The Ontario Building Code | Cavity Walls
9.20.6.2. Cavity walls
(1) Cavity walls shall be made with not less than 90 mm wide units if the joints are raked and not less than 75 mm wide units if the joints are not raked.
(2) The width of a cavity in a cavity wall shall be not less than 50 mm and not greater than 150 mm.
(3) The minimum thickness of cavity walls above the supporting base shall be 230 mm for the top 7.6 m and 330 mm for the remaining portion, except that where 75 mm wide units are used, the wall height above the top of the foundation wall shall not exceed 6 m.
In Plain Language
Cavity walls, consisting of two masonry wythes with an air space between them, must meet the requirements set out in this article.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.