The Ontario Building Code | Wall Thickness
9.22.7.2. wall Thickness
(1) The thickness of masonry walls surrounding the smoke chamber shall be not less than 190 mm at the sides, front and back, except that the portions of the back exposed to the outside may be 140 mm thick.
9.22.8. Factory-Built fireplaces
In Plain Language
The smoke chamber's walls must meet a minimum thickness requirement 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.