What is the ideal basement staircase width and rise for Ontario Building Code compliance?

The Ontario Building Code requires a minimum stair width of 860 millimetres (approximately 34 inches) measured between finished walls, a maximum riser height of 210 millimetres (about 8.25 inches), and a minimum tread depth of 220 millimetres (approximately 8.7 inches). These are the legal minimums, but experienced basement contractors in the GTA will tell you that going wider and more gradual makes the space feel dramatically more open and inviting.

The minimum 860 mm width is measured as the clear width between finished surfaces — so if you're adding drywall to the stairwell walls, measure after the drywall is up, not before. If you're installing a handrail on one side (which is required by code), the handrail can project up to 100 mm into that clear width. However, if you have handrails on both sides, each can project 100 mm, effectively requiring a rougher opening of about 1,060 mm (42 inches) to maintain the minimum clear width. For a finished basement that feels genuinely welcoming, many GTA contractors recommend framing the stairwell at 36 to 42 inches clear — it makes moving furniture downstairs far easier and eliminates the cramped tunnel feeling that plagues many older Toronto basement stairs.

Headroom is often the biggest challenge in GTA basement stair renovations, particularly in post-war bungalows across Scarborough, North York, and Etobicoke where ceiling heights are already tight. The Ontario Building Code requires a minimum headroom of 1,950 millimetres (6 feet 5 inches) measured vertically from the nose of any tread to the ceiling above. In many older homes, the existing stairs were built before current codes and may not meet this standard. If your stairwell headroom is tight, your contractor may need to lower the basement floor at the stair landing, reconfigure the stair layout with a turn or L-shape, or adjust the header opening in the main floor framing — all of which require structural consideration and a building permit.

Consistency in riser height is critically important for safety and is strictly enforced during inspections. The Ontario Building Code allows a maximum variation of only 6 millimetres between the tallest and shortest riser in any flight of stairs. Inconsistent risers are a leading cause of falls — your body develops a rhythm going up or down stairs, and even a small variation in one step can cause a stumble. A skilled contractor will calculate the total rise (floor to floor height) and divide it evenly across all risers to ensure perfect consistency. With typical GTA basement floor-to-floor heights of 8 to 9 feet, you'll have 13 to 16 risers.

Handrails and guards are equally important code requirements. You need a handrail on at least one side of the stairway, graspable with a cross-section that allows a proper grip (typically 32 to 43 mm diameter for round handrails). The handrail must be between 865 and 965 millimetres above the stair nosing. If one side of the stairway is open (not against a wall), you need a guard at least 900 millimetres high with balusters spaced so that a 100 mm sphere cannot pass through — this prevents small children from slipping through the openings.

If your existing basement stairs are steep, narrow, or don't meet current code, upgrading them is one of the best investments in your basement renovation. A new code-compliant staircase with proper width, consistent risers, and solid handrails costs $3,000–$8,000 depending on materials and configuration, and it transforms the entire feel of the finished basement. This work requires a building permit and inspection from the City of Toronto Building Division.