Regardless of their type or size, shingles are sold by the square, which is enough material to cover 100 square feet of roof.
In the United States, available lengths are 16″, 18″, and 24″, the length being the vertical side. Widths are random or specified (“dimension shingles”) for a few species. Narrow shingles are less likely to warp than wide ones.
Thickness is based on the average thickness of the thick end (the “butt”) of the shingle, and is described by a fraction: 4/2, for example, means the butts of 4 of the shingles put together measure 2 inches (so they average ½ inch). The two other standard thicknesses are 5/2¼ and 5/2. Thickness is proportional to length: 16″ shingles average 0.40″ thickness; 18″, 0.45″; 24″, 0.50″. Shingles with thick butts are less likely to warp than thin ones.
The direction in which the grain runs also affects the quality of a shingle. Edge-grained shingles, in which the surface of the shingle is perpendicular to the direction of the grain are less likely to warp than flat-grained shingles, in which the surface is tangent to the rings. And finally, heartwood is less likely to decay than sapwood.
Wooden shingles are sawn from western redcedar, northern white-cedar, redwood, and sometimes cypress, each with its own grades:
The top grade of wood shingle is 100% clear (that is, free of knots), edge-grain heartwood. As an example of definitions of lower grades, in #2 grade 10″ of a 16″ shingle must be clear, 11″ of an 18″ shingle, and 16″ of a 24″ shingle. For #3, a utility grade, 6″ of a 16″ shingle and 10″ of a 24″ shingle must be clear.
Since shingles are overlapped, only a portion shows, which is called the “exposure”. The longer the shingle and the steeper the slope, the greater the exposure can be. For example, on a roof that rises 5″ in a foot, 7½″ of a 24″ shingle would show, but on a roof that rises 3" in a foot, only 3¾″ of a 16″ shingle would show.
English shingles of the early 1700s were much smaller than ours: 6-8″ broad and 12″ long.¹
[Western red cedar] SHINGLES 16 inches long, the smallest size, must be so thick that five shingles, when measured across the butts (or thickest portion) when green must measure two full inches. As these shingles are packed in bundles with twenty courses on each side of the band-sticks, the bundle must therefore measure 8 inches in thickness when green. If measured after seasoning has occurred, an allowance of ¼ inch is made for shrinkage. In the lowest grade, an additional allowance of ¼ inch is made for variation in sawing.
Bror L. Grondal
Certigrade Handbook of Red Cedar Shigles, 10th ed. rev.
Seattle/Vancouver: Red Cedar Shingle Bureau, 1957.
The most common size is the “strip shingle,” 12″ by 36″, with either 2 or 3 tabs.
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Last revised: 10 June 2019.