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OBC DIVISION B · PART 9 · SECTION 9.18 — CRAWL SPACES

What is the difference between a heated and unheated crawl space under the Ontario Building Code?

A heated crawl space is treated like a short basement: perimeter walls insulated with air and vapour barriers, conditioned air supplied, no venting to outside, sealed ground cover. An unheated crawl space is outside the envelope: it must be vented, and the floor above it insulated and sealed.

Code reference
The OBC distinguishes crawl spaces by whether they are heated. Heated crawl spaces are treated as basements for insulation, air leakage and moisture control, with the thermal envelope at the perimeter walls and ventilation to outside omitted in favour of conditioning. Unheated crawl spaces require outdoor ventilation and ground cover, with the insulated, air-sealed envelope located in the floor assembly above.
OBC Division B, Section 9.18.

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

What this means in practice

Choosing the boundary is the key design decision. Heated crawl spaces are usually the better performer in Ontario: ducts and plumbing stay inside the envelope, freeze risk drops, and insulating short perimeter walls is simpler than insulating a floor full of penetrations. Unheated crawl spaces demand disciplined floor insulation, an air barrier at the subfloor, and protection of every pipe. The classic failure is a hybrid, a vented crawl space with heating ducts running through it, which wastes energy and drives condensation. Whichever model is chosen, document it consistently for inspection.

Plain language

If the crawl space is heated, treat it like a mini basement: insulate its walls, seal it up, and let house air condition it. If it is unheated, it belongs to the outdoors: vent it, cover the ground, and insulate the floor above it, including any pipes.

Related questions

What are the ventilation and access requirements for crawl spaces 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.