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.
In estimating tin (and also other metal) roofs, hips and valleys are measured extra their entire length by 1 ft. in width, to compensate for increased labor and waste of material in cutting and laying. Gutters and conductor, or leader, pipes are measured by the lineal foot, 1 ft. extra being added for each angle. All flashings and crestings are measured by the lineal foot. For seams, addition is made to superficial area, depending on the kind of seam used, whether single-lock, standing, or roll-and-cap. No deductions are made for openings (chimneys, skylights, ventilators, or dormer-windows), if less than 50 sq. ft. in area; if between 50 and 100 sq. ft., one-half the area is deducted; if over 100 sq. ft. the whole opening is deducted. An extra charge is made for labor and waste of material to flash around such openings.
A box of roofing tin contains 112 sheets 14 in. X 20 in., and weighs from 110 to 140 lb. per box, according to whether it is IC or IX plate. The IC plate, which is the most used, weighs about 8 oz. per sq. ft., and the IX, about 10 oz. As there are considerable variations in the weights of tin made by different manufacturers, a fair average will be obtained by estimating IC tin at 1 lb., and IX tin at 1 1/4 lb., per sheet. Double-size roofing tin can be had 20 in. X 28 in., weighing, if IC, 225 lb. per box. This size is the most economical, as by its use much material and labor are saved, on account of the less number of seams and ribs required.
A 14" X 20" sheet will cover about 235 sq in. of surface, using standing joints; or a box will cover about 182 sq. ft. With a flat-lock seam, a sheet will cover 255 sq. in., allowing | in. all around for joints; or a box will lay 198 sq. ft. These figures make no allowance for waste.
Two good workmen can put on, and paint outside, from 250 to 300 sq. ft. of tin roofing per day of 8 hours. Tin roofing will cost from 8 to 10 cents per sq. ft., depending on the quality of material and workmanship.
Tile roofs are constructed of so many styles of tile that no general rules of measurement can be given, and every piece of work must be estimated according to the particular kind of tile used and the number of-sizes and patterns. Information on all these points are to be found in the catalogues of tile manufacturers.
In gravel roofing, the cost per square depends on the number of thicknesses of tarred felt and the quantity of pitch used per square. _______