The Ontario Building Code | Thickness

9.29.7.2. Thickness

(1) Hardboard shall be not less than,

(a) 3 mm thick where applied over continuous back-up,

(b) 6 mm thick where applied to supports spaced not more than 406 mm o.c., and

(c) 9 mm thick where applied to supports spaced not more than 610 mm o.c.