The Ontario Building Code | Nailing Elements
3.1.5.6. Nailing Elements
(1) wood nailing elements attached directly to or set into a continuous noncombustible backing for the attachment of interior finishes, are permitted in a building required to be of noncombustible construction provided the concealed space created by the wood elements is not more than 50 mm thick.
In Plain Language
Wood nailing elements attached to a continuous noncombustible backing (used to fasten interior finishes) are allowed in noncombustible-construction buildings, as long as the concealed space they create is no more than 50 mm thick.
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.