Stair Width Requirements in Ontario
Last updated: June 2026
Minimum clear width for interior and exterior stairs in Part 9 residential construction.
Detailed explanation
Under the Ontario Building Code (OBC) Part 9, the minimum clear width of a stairway serving a single dwelling unit is typically 860 mm (34 inches). This measurement is taken between walls, guards, or other obstructions.
Stairs serving more than one dwelling unit or used as a required exit may need to be wider. Always confirm whether the stair is a principal entrance, a secondary exit, or a private stair within a single unit.
Handrails and guards may project into the required width, but the code specifies limits on how much they can reduce the clear path. Measure at the narrowest point along the run.
Ontario Building Code references
Ontario Building Code
Section 9.8.2. — Stairways
General requirements for stair construction.
Ontario Building Code
Section 9.8.3. — Stair width
Minimum clear width dimensions.
Examples
- A basement stair in a single-family home must provide at least 860 mm clear width.
- A shared exit stair in a duplex may require a wider clear width depending on occupant load.
Common mistakes
- Measuring width at the top landing only, not at the narrowest point of the run.
- Ignoring handrail projections when checking clear width.
- Assuming all stairs can be 860 mm without checking exit and occupancy requirements.
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