Estimating is the technique of calculating or Computing the various quantities and the expected Expenditure to be incurred on a particular work or project. In case the funds available are less than the estimated cost the work is done in part or by reducing it or specifications are altered, the following requirement are necessary for preparing an estimate.
a) Drawings like plan, elevation and sections of important points.
b) Detailed specifications about workmanship & properties of materials etc.
c) Standard schedule of rates of the current year.
NEED FOR ESTIMATION AND COSTING:-
1. Estimate give an idea of the cost of the work and hence its feasibility can be determined i..e whether the project could be taken up with in the funds available or not.
2. Estimate gives an idea of time required for the completion of the work.
3. Estimate is required to invite the tenders and Quotations and to arrange contract.
4. Estimate is also required to control the expenditure during the execution of work.
5. Estimate decides whether the proposed plan matches the funds available or not.
PROCEDURE OF ESTIMATING OR METHOD OF ESTIMATING:-
Estimating involves the following operations
1. Preparing detailed Estimate.
2. Calculating the rate of each unit of work
3. Preparing abstract of estimate
DATA REQUIRED TO PREPARE AN ESTIMATE:-
1. Drawings i.e.plans, elevations, sections etc.
2. Specifications.
3. Rates.
DRAWINGS:-
If the drawings are not clear and without complete dimensions the preparation of estimation become very difficult. So, It is very essential before preparing an estimate.
SPECIFICATION:-
a) General Specifications:
This gives the nature, quality, class and work and materials in general terms to be used in various parts of wok. It helps no form a general idea of building.
b) Detailed Specifications:
These gives the detailed description of the various items of work laying down the Quantities and qualities of materials, their proportions, the method of preparation workmanship and execution of work.
RATES:-
For preparing the estimate the unit rates of each item of work are required.
1. For arriving at the unit rates of each item.
2. The rates of various materials to be used in the construction.
3. The cost of transport materials.
4. The wages of labor, skilled or unskilled of masons, carpenters, Mazdoor, etc.,
LUMP-SUM:-
While preparing an estimate, it is not possible to workout in detail in case of petty items. Items other than civil engineering such items are called lump-sum items or simply L.S.Items. The following are some of L.S. Items in the estimate.
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2. Electrical installations like meter, motor, etc.,
3. Architectural features.
4. Contingencies and unforeseen items.
In general, certain percentage on the cost of estimation is allotted for the above L.S.Items.
Even if sub estimates prepared or at the end of execution of work, the actual cost should not exceed the L.S.amounts provided in the main estimate.
WORK CHARGED ESTABLISHMENT:
During the construction of a project considerable number of skilled supervisors, work assistance, watch men etc., are employed on temporary basis. The salaries of these persons are drawn from the L.S. amount allotted towards the work charged establishment. that is, establishment which is charged directly to work. an L.S.amount of 1½ to 2% of the estimated cost is provided towards the work charged establishment.
Measurement of Materials and Works
UNITS OF MEASUREMENTS:-
The units of measurements are mainly categorized for their nature, shape and size and for making payments to the contractor and also. The principle of units of measurements normally consists the following:
a) Single units work like doors, windows, trusses etc., are expressed in numbers.
b) Works consists linear measurements involve length like cornice, fencing, hand rail, bands of specified width etc., are expressed in running metres (RM)
c) Works consists areal surface measurements involve area like plastering, white washing, partitions of specified thickness etc., are expressed in square meters (M2 )
d) Works consists cubical contents which involve volume like earth work, cement concrete, Masonry etc are expressed in Cubic metres.
RULES FOR MEASUREMENT :
The rules for measurement of each item are invariably described in IS- 1200. However some of the general rules are listed below.
1. Measurement shall be made for finished item of work and description of each item shall include materials, transport, labor, fabrication tools and plant and all types of overheads for finishing the work in required shape, size and specification.
2. In booking, the order shall be in sequence of length, breadth and height or thickness.
3. All works shall be measured subject to the following tolerances.
i) Linear measurement shall be measured to the nearest 0.01 m.
ii) Areas shall be measured to the nearest 0.01 sq.m
iii) Cubic contents shall be worked-out to the nearest 0.01 cum
4. Same type of work under different conditions and nature shall be measured separately under separate items.
5. The bill of quantities shall fully describe the materials, proportions, workmanship and accurately represent the work to be executed.
6. In case of masonry (stone or brick) or structural concrete, the categories shall be measured separately and the heights shall be described:
a) from foundation to plinth level
b) from plinth level to First floor level
c) from Fist floor to Second floor level and so on.
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