Estimation and specification can be a difficult topic in the field of architecture and construction. But understanding the whats and whys of the process makes it very easy.
The most complicated type of estimation is the detailed estimate. Detailed estimate consists of complete and thorough calculation of the costs of every single resource and service of a project and should be delivered before the construction begins.
Using the centerline method, all the total lengths are added, after which the overlaps that occur in T-junctions are excluded.
In this method, the volumes of the structures are calculated first. After the values are obtained, it is multiplied to the rates of each material used, giving us the total amount required.
(This example only has details for brick wall construction)
The first step is to get the total length of the structure. Since there are two types of walls in the plan, calculations must be done separately for each.
In the example problem, the plan of the wall structure is shown. For the 0.3 m thick wall:
For the 0.2 m thick wall:
A basic construction consists of a superstructure and substructure. Substructure consists of foundation. Superstructure consists of everything above the plinth level, that is, the walls, DPC, plaster and whitewash.
For each of the above categories, calculate individual lengths by using the given formula:
L= l-n*b/2 (where L is required length, l is the added length, n is the number of T junctions and b is breadth)
For example, taking earthwork for 0.3 m thick wall,
Therefore, L= 65.9-(6*0.9/2)= 63.3 m
Use the same method and formula to calculate the individual lengths for each of the elements in the table.
In this step, the total volume of each structure is calculated.
The last step is to calculate the rates.
A percentage of the cost goes to transportation and contractor’s charges.
Although these are the basic steps used to calculate detailed estimation, it has further steps, where the materials used to build the structures are taken separately and rates are calculated for them. Labour and service costs are also done separately.