The Ontario Building Code | Combustible Interior Finish
3.1.5.10. Combustible interior Finish
(1) Combustibleinterior finish, including paint, wallpaper, and other interior finishes not more than 1 mm thick, is permitted in a buildingrequired to be of noncombustible construction.
(2) Combustible interior wall finishes, other than foamed plastics, are permitted in a building required to be of noncombustible construction provided they,
(a) are not more than 25 mm thick, and
(b) have a flame-spread rating not more than 150 on any exposed surface, or any surface that would be exposed by cutting through the material in any direction.
(3) Combustibleinterior ceiling finishes, other than foamed plastics, are permitted in a building required to be of noncombustible construction provided they,
(a) are not more than 25 mm thick, except for exposed fire-retardant treated woodbattens, and
(b) have a flame-spread rating not more than 25 on any exposed surface, or on any surface that would be exposed by cutting through the material in any direction, or are of fire-retardant treated wood, except that not more than 10% of the ceiling area within each fire compartmentis permitted to have a flame-spread rating not more than 150.
In Plain Language
This clause allows several categories of thin combustible interior finish (paint, wallpaper, finishes under 1 mm) without restriction in noncombustible-construction buildings, and permits thicker combustible wall finishes (up to 25 mm, flame-spread rating 150 or less) and ceiling finishes (up to 25 mm, with its own flame-spread cap) under specific conditions, excluding foamed plastics in both cases.
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.