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OBC DIVISION B · PART 3 · SECTION 3.2 — FUNCTIONAL STATEMENTS / BUILDING FIRE SAFETY

How does spatial separation limit windows near property lines in Ontario?

The area of unprotected openings, mainly windows and doors, in an exterior wall is capped based on limiting distance to the property line, wall area and occupancy, and the wall itself may need a fire-resistance rating and noncombustible cladding.

Code reference
Each exposing building face is assessed against its limiting distance, measured to the property line or an assumed line between buildings. Tables set the maximum percentage of unprotected openings by distance, wall area and occupancy hazard, with sprinklered buildings receiving credit, and prescribe the required rating, construction and cladding of the wall as the permitted opening percentage drops.
OBC Division B, Subsection 3.2.3.

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

What this means in practice

Spatial separation regularly drives elevation design on tight urban sites: window percentages shrink quickly inside about 3 m of a lot line, and at very short limiting distances openings may be prohibited entirely. Remember to check both real property lines and assumed lines between buildings on the same lot, and that glazing percentage calculations use compartment-by-compartment exposing faces. Firewalls or upgraded rated walls with wired glass or fire shutters are common fixes when the numbers do not work.

Plain language

The closer a wall sits to the property line, the fewer windows it may have, so a fire cannot easily jump to the neighbour. Very close walls may need fire-rated construction with little or no glass at all.

Related questions

When is noncombustible construction required under the Ontario Building Code?When are automatic sprinklers required in a building in Ontario?What are the fire department access route requirements 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.