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OBC DIVISION B · PART 9 · SECTION 9.25 — HEAT TRANSFER, AIR LEAKAGE AND CONDENSATION CONTROL

What are the attic insulation rules for houses in Ontario?

Attic insulation must be installed at the levels set by SB-12, commonly around RSI 10.6 (R-60) for new houses, without blocking eave ventilation: baffles must preserve a clear vent space, roughly 63 mm (2.5 in.), between insulation and roof sheathing, and loose-fill has slope and containment limits.

Code reference
Ceiling insulation below ventilated attics must achieve the effective thermal resistance required by Ontario's energy efficiency compliance packages, be installed evenly to full depth including over the wall plates where geometry allows, maintain the required clearance for eave ventilation using baffles or equivalent, and respect restrictions on loose-fill insulation on sloped surfaces and around heat sources and access hatches.
OBC Division B, Subsection 9.25.2. and SB-12

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

What this means in practice

The perennial attic conflict is depth versus ventilation at the eaves: R-60 loose-fill wants roughly 400 mm of depth, which buries standard heel heights, so raised-heel trusses or rigid baffles at every rafter bay are the working solutions. Mark settled depth with rulers for inspection, insulate and weatherstrip the hatch, and dam around chimneys and non-IC pot lights. Air sealing the ceiling plane before blowing insulation matters more than the last R-10, since attic bypasses around plumbing stacks, pot lights and partition tops drive the ice damming and frost that homeowners later blame on insulation.

Plain language

New Ontario attics typically get about R-60 of insulation, roughly 400 mm of fluffy fill spread evenly. The trick is doing it without smothering the soffit vents, so plastic or foam baffles keep a clear air channel at the edges, and the attic hatch gets its own insulation blanket.

Related questions

What are the insulation installation requirements in the Ontario Building Code?Does polyethylene have to go on the warm side of the wall 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.