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OBC DIVISION B · PART 9 · SECTION 9.4 — STRUCTURAL REQUIREMENTS

What are the basic foundation design rules for houses in Ontario?

Part 9 foundations must bear on undisturbed soil or rock, use footings sized to prescriptive tables based on assumed soil capacity, extend below frost depth, and resist lateral earth pressure with adequate drainage.

Code reference
Foundations must transfer building loads to soil or rock capable of supporting them, with excavations to undisturbed ground. Prescriptive footing and foundation wall sizing applies where soil conditions meet minimum assumed bearing capacity; weaker or disturbed soils, high water tables or unusual loads require design based on subsurface investigation and engineering.
OBC Division B, Subsection 9.4.4. and Section 9.15

Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.

What this means in practice

For typical sites, the footing width tables in Section 9.15 work with an assumed allowable bearing pressure, so no soils report is needed. Red flags that push you to an engineer include fill, organic soil, soft clay, high groundwater, or foundations near slopes. Height of backfill against a foundation wall is limited by wall thickness and type; walkout conditions and tall backfill often exceed prescriptive limits. Combine this with dampproofing, drainage layer, and weeping tile requirements to keep the basement dry and warranty claims away.

Plain language

Your foundation must sit on solid, undisturbed ground below the frost line, with footings sized from code tables. If the soil is soft, wet, or filled, or the design is unusual, an engineer must size the foundation instead.

Related questions

When can you use Part 9 span tables instead of an engineer in Ontario?What design loads apply to houses under Part 9 in Ontario?

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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.