Unit Method Of Approximate Estimate
It is also known as preliminary estimate. It is undertaken for making studies of different phases of work of project and for its administrative authorization. This type of estimate can determine for any commercial project, whether the net income gained substantiates the amount invested or not.
The approximate estimate is made from the practical knowledge and cost of equivalent works. The estimate is led by a report that precisely narrates necessity and effectiveness of the project as well as with a site or layout plan. For contingencies, there should be 5 to 10% allowance.
The approximate estimates is created with the following methods :-
- Plinth area method
- Cubical contents methods
- Unit base method
Also read : METHODS OF MEASURING QUANTITIES IN STRUCTURE
Plinth Area Method
The cost of construction is set by multiplying plinth area with plinth area rate. The area is produced by multiplying the length and breadth (exterior dimensions of the building). While settling the plinth area rate, careful examination and vital enquiries are provided with regards to quality and quantity aspect of materials & labor, type of foundation, hight of building, roof, wood work, fixtures, number of stories etc.
According to IS 3861-1966, the following areas should be taken into consideration at the time of measuring the plinth area of the building :
- Area of walls at floor level
- Internal shafts of sanitary installations not surpassing 2.0m2, lifts, airconditioning ducts etc
- Area of barsati at terrace level
- Barsati stands for any covered space open on one side, constructed on one side and on terraced roof which is applied as shelter throughout rainy season.
- Porches of non cantilever type
Areas which are excluded :-
- Area of lofts
- Unenclosed balconies
- Architectural bands, cornices etc
- Domes, towers projecting over terrace level
- Box louvers and vertical sun breakers
Cubical Contents Method
This method is normally applied for multistoried buildings. It is more authentic as compared to other two methods given above. The cost of a structure is measured roughly as the total cubical contents (volume of buildings) multiplied with local cubic rate. To get the volume of building, the formula is used as Length x Breadth x Depth or Height. The length and breadth are measured outside to outside of the walls devoid of the plinth off set.
- The cost of string course, cornice, carbelling etc. is omitted
- The cost of building = Volume of buildings x rate/unit volume
Unit Base Method
As per this method, the cost of structure is obtained by multiplying the total number of units with unit rate of each item. For schools and colleges, the unit considered to be as ‘one student’ and for hospital, the unit is ‘one bed’. The unit rate is measured by dividing the actual expenses done or cost of related building in the adjacent locality by the number of units.
