Overhead. This may include construction plant, office expense, supervision, bond, interest on borrowed capital, insurance, transportation, etc. The amount of the item is seldom less than 15 per cent and is usually over 20 per cent of the contract price.
Contingencies. This allowance is usually 10 to 15 per cent of the contract price.
Profit. This should be from 5 to 10 per cent of the sum of the four preceding items.
The contract price is the sum of these items. To this may be added:
Engineering. 2 to 5 per cent of the contract price.
Extra Work. Zero to 15 per cent of the contract price; dependent on the character of the work, the completeness of the preliminary information, the completeness of the plans, etc.
Legal expense.
Purchase of land, rights of way, etc., etc.
The cost of the sewer may be stated as so much per linear foot for different sizes of pipe, including all appurtenances such as manholes, catch-basins, etc., or the items may be separated in great detail somewhat as follows:
Earth excavation, per cu. yd.