Coverage of Asphalt Shingles on Slopes of 1 in 3 or Greater

(1)  Coverage shall be not less than two thicknesses of shingle over the entire roof, disregarding cutouts.

Article 9.26.7.1. Ontario Regulation 332/12 Building Code,   Information published by oncodes.ca for educational purposes only.

Asphalt Shingles on Slopes 1:3 or Greater

Asphalt strip shingles should be a minimum No. 210 grade. Square-butt strip shingles are usually 310 × 915 mm (12 × 36 in.) or 335 × 1 000 mm (131⁄4 × 39 3⁄8 in.) in size, have three tabs and should be laid with 130 mm (5 in.) or 145 mm (5¾ in.) of their width exposed to the weather. Since there are approximately 21 to 26 strips in a bundle, a bundle will cover about 3 m2 (32 sq. ft.).

Store bundles flat so that strips will not curl when the bundles are opened. Distribute the storage of shingles on roofs so that the load capacity of the framing is not exceeded.

Source : Canada Mortgage and Housing Corporation (CMHC)