The weight per square foot of any roof may be quite closely estimated from the following data:

Shingles, common, 2 1/2 lbs.; 18 ins., 3 lbs.

Slates, 3-16 in. thick, 7 1/4 lbs.; 1/4 in. thick, 9.6 lbs. (the common thickness is 3-16 in. for sizes up to 10"x20").

Plain tiles or clay shingles, 11 to 14 lbs.

Roman tiles, old style, two parts, 12 lbs.; new style, one part, 8 lbs.

Spanish tiles, old style, two parts, 19 lbs.; new style, one part, 8 lbs.

Improved Oriental tiles, 11 lbs."

Ludowici tile, 8 lbs.

For tiles laid in mortar add 10 lbs. per square foot.

Copper roofing, sheets, 1 1/2 lbs.; tiles, 1 3/4 lbs.

Tin roofing, sheets or shingles, including one thickness of felt, l lb.

Corrugated iron, painted or galvanized, No. 26, 1 lb.; No. 24, 1.3 lbs.; No. 22, 1.6 lbs.; No. 20, 1.9 lbs.; No. 18, 2.6 lbs.; and No. 16, 3.3 lbs.

Standing seam steel roofing, 1 lb.

Five-ply felt and gravel roof, 6 lbs.

Four-ply felt and gravel roof, 5 1/2 lbs.

Three-ply ready roofing (elaterite, ruberoid, asphalt, etc.), 0.6 to 1 lb.

Skylights with galvanized iron frame, 1/4 inch glass, 4 1/2 lbs.; 5-16 in., 5 lbs.; 3/8-in., 6 lbs.

Sheathing, 1 in. thick, 3 lbs. per square foot for white pine, spruce, or hemlock; 4 lbs. for yellow or pitch pine.

The dimensions and weight of wooden rafters may be taken from tables V. and VI.