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OBC DIVISION B · PART 9 · SECTION 9.17 — COLUMNS

What size footing does a basement column need in Ontario?

Column footings come from the OBC footing tables: for columns spaced about 3 m (10 ft) apart, minimum areas are roughly 0.4 m² supporting one floor, 0.75 m² for two and 1.0 m² for three, on adequate soil, with thickness at least 100 mm and not less than the footing projection.

Code reference
Footings under columns in Part 9 buildings must be sized from the prescriptive tables, which give minimum footing areas based on the number of storeys supported and assume typical column spacing and adequate soil bearing. Footings must be centred under their columns, be at least 100 mm thick, and have thickness not less than the projection beyond the column base; wider spacing or heavier loads require adjusted or engineered sizes.
OBC Division B, Subsection 9.15.3.

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

What this means in practice

A column collects half the beam span on each side, so spacing the posts farther apart than the tabulated assumption means the footing area must grow proportionally. Practical pitfalls: pads poured thin and unreinforced under heavy point loads, footings cast on disturbed trench backfill near the sump or plumbing runs, and finished-basement renovations that move a post onto plain slab, since a 75 mm slab is not a footing. Interior column footings in a heated basement do not need frost depth, but columns for decks and porches outside do.

Plain language

Each basement post needs its own concrete pad below the floor, sized to the weight it carries, roughly 0.4 to 1.0 square metres depending on how many floors sit above. The basement slab itself is not strong enough to act as that pad.

Related questions

What are the requirements for steel and wood columns in a basement 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.