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OBC DIVISION B · PART 3 · SECTION 3.1 — APPLICATION

How are building height and building area determined under the Ontario Building Code?

Building height is the number of storeys between the first storey and the roof, with the first storey established relative to grade. Building area is the greatest horizontal area above grade within exterior walls, measured per storey.

Code reference
Building height in storeys counts from the first storey upward, where the first storey is the one with its floor closest to and not more than a set distance above grade. Building area is the largest horizontal area of the building above grade, measured to the outside of exterior walls or the centreline of firewalls.
OBC Division A, Article 1.4.1.2.

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

What this means in practice

These two defined terms feed directly into the 3.2.2 construction and sprinkler articles, so small measurement decisions can change permitted construction type. Grade itself is a defined, averaged elevation, and a walkout basement can count as a storey if it sits too high relative to grade. Firewalls can divide a structure into separate buildings for area purposes, which is a common strategy to stay within noncombustible or sprinkler thresholds.

Plain language

The Code measures a building by how many floor levels sit above ground and by its biggest footprint. Those numbers decide which fire safety rules apply, and even a partly buried basement can count as a storey if it pokes up too far.

Related questions

Which buildings fall under Part 3 of the Ontario Building Code?How is major occupancy classified under the Ontario Building Code?What is a high building 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.