How deep must you excavate below frost for foundations in Ontario?
Foundations must extend below the depth of frost penetration, commonly about 1.2 m (4 ft) across much of southern Ontario and deeper in northern regions, unless bearing on rock or protected from frost, with minimum depths set by soil type and heating.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
Frost depth is a local value: many southern Ontario municipalities enforce 1.2 m, while northern areas commonly require 1.8 m or more, so check with your building department rather than assuming. Unheated structures like detached garages and deck piers need full frost depth because they get no warmth from the building; helical piles and insulated shallow foundations are engineered alternatives. Frost heave can lift a footing and crack the structure above, and it acts strongest on isolated piers, which is why heaved deck footings are so common.
Footings must sit below the level where the ground freezes, about 1.2 m down in much of southern Ontario and deeper up north. Otherwise winter frost can literally lift your foundation and crack the building.
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This page is provided for general information. Building code requirements depend on your specific project, occupancy and municipality, and code editions change. Always verify requirements against the current Ontario Building Code and confirm with your local building department.