The Ontario Building Code | Fire Exposure
9.10.3.3. Fire Exposure
(1) floor, roof and ceiling assemblies shall be rated for exposure to fire on the underside.
(2) exterior walls shall be rated for exposure to fire from inside the building, except that such walls need not comply with the temperature rise limitations required by the standard tests referred to in Article 9.10.3.1. if such walls have a limiting distance of not less than 1.2 m, and due allowance is made for the effects of heat radiation in accordance with the requirements in Part 3.
(3) Firewalls and interior vertical fire separations required to have fire-resistance ratings shall be rated for exposure to fire on each side.
In Plain Language
Fire-resistance ratings must be based on the fire exposure conditions described in this article, reflecting standardized testing that determines how materials perform under real fire conditions.
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.