This section is from the book "The Building Trades Pocketbook", by International Correspondence Schools. Also available from Amazon: Building Trades Pocketbook: a Handy Manual of reference on Building Construction.
An approximate figure for cost of plumbing is 10 per cent, of the cost of the building. This figure is for good materials and labor, and of course is subject to considerable variation. For an ordinary house, costing from $1,500 to $3,000, the cost of plumbing may be taken as about 8 per cent, for moderate-priced fixtures and public sewer service. The cost of labor alone will average about 1/4 the cost of the materials.
The cost of gas-fitting may be approximately figured as about 3 per cent, of the cost of the building. The cost of labor alone varies from about 1/4 to 1/7 the cost of materials. The better the grade of fixtures, the lower will be the ratio - provided there is no excessive ornamentation, requiring much time to put in place - as the cost of the labor is about the same for cheap fixtures as for more costly ones.
In estimating on heating by furnace, the average cost of labor is about 1/3 that of materials. In steam and hot-water heating, the ratio is about 1/5.
Hard ware is best estimated by noting the quantities required for each portion of the work as it is being measured, afterwards making these items into a separate hardware bill. Many of the articles, as, for example, the number of fixtures for doors or window trimmings, may be readily counted from the plans. Hardware for windows, doors, etc., are sometimes included in estimating the cost per window, door, etc., and are not considered separately. The cost of hardware depends entirely on the class of work and finish desired, and the best way to estimate on it is, after making the schedule, to select suitable designs and figure the prices from a catalogue. An approximate estimate for ordinary buildings is 1 1/2 per cent, of the cost of the building, From 15 to 20 per cent, of the cost of hardware will pay for the putting in place.