The Ontario Building Code | Fire-Retardant Treated Wood
3.1.4.5. Fire-Retardant Treated wood
(1) If fire-retardant treated wood is specified in this Part, the wood shall,
(a) be pressure impregnated with fire-retardant chemicals in conformance with CAN/CSA-O80 Series-M, "wood Preservation", and
(b) have a flame-spread rating not more than 25.
In Plain Language
Where the Code calls for fire-retardant treated wood, this clause requires it to be pressure-impregnated with fire-retardant chemicals per the CAN/CSA-O80 standard and to achieve a flame-spread rating of 25 or less.
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.