What is the Ontario Building Code requirement for deck stair width?

The Ontario Building Code sets specific minimum dimensions for deck stairs that every Ottawa homeowner should know before building or replacing exterior steps. Getting stair width wrong can trigger a failed inspection and require costly rework, so understanding the requirements upfront saves both money and frustration.

For residential deck stairs serving a single dwelling, the Ontario Building Code (OBC Section 9.8) requires a minimum clear width of 860 millimetres, which is just under 34 inches. This measurement is taken between the inside faces of the stair stringers or guards—not the outside dimensions of the staircase. If your guards or handrails project inward, the clear walking width must still meet that 860 mm minimum after accounting for any projections.

In practice, most Ottawa deck builders frame stairs at 36 inches wide or wider. The code minimum of 860 mm feels narrow when you're carrying anything—groceries, coolers for a backyard gathering, or furniture. A 42-inch to 48-inch wide staircase is more comfortable and looks proportional on most decks. If your deck is a primary entry point to the backyard, wider stairs also improve traffic flow during entertaining.

Stair dimensions go beyond just width. The OBC specifies that risers (the vertical face of each step) must be between 125 mm and 200 mm in height, with a maximum variance of 6 mm between the tallest and shortest riser in the same staircase. Treads (the horizontal surface you step on) must provide a minimum run of 210 mm with a going (horizontal distance from nose to nose) of at least 210 mm. The consistency requirement is important—uneven risers are a leading cause of stair falls, and inspectors measure every one.

Nosing is another detail the code addresses. If your stair treads have a projecting nose that overhangs the riser, the nosing projection must be between 13 mm and 25 mm. Alternatively, you can use a sloped riser with an angle of 60 degrees or more from horizontal, which eliminates the nosing requirement. Many composite decking stairs use this approach with solid riser boards installed at a slight angle.

Handrails are required on at least one side of any staircase with more than two risers (meaning three or more steps from top to bottom). The handrail must be between 865 mm and 965 mm in height, measured vertically from the stair nosing. The graspable portion must be shaped so a hand can wrap around it—flat-top deck rail caps don't qualify as handrails on stairs. A separate round or contoured handrail, typically 32 to 38 mm in diameter, mounted inside the guard rail system meets this requirement.

For stairs more than 1,100 mm wide, handrails are required on both sides. This threshold comes up more often than you'd expect with grand-style deck staircases or wide landings leading to patios.

Ottawa building inspectors check stair dimensions carefully during the framing and final inspections. If you're planning a deck project that includes stairs, working with an Ottawa contractor who builds to code from the start avoids the cost and delay of corrections after an inspector flags non-compliant framing.

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