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OBC DIVISION B · PART 3 · SECTION 3.4 — EXITS

What fire separation is required around exits in Ontario?

Every exit must be separated from the rest of the building by fire separations with a fire-resistance rating at least equal to that required for the floor assemblies it serves, and not less than 45 minutes, commonly 1 h to 2 h in taller buildings.

Code reference
Exit enclosures, including stair shafts and exit passageways, must be constructed as fire separations rated to match the highest rating required for the floor assemblies through which they pass, with a minimum rating, and openings limited to those serving the exit, protected by rated closures with self-closing hardware.
OBC Division B, Subsection 3.4.4.

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

What this means in practice

The exit enclosure is the protected tube occupants rely on, so the Code sharply restricts what may open into it: service rooms, storage and most ancillary spaces cannot connect directly to an exit stair. Watch penetrations, since ducts and conduits through stair shafts are tightly controlled and must be fire stopped. Rooms under exit stairs and combustible materials within the enclosure are recurring inspection failures, as are unrated vision panels and non-labelled doors.

Plain language

Exit stairs are wrapped in fire-rated walls and doors, like a protected tunnel through the building, so once you step inside you can walk down safely even while the fire burns on the floors around you.

Related questions

When are two exits required from a floor area in Ontario?How is required exit width calculated under the Ontario Building Code?How many exits does a floor area need under the Ontario Building Code?

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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.