October 2, 2017 BoQ No Comments
Quantity Takeoff
Depending on the shape or design of a building the method of taking out quantities also varies. Here, I describe the more common methods of taking out quantities in the construction field.
Long wall & short wall method
Also called as general method, separate method, out-to-out & in-to-in method or individual wall method. This method is especially applicable for the works such as foundation, excavation & foundation concrete. This method is described as follows,
- First, find out the lengthy wall (they are the long wall and wall perpendicular to that is short wall).
- Then find the measurements of external length of lengthy wall (that is out-to-out) and internal length of short wall (in-to-in) and height of the wall.
- Finally multiply them to find out the necessary quantity, long wall (out-to-out) OR short wall (in-to-in) X breadth of wall X height.
In the given below diagram, the green coloured layers are long walls and other layers represent the short walls. The “arrow mark” on the green layer shows how the length of a long wall should be measured (out-to-out) and the “arrow mark” on the other layer shows, how a short wall should be measured (in-to-in).
Here is the short cut for you
Long wall (out-to-out) = c/c length + 1/2 breadth on one side + 1/2 breadth on the other side
= c/c length + one breadth.
Short wall length in-to-in = c/c length – 1/2 breadth on one side – 1/2 breadth on the other side
= c/c length – one breadth.
Additional info:
Length of long wall measurement decreases while length of short wall measurement increases, when notice the measurements from foundation to super structure.
Example.
Calculate the quantity of excavation for the given plan using long wall – short wall method?
Centreline Method
This is another method of taking out quantities for construction estimation. This method is easy or quick as to calculate even from work site. But the method is more suitable if the offsets of the building are symmetrical. The center line act as “length” for calculation of an estimate by this method. Here, the center line is multiplied by breadth and the height to take out the necessary quantity (center line X breadth of wall X height). But the calculations should be carefully noticed in junctions or cross walls such as L, T or +.
Here, the green coloured area will be calculated twice when takeoff quantity. So the green coloured area should be deducted once from the measurement when takeoff quantity.
Here the green coloured area will be calculated twice when takeoff quantity. But the measurement of blue coloured area will not be included in any instance such as when calculate the measurement of yellow coloured area or when calculate the silver coloured area. So there is o need to add or deduct anything to the measurement when takeoff quantity.
Here, the green coloured area will be calculated twice when takeoff quantity. So the green coloured area should be deducted once from the measurement when takeoff quantity.
Short cut and additional info
“ L “ Junction – There is no need to deduct from total centreline length.
“ T “ Junction – Half (1/2) breadth wall measurement should be deducted for a T junction.
“ + “ walls / cross walls – Wall breath measurement should be deducted to the total length of centreline.
Example:
Calculate the quantity of excavation for the given plan using centreline method?
