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Methods of preparation of preliminary or**approximate construction cost estimation**for studies of various aspects of work of project and its administrative approval is discussed. This estimate can decide, in case of commercial projects, whether the net income earned justifies the amount invested or not. The approximate estimate is prepared from the practical knowledge and cost of similar works. The estimate is accompanied by a report duly explaining necessity and utility of the project and with a site or layout plan. A percentage 5 to 10% is allowed for contingencies.

Contents:

**Methods of Approximate Construction Cost Estimation Preparation**

The following are the **methods used for the preparation of approximate construction cost estimates:**

- Plinth area method
- Cubical contents method
- Unit base method

**a) Plinth area method: **

The cost of construction is determined by multiplying the plinth area with the plinth area rate. The area is obtained by multiplying length and breadth (outer dimensions of the building).
In fixing the plinth area rate, careful observation and necessary inquiries are made in respect of quality and quantity aspect of materials and labor, type of foundation, the height of building, roof, woodwork, fixtures, number of stories, etc.
**As per IS 3861-1966, the following areas include while calculating the plinth area of the building:**

**Types of Estimates:**

- Area of walls at floor level.
- Internal shafts of sanitary installations not exceeding 2.0 sqm, lifts, air-conditioning ducts, etc.,
- Area of barsati at terrace level: Barsati means any covered space open on one side, constructed on one side, constructed on the terraced roof which is used as shelter during the rainy season.
- Porches of non-cantilever type.

**Areas which are not to include**

- Area of lofts.
- Unenclosed balconies.
- Architectural bands, cornices, etc.,
- Domes towers projecting above terrace level.
- Box louvers and vertical sun breakers.

**b) Cubical Contents Method:**

This method is generally used for multi-storeyed buildings. It is more accurate than the other two methods viz., plinth area method and unit base method.
The cost of a structure is calculated approximately as the total cubical contents (Volume of buildings) multiplied by Local Cubic Rate. The volume of the building is obtained by Length x breadth x depth or height.
The length and breadth are measured out to out of walls excluding the plinth offset.
The cost of string course, cornice, corbelling, etc., is neglected.
**The cost of building = volume of buildings x rate/ unit volume.**

**c) Unit Base Method:**

According to this method, the cost of the structure is determined by multiplying the total number of units by a unit rate of each item. In the case of schools and colleges, the unit considered to be 'one student', and in the case of a hospital, the unit is 'one bed'.
The unit rate is calculated by dividing the actual expenditure incurred or cost of a similar building in the nearby locality by the number of units.
**Also Read:**

**Methods of Detailed Construction Estimation Preparation**