What is the minimum ceiling height in Ontario?
Rooms in dwelling units generally require a ceiling height of at least 2.3 m over the required floor area, with lower allowances for basements and under beams. Rooms with sloped ceilings can use a portion of the room at full height.
The percentage structure exists to make rooms with sloped ceilings and finished basements workable: the code fixes a full-height zone over part of the required floor area and a minimum clear height everywhere else that counts toward the required area — space below the minimum height simply does not count as required floor area. Basement rules are more permissive than above-grade rooms, with additional relaxations for existing basements being converted to living space under the renovation provisions (and further reduced heights permitted for second units in existing houses). Measure from finished floor to the underside of the finished ceiling, and check beams, ducts and stair headroom separately — they have their own limits.
Most rooms need about 7'7" of ceiling. Basements get a break — roughly 6'11" — and older-home basement apartments get even more forgiveness. Sloped ceilings are fine as long as enough of the room is full height. The number that surprises people is how low the code lets a legal basement ceiling be.
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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.