Before undertaking the construction of a project, it is necessary to know its probable cost which is calculated out by estimating. An estimate is the computation or calculation of quantities required and expenditure likely to be incurred in the construction of the work.
The primary object of the estimate is to enable one to know the approximate cost of the work( building, structure etc). The estimate is also defined as the probable cost of the work and is determined theoretically by a mathematical calculation based on the drawing and plans and current rates. The approximate estimate may be prepared by various method but the accurate estimate is prepared by a detailed estimate.
Importance of estimate
1. It helps in working out the approximate cost of work.
2. It is useful to check out the work done by the contractor during and after the execution.
3. Payment to the contractor is done according to the actual measurement.
4. It gives an idea for the requirement of controlled materials like brick, cement, and steel etc.
5. By framing a complete estimate, the client can advise on
a. Valuation of properties on(land valuation and building)
b. Fixation of the standard rate.
c. the sale price of flats in case of a building is constructed on an ownership basis.
d. For claiming the amount of building in arbitration proceedings.
Data required for the preparation of estimate
Drawing of completely and fully dimension i.e(plans, sections, elevation and related other details) are required.
The detailed specification describes nature, quality and class of work, materials to be used in the various parts of work, quality of materials method of preparation and description of the execution of work.
The rates of different items of work, material to be used in the construction of work and the wages of different categories of labour should be available for preparing an estimate. The cost of transportation should also be known. The rates may be worked out by the analysis of rates method.
After collection of the above information, the estimate is worked out.
4. Updated mode of measurement for standard deductions or additions is also necessary to determine the correct quantities of works.
5. Standing circulars for taxes and insurance etc are required to fix up rates of those items which are not in the schedule of rates.
Factors considered during the preparation of a detailed estimate are :
1. Quantity of materials
A large quantity of materials is required and this can be purchased at a rate cheaper than the rate of materials required for minor work, for large construction. Therefore, the rate of works must be framed considering the volume of work.
2. Availability of materials
The estimated cost of a specific item is higher than the scheduled rate if there is no reassurance that the materials will be available as and when required, and it is detrimental to the progress of the work if the workers and the maintenance staff remain idle for the paucity of materials.
3. Transportation of materials
If smaller quantities of material are required to be transported to a considerable distance the proportionate cost of transportation becomes higher in comparison with the cost of a larger quantity transported at a time.
4. Location of site
If the site of work is located at a strange place for which loading, unloading, stacking and restocking of materials are necessary, several times, due to different kinds of the journey, the possibility of damage or loss in transit should be considered carefully.
5. local labour charges
Skill and daily wages of the local labourer should be considered before the preparation of a detailed estimate.
Types of Estimate
1. Preliminary Estimate
This is an estimate to find out an approximate cost in a short time. This is also a rough estimate made in the early stage of design work in any project. In the case of the commercial projects such as irrigation project, building project and similar other projects, the probable cost may be worked by the preliminary instrument.
Example; unit basis
-per classroom for school
-per bed for hospital
-per seat of move theatre etc
approximate cost of the hospital building
For beds at Rs 10,000 per bed
2. Plinth area Estimate
This estimate is prepared on the basis of plinth area of the building. The area is calculated and multiplied by plinth area rates. For stories building, the plinth area estimate is prepared for each storey.
For example; The approximate cost of buildings having plinth area of 100 square meters at 900 rupees per square meter,
cost of building=100*900
3. Cubic rate Estimate or volume rate Estimate
The cubic rate estimate is calculated by finding the cubical content of building (l*b*h)
and multiplied by the cube rate. The length and breadth should be taken from the external dimension of the buildings. For storeyed building, the height should be taken between the floor level of one-storeyed to top of next floor. The cube rate estimate is most accurate as compared to plinth area estimate.
4. Approximate quantity of the material estimate
In this method, the approximate total length of the wall is found in running meter and this total length is multiplied by the rate per running meter of the wall which gives a fairly accurate cost. The running meter cost of foundation and superstructure should be calculated first.
To find the running meter rate per foundation. The DPC is calculated per running meter and multiplied with the rate of these items. Similarly, for the superstructure, the rate per running meter is determined from the approximate quantities of brickwork and other items too.
5. Detailed estimate (Item rate Estimate)
It is an accurate estimate and consists of working out the quantities of each item of work and working out the cost. The dimensions length, breadth and thickness of each item are taken out correctly from the drawing and quantities of each item are calculate and billing is done. The detailed estimate is done in two stages ;
a. Details of measurement
b. Abstract of cost
6. Revised Estimate
The revised estimate is a detailed estimate and is required to be prepared under any one of the following estimates;
1. When the original sanctioned estimate is exceeded or likely to exceed by more than 5%.
2. When the charges on a work exceed or likely to exceed, the amount of administrative sanctioned by more than 10%.
3. When there is a material deviation from the original proposal.
7. Supplementary Estimate
Supplementary Estimate is prepared when the extra work is required to supplement the original work when further development is required during the progress of work. This is the freshly detailed estimate of the additional work in addition to the original estimate.
8. Annual repair and maintenance Estimate
It is a detailed estimate and prepared to maintain the structure of all work in proper order and safe condition for building. This includes whitewashing painting, minor repairs, for the road the annual repair estimate provide patch repairing repair of bridges and culvert etc.
9. A complete Estimate
This estimate is prepared in standard form which consists of :
1. Title page giving them of engineering items, name of work, amount of estimate etc.
2. Index of contents plans and drawing
4. Design and calculation
5. General specification
6. Detailed specification
7. Analysis of rates
8. Details of measurement and calculation quantities.