When do two areas count as a combination room?
Two areas are treated as a combination room when the opening between them is at least 40% of the wall area shared by the two spaces.
Conditions and exceptions
- Below that threshold each space is assessed on its own for area, light, and ventilation.
- The classification changes how required window area is calculated.
- Commonly decides whether a kitchen-and-living space is one room or two.
Where this comes from
National Building Code of Canada — Part 9
This page states the requirement and points you to the publisher. It does not reproduce the code text — read the provision itself at the official source below.
Read the official text at NRC — Codes Canada publications →Verify this against the code edition actually adopted where you are building. Provinces, territories, and municipalities amend on their own schedules, and where the governing document and this page disagree, the governing document controls. This is not legal, engineering, or permitting advice. Last reviewed 2026-08-12.
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