Approximate estimate is made to find out an approximate cost in a short time, without taking out actual quantities. This enables the responsible authority to consider the financial aspect of the scheme.
The accuracy of the cost estimated by such approximate estimate depends upon the judgement, skill and experience of the estimator and upon the correctness of the prices. It is required for preliminary studies of various aspects of a work or project to decide the financial position and policy for administration sanction by the competent authority like Municipal corporation, development authority etc.
In case of commercial projects as Irrigation, Residential buildings and other similar projects which earns revenue income, the probable income may be worked out. From the preliminary estimate the approximate cost may be known and then income and cost is studied. If it is justified to go for project then further detailed estimates are prepared.
Watch the following lecture to get an proper information about the approximate estimation of building.
In case of non-commercial projects Or project which do not give direct return, necessity, utility and money available can be studied. In this type of estimate all important works like cost Of land, cost Of each building, cost Of roads etc. are shown separately.
Approximate estimate is prepared to decide the financial aspect, administrative approval, for sending the proposal and appraisal of various civil engineering projects. For different type of structures like buildings, roads, bridges, railways etc. approximate estimate is prepared from practical knowledge and cost of similar work is executed in past. It shows separately cost of land, building, road,
water supply, sanitary work etc.
There are following methods of preparing approximate estimates:
(1) Plinth area rate method
(2) Cubical content method
(3) Service unit method
(4) Typical bay method
(5) Approximate quantity method.
1. Plinth Area Rate Method :
This estimate is prepared on the basis of plinth area of building. The rate for unit plinth area is determined from the cost of similar building having similar specifications, heights, construction and locality.
Plinth area estimate is prepared by finding the plinth area of the building and multiplying by the plinth area rate. Plinth area should be calculated for the covered area by taking the external dimensions of building at the floor level. This area must not include area of court yard, open passages etc.
For a multi-storeyed building the plinth area estimate is prepared for each storey separately. Plinth area estimate is a type of approximate estimate. If the plan of the building is not ready then total carpet area and 35% extra area gives plinth area.
2 Cubical Content Method:
It is an approximate estimate. It is prepared on the basis of cubical content of the building. The cube rate is determined from the cost of similar building having similar specification and construction in the locality. This is calculated by finding the cubical content of the building (f x b x h) and multiplying it by cube rate.
It is more accurate as compared to plinth area estimate. The cubical content Of building must not include foundation, plinth and parapet above roof.
3 Approximate Quantity Method:
To find the running metre rate of foundation, the approximate quantities of items such as excavation, foundation, brick work upto plinth, D.P.C., are calculated per running metre of walls. By calculating price per running metre, rate is determined.
Similarly, for super structure also, the price or rate per running metre is determined from approximate quantities of brick work, wood work, roofs, floors etc. For this method plan of building must be available.
In this method, approximate total length of walls is found in running metre (RMT) and this total length is multiplied by the rate per running metre of wall. For this, a structure is divided into two parts :
1. Foundation (Including plinth).
2. Super structure.
The running metre cost for foundation and super structure should be calculated first and then running metre rate should be multiplied by total length of walls. For this method plan of building must be available.
4 Service unit Method:
Each building is constructed to serve some purpose. For example, a hospital is designed to accommodate certain number of beds. Each bed is then considered as service unit of a hospital building. Whenever a building is constructed, the engineer keeps the record of the place of construction, actual cost of construction, number of service units etc. From this record, it is possible to work
out the cost of construction per service unit.
While preparing approximate estimate by this method per student for hostels, per student for schools, per class room for schools, per bed for hospitals, per seat for cinema halls, per bay for factories, is considered.