There are two methods for taking out quantities of various items of works to prepare a building estimate:
1. Separate or Individual Wall Method
In this method, the external lengths of walls running in one direction out to out are taken first from the given drawings and then internal lengths of wall running in the transverse direction are taken into in. The lengths are then multiplied by width and height or depth to take out the quantities. It is better to draw a plan of each wall at foundation level and dealing with each one separately.
Calculation of brick masonry in the foundation is done separately for each step because the width of each step varies. Offsets of the outer walls in foundation masonry are added and in case inner walls subtracted. Thus it shall be seen that the long walls gradually decrease in length while short walls increase in length from foundation to superstructure. This is a simple and accurate method for calculating the various quantities of items.
2. Center Line Method
In this method, the lengths at center lines of all walls worked out. The total length of all long walls of the same size and similarly short walls of same size and type of foundation is worked out and this total length is multiplied by; breadth and height or depth of wall to calculate the total quantities.
Total lengths, in this case, remain the same in all types of calculations i.e., in the foundation, in all steps of footings and in the superstructure. No doubt, this method is quick as compared to the method described above but there may be a mistake of calculations particularly at the junction. For each junction, half breadth of the respective item of the footing is to be deducted from the total center length.
Thus in case, there is one partition wall which has two junctions, deduct one breadth of trench or concrete from the total center length i.e., half breadth for each junction. If there are two partition walls, then two breadths are deducted against four junctions.
A building having different types of walls requires more attention because every wall is to be taken separately. Total length of each type of wall is worked out separately for making the calculation.
NOTE:- 2 length of longwall + 1/2 thickness of both sides wall + length of short wall + 1/2 thickness of both sides wall.