The quantities of various items such as excavation, foundation concrete, brickwork in foundation and plinth, brickwork in superstructure etc can be calculated by following methods:
- Centre line method
- Long walls and short walls method
- Crossing method
Centre line method :
In this method, sum of total length of centre lines of walls long and short, has to be found out. You can find quantities by multiplying the total centre length by the respective breadth and height. This method is quick but requires special attention and consideration at the junctions, meeting points of cross walls, etc.
Centre line length of one wall = Inner dimension of room + ½ wall thickness of one side + ½ wall thickness of other side
Lets understand this method by one simple example :
Lets assume thickness of wall 0.9 m
Centre line length of horizontal wall = 4 + 0.45 + 0.45 = 4.90 m
Centre line length of vertical wall = 3 + 0.45 + 0.45 = 3.90 m
Total length of centre line = 2 (4.90 + 3.90) = 17.6 m
Now Quantity of excavation for foundation = Total length of centre line of walls x breadth of trench x Depth of trench
= 17.6 x 0.9 x 1.2
= 19.01 m³
For rectangular, circular or polygonal buildings having no inter or cross walls, this method is quit simple but for buildings having cross or partition walls, for every junction of partition or cross walls with main walls, half breadth of the respective item or footing is to be deducted from the total centre length.
Therefor,
Net centre line length = Total centre line length - (½ x breadth of continuous wall x number of junctions)
Long walls and short walls method :
In this method, the longer walls in a building (generally in one direction) are considered as long walls and measured from
out to out. The walls perpendicular to direction of long walls are considered as short walls and are measured from
in to in . These lengths of long and short walls are multiplied separately by the breadth and height of the corresponding layer and are added to get the quantity. Such lengths of long and short walls vary in every layer of footing.
Lets take one example (Refer above figure) :
Length of long wall (horizontal walls) = 4 + 0.9 + 0.9 = 5.8 m
Length of short wall (Vertical walls) = 3 m (because in to in measured length)
Quantity of excavation for foundation = 2 x (5.8 x 0.9 x 1.2) + 2 x (3 x 0.9 x 1.2) = 19.01 m³