=55. Kinds of Roof Covering.=—The =roof coverings= most generally used
are shingles, slate, tin, tile, and tarred paper and gravel (known as
gravel roofing). While there are slight variations in the methods of
measuring the different kinds, they are all based on the square of 100
square feet.
=56. Shingles.=—In measuring =shingle roofing=, it is necessary to
know the exposed length of a shingle. This is found by deducting 3
inches (the usual cover over the head of the lowest shingle in the four
overlapping courses) from the length and dividing the remainder by 3.
Thus, in Fig. 5, the distance _b_ that one shingle is overlapped by the
third above it is usually made equal to 3 inches, and the remaining
length of the lowest shingle may be divided into three equal portions,
each equal to _a_. The lowest of these three portions is the part
exposed to the weather. Multiplying the length exposed to the weather
by the average width of a shingle will give the exposed area. Dividing
14,400, the number of square inches in a square, by the exposed area
of 1 shingle, in square inches, will give the number of shingles
required to cover 100 square feet of roof. For example, it is required
to compute the number of shingles 18 in. × 4 in. needed to cover 100
square feet of roof. With a shingle of this length, the exposure will be
18 - 3
------ = 5 inches;
3
then, the exposed area of 1 shingle is 4 in. × 5 in., or 20 square
inches, and 1 square requires 14,400 ÷ 20 = 720 shingles.
[Illustration: FIG. 5]
An allowance should always be made for waste in estimating the number
of shingles required.
Table X is arranged for shingles from 15 to 27 inches in length, 4 and
6 inches in width, and for various lengths of exposure.
=57.= Shingles are classed as _shaved_, or _breasted_, and _sawed
shingles_.
=Shaved shingles= have fallen almost into disuse, owing to the
difficulty of manufacturing them. These shingles vary from 18 to 30
inches in length, and are about ½ inch thick at the butt and ¹/₁₆ inch
at the top.
=Sawed shingles= are usually from 14 to 18 inches long and of various
thicknesses. In the case of 18-inch shingles, five shingles, at their
butts, will make 2¼ inches; that is, the thickness of one shingle at
the butt is 2¼ ÷ 5 = .45, or about ⁷/₁₆ inch. At the top, each shingle
is ¹/₁₆ inch thick. With 16-inch shingles, however, five of them make
only 2 inches. Therefore, the thickness of a 16-inch shingle at the
butt is 2 ÷ 5 = .4, or about ⅜, inch.