Wood Roof Shingles Grade

(1)  Western cedar shingles shall be not less than No. 2 grade.

(2)  Eastern white cedar shingles shall be not less than B (clear) grade.

Article 9.26.9.2. Ontario Regulation 332/12 Building Code,   Information published by oncodes.ca for educational purposes only.

Wood Shingles

Note : Western red and white cedar are the principal species of wood used for shingles because their
heartwoods have high decay resistance and low shrinkage (they may also be preservative-treated). Other species are also used for shingles but should be preservative-treated. Wood shingles commonly for houses are No. 1 and No. 2 grade.

Source : Canada Mortgage and Housing Corporation (CMHC)