The preparations of detailed construction estimate consist of working out quantities of various items of work and then determine the cost of each item. This is prepared in two stages.
The complete work is divided into various items of work such as earthwork concreting, brickwork, reinforced concrete, plastering etc. The details of measurements are taken from drawings and entered in respective columns of prescribed proforma.
The quantities are calculated by multiplying the values that are in numbers column to Depth column as shown below:
The cost of each item of work is worked out from the quantities that already computed in the detailed measurement form at workable rate. But the total cost is worked out in the prescribed form is known as abstract of estimated form. 4%of estimated Cost is allowed for Petty Supervision, contingencies and unforeseen items.
i) Quantity and transportation of materials: For bigger project, the requirement of materials is more. Such bulk volume of materials will be purchased and transported definitely at cheaper rate.
ii) Location of site: The site of work is selected, such that it should reduce damage or in transit during loading, unloading, stocking of materials.
iii) Local labour charges: The skill, suitability and wages of local labores are considered while preparing the detailed estimate.
The procedure of working out the cost or rate per unit of each item is called as Data. In preparation of Data, the rates of substances and labour are obtained from current standard scheduled of rates and while the quantities of substances and labour needed for one unit of item are taken from Standard Data Book (S.D.B).
The rate per unit of an item includes the following:
1) Quantity of materials & cost: The requirement of materials is taken strictly in accordance with standard data book (S.D.B). The cost of these includes first cost, freight, insurance and transportation charges.
ii) Cost of labour: The exact number of labourers required for unit of work and the multiplied by the wages/ day to get of labour for unit item work.
iii) Cost of machinery (T&P): Some works need special type of machinery, tools and plant. In such case, an amount of 1 to 2% of estimated cost is offered.
iv) Overhead charges: To meet expenses of office rent, depreciation of machinery salaries of staff postage, lighting an amount of 4% of estimate cost is allocated.
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