Procedure of preliminary estimate (office building)

A preliminary estimate is prepared by the plinth area method, as follows. It is for the administrative approval, so the drawings are not yet detailed.

Steps

1. Establish the requirement: the number of staff and rooms, and from these the total carpet area (usable floor area) from the norms for office space per person.
2. Find the plinth (built-up) area:

$$\text{Plinth area} = \frac{\text{Carpet area}}{1 - (\text{circulation \%} + \text{wall \%})}$$

The circulation area (corridors, verandah, stairs, toilets) is taken as 20 to 30% and walls as 8 to 10% of the plinth area. 3. Select the plinth area rate prevailing in the locality (or the DUDBC / department rate) for the type of building. 4. Building cost = plinth area x plinth area rate. 5. Add the extras as percentages of the building cost: special architectural treatment, water supply and sanitary works, electrical installation (and lift), deep foundation, and other services. 6. Add external services: compound wall, approach road, drainage, septic tank and landscaping. 7. Add contingency (3 to 5%) and supervision/departmental charge (3 to 8%). 8. Total is the estimate for approval.

Example (assumed)

Carpet area 1,000 m²; circulation 30% and walls 10%, so plinth area = 1000 / 0.6 = 1,666.67 m². Plinth area rate Rs 20,000 per m² gives a building cost of Rs 33.33 million. Electrical at 8% and other services at 5% add Rs 4.33 million. Contingency 5% and supervision 5% are then added on the total. The result, about Rs 41.4 million, is submitted for approval.