The Ontario Building Code | Cold Weather Requirements
9.3.1.9. Cold Weather Requirements
(1) When the air temperature is below 5°C , concrete shall be,
(a) kept at a temperature of not less than 10°C or more than 25°C while being mixed and placed, and
(b) maintained at a temperature of not less than 10°C for 72 h after placing.
(2) No frozen material or ice shall be used in concrete described in Sentence (1).
9.3.2. Lumber and wood Products
In Plain Language
Concrete placed in cold weather needs special precautions set out in this article, since freezing temperatures can prevent concrete from curing properly and reaching its design strength.
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.