What counts as a storey and building height under Part 9 in Ontario?
Building height in Part 9 is counted in storeys above the first storey, which is the uppermost storey with its floor not more than 2 m (6 ft 7 in) above grade. Basements below that generally don't count.
Paraphrased for clarity — open this provision in the BUILDAiD Library for the exact wording.
This measurement decides whether you stay within Part 9's 3-storey limit, so it matters on sloped lots and walkout basements. A lower level with its floor more than 2 m above grade on one side can become a storey, potentially pushing a 'three-storey' house into Part 3 territory. Mezzanines below certain area thresholds are excluded from the storey count. Establish grade and floor elevations on your site plan before finalizing the design, since a small elevation change can reclassify the whole building.
The code counts floors, not metres. Your basement usually doesn't count as a storey, but on a sloped lot a walkout level might. That count decides whether the simpler house rules still apply to your project.
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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.