In the realm of construction projects, understanding and estimating costs are crucial steps before diving into actual construction. This involves a preliminary or approximate cost estimation, a key factor in gaining administrative approval and making informed decisions. In the commercial domain, such estimates determine if the potential earnings align with the investment.
Preliminary estimates are derived from practical knowledge and the costs associated with comparable projects. They include a detailed report explaining the project’s necessity and utility, complemented by a site or layout plan. A contingency allowance of 5 to 10% is usually factored in for unforeseen circumstances.
Let’s delve into the methods employed for preparing approximate construction cost estimates:
1. Plinth Area Method : The cost calculation in this method revolves around the building’s plinth area, determined by multiplying the length and breadth. The plinth area rate is set after careful consideration of material quality, labor, foundation type, building height, roof, woodwork, and other relevant factors. The calculation involves specific areas per IS 3861-1966, with inclusions such as walls at floor level, internal shafts, barsati at terrace level, and porches, while excluding lofts, unenclosed balconies, and architectural elements like bands and cornices.
2. Cubical Contents Method : Primarily used for multi-storeyed buildings, this method offers a more accurate cost estimate. The calculation involves multiplying the total cubical contents (volume) of the building by the local cubic rate. Volume is determined by measuring length, breadth, and height, excluding plinth offsets. Costs associated with architectural elements like string courses and cornices are neglected in this method.
3. Unit Base Method : In this method, the cost is determined by multiplying the total number of units by the unit rate of each item. For example, in schools, the unit could be ‘one student,’ while in hospitals, it might be ‘one bed.’ The unit rate is derived by dividing the actual expenditure or cost of a similar building in the vicinity by the number of units.
Choosing the appropriate method depends on the nature and complexity of the project. Each method provides a unique perspective, allowing for a comprehensive understanding of the potential costs involved. By employing these methods, stakeholders can make informed decisions during the early stages of project development.
