Half-width of one side + Half-width of another side
= Centre to Centre length + One Width
In to in length of short Wall = Centre to Centre length – One Width
Usually, long wall length decreases from Erath work in excavation to brickwork and the short wall-length increase
From the above image
Centre to Centre Length of Long Wall = Inner Length + Half-width of one side + Half-width of another side
= 6 + 0.15 +0.15
= 6.30 meter
Centre to Centre Length of Short Wall = Inner Length + Half-width of one side + Half-width of another side
= 5 + 0.15 + 0.15
= 5.30 meter
|1.||Earthwork in Excavation|
|Long Wall||2||7.20||0.90||0.90||11.664m||Length = 6.30+0.90 = 7.20m|
|Short Wall||2||4.40||0.90||0.90||7.128||Length = 5.30-0.90 = 4.40m|
|Long Wall||2||7.20||0.90||0.30||3.89||Length is same as above|
|Short Wall||2||4.40||0.90||0.30||2.376||Length is same as above|
|First Footing||2||6.90||0.60||0.30||2.484||Length = 6.30+0.60=6.90m|
|Second Footing||2||6.80||0.50||0.30||2.04||Length = 6.30+0.50=6.80m|
|Plinth||2||6.70||0.40||0.60||3.216||Length = 6.30+0.40=6.70m|
|First Footing||2||4.70||0.60||0.30||1.69||Length = 5.30 – 0.60=4.70m|
|Second Footing||2||4.80||0.50||0.30||1.44||Length = 5.30 – 0.50=4.80m|
|Plinth||2||4.90||0.40||0.60||2.352||Length = 5.30 – 0.40=4.90m|
|Long Wall||2||6.60||0.30||3.20||12.672||Length = 6.30 + 0.30 = 6.60 m|
|Short Wall||2||5.30||0.30||3.20||10.176||Length = 5.30 – 0.30 = 5 m|
Centre Line Method
Centerline is another method for estimating building work. In this method, as the name indicates, the centre line length of walls, long and short, has to calculate.
You have to calculate the walls’ total centre line length of the same type, long and short, using similar foundations and footings. Now multiply this centerline length with width and height to calculate the quantities of the various work item.
The wall length will be the same for different work items such as excavation in the foundation, foundation concrete, footings and superstructure (with a slight variation in cross walls or the number of junctions).
It is a fast method of estimation but needed special attention and consideration at junctions.
This method is suitable for circular, hexagonal, octagonal, etc., shape buildings with no inner or cross walls.
The buildings with inner or partition wall require special consideration to calculate the exact quantity for each cross or partition wall junction with main walls.
Estimate of Building Work By Centre Line Method
By multiplying the total centre line length with width and depth or height, we can calculate the quantities of different work items.
But when we do this, we take the certain part double and leave an equal part, but it doesn’t affect the quantity.
For instance, the excavation quantity = (AB x 0.90 x 0.90 + BC x 0.90 x 0.90 + CD x 0.90 x 0.90 + DA x 0.90 x 0.90).
Here you can notice that the parts K, L, M and N marked with double hatch line come twice, while the segment P, Q, R and S left blank don’t come at all since these parts are of equal dimension. Hence we get the correct quantity.
From the above Image
Total Centre Length of Wall = AB + BC + CD +DA
= 6.30 + 5.30 + 6.30 + 5.30 = 23.2 m
|1.||Earthwork in Excavation||1||23.2||0.90||0.90||18.79||Total Center length = 23.2|
|4.||Superstructure Brickwork||1||23.2||0.30||0.30||2.088||Deduction for opening have to done.|
I hope now you have enough knowledge and the Long Wall Short Wall method and Centre Line method. Please share it.