The Ontario Building Code | Joints in Chimney Liners
9.21.3.2. Joints in Chimney liners
(1) Joints of chimney liners shall be sealed to provide a barrier to the passage of flue gases and condensate into the cavity between the liner and the surrounding masonry.
(2) Joints of clay, concrete or firebrick chimney liners shall be struck flush to provide a straight, smooth, aligned chimney flue.
In Plain Language
Joints in chimney liners must be constructed as set out in this article, preventing gaps that could let heat or combustion gases escape into the surrounding masonry.
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.