How big an air space goes behind brick veneer in Ontario?

The Ontario Building Code (O. Reg. 163/24, s. 9.20.6.4) sets 25 mm as the minimum air space behind masonry veneer over a wood-frame wall. We found no maximum in the Code.

That minimum is a floor, not a target. The actual gap on a given project depends on the thickness of the veneer unit, the wall assembly, the flashing and weep-hole layout, and how the ties are installed. The Code (s. 9.20.9.5) requires corrosion-resistant straps not less than 0.76 mm thick and 22 mm wide, at maximum spacings of 400 mm vertical by 800 mm horizontal, 500 mm vertical by 600 mm horizontal, or 600 mm vertical by 400 mm horizontal. Throughwall flashing is required so that any moisture collecting in the air space is directed to the exterior (s. 9.20.13.3), and weep holes are required at the bottom of the cavity, spaced not more than 800 mm apart (s. 9.20.13.8.(1)).

Veneer units themselves must be not less than 70 mm thick (s. 9.20.6.4). For slab or panel facings of natural or artificial stone, the Code points to Subsection 4.3.2, which is a design provision; if you are looking at thin or panel stone rather than full-unit brick, ask the City how that system is assessed.

On a repair or re-cladding job, the mason will need to confirm what is behind the existing veneer before specifying the new assembly. If the work involves rebuilding a section or altering an opening, that may be construction under the Building Code Act; the City can say whether a permit is needed.

If you are getting quotes, ask each contractor to note the air-space dimension, tie spacing, flashing termination points and weep-hole spacing in writing, along with where the veneer units come from and how joints will be finished.