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OBC DIVISION B · PART 9 · SECTION 9.20 — MASONRY AND ICF WALLS NOT IN CONTACT WITH THE GROUND

How thick do above-grade masonry walls have to be in Ontario?

Above-grade loadbearing masonry walls in Part 9 buildings are generally at least 190 mm (nominal 8 in.) thick, with 140 mm (nominal 6 in.) permitted in limited low-rise cases. Masonry veneer is non-structural and must be at least about 70 mm (nominal 3 in.) thick.

Code reference
The OBC sets minimum thicknesses for masonry walls above ground based on their role: loadbearing solid or hollow-unit walls must meet minimum unit thicknesses tied to wall height and the loads supported, cavity walls have minimum wythe thicknesses, and non-loadbearing veneer has a smaller minimum thickness since it carries only its own weight and transfers lateral loads through ties.
OBC Division B, Subsection 9.20.6.

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

What this means in practice

Most modern Ontario houses use masonry only as veneer over wood framing, where the roughly 70 mm minimum and the tie, cavity and support rules govern. True loadbearing masonry, block garages, party walls, older-style solid brick, invokes the thicker minimums plus height-to-thickness limits, lateral support requirements at floors and roof, and bonding rules between wythes. Renovators altering solid-masonry century homes should be careful: removing an interior wythe or cutting large openings changes a wall that was designed by thickness rules, and usually requires engineered lintels and assessment rather than Part 9 tables.

Plain language

If brick or block actually holds the building up, the wall generally needs to be at least 190 mm thick, sometimes 140 mm for small single-storey cases. The thin brick skin on most modern houses is just a facing about 70 mm or more thick, with the wood wall doing the structural work.

Related questions

How must brick veneer be supported and tied to a house in Ontario?What are the Ontario Building Code rules for above-grade ICF walls in houses?

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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.