What load must stairs in an Ottawa house be built for?

For stairs serving a single dwelling unit, clause 9.8.9.1.(1)(a) of the 2024 Ontario Building Code (O. Reg. 163/24) sets the design load at 1.9 kPa.

For a private stair within a dwelling unit, the Part 9 prescriptive rules give the carpenter the member sizes that satisfy the Code without a full structural calculation, provided the stair stays within the limits of those tables. Wood stringers must have an effective depth of at least 90 mm, an overall depth of at least 235 mm, and be spaced not more than 900 mm apart. Treads must be at least 25 mm thick.

Where a stair falls outside the Part 9 prescriptive limits, the framing is designed to Part 4, which means a qualified, registered designer (BCIN), an engineer or an architect, or you for a house you own, works out the loads and sizes. The same applies if you are asking about a stair that carries an unusually long span, uses non-standard materials or serves a configuration the tables do not cover. For anything outside the standard prescriptive path, ask the City of Ottawa (Building Code Services) what it will accept before work begins.

When you receive a quote for a stair rebuild or new stair, ask to see each of these lines itemised: design (where the stair falls outside the prescriptive tables), the building permit, materials, labour, patching and finishing, and disposal.