The Ontario Building Code | Materials
(1) Shingles and shakes shall conform to,
(a) CSA O118.1, "Western Red Cedar Shakes and Shingles", or
(b) CSA O118.2-M, "Eastern White Cedar Shingles".
(2) Western cedar shakes shall be not less than No. 1 grade or Handsplit grade, and western cedar shingles not less than No. 2 grade, except that No. 3 grade may be used for undercoursing.
(3) Eastern white cedar shakes shall be at least B (clear) grade, except that C grade may be used for undercoursing.