Spiral staircase up to a loft in my Ottawa home, allowed?

Spiral stairs are allowed inside a house under the 2024 Ontario Building Code (O. Reg. 163/24), but clause 9.8.4.7. gives them their own numbers in place of the usual private-stair table.

For a spiral stair, 9.8.4.7.(1) sets a clear width of at least 660 mm, risers of not more than 240 mm, treads at least 190 mm deep measured 300 mm from the centre line, headroom of at least 1 980 mm, and handrails on both sides, with the outer one at least 1 070 mm high. Under 9.8.4.7.(2), a spiral stair can serve as the only way out for not more than 3 persons.

The loft itself still needs a guard where the drop is more than 600 mm (9.8.8.1.), at least 900 mm high inside a dwelling unit (9.8.8.3.(2)), with openings that stop a 100 mm sphere (9.8.8.5.).

Because a new interior stair does not appear on either the City of Ottawa's permit-required list or its exempt list, the right step is to ask Building Code Services at ottawa.ca whether your specific project needs a permit before work starts. If your home is individually designated under the Ontario Heritage Act, contact City heritage staff first as well, since building-permit exemptions do not apply to designated properties.

Before you commit, ask the carpenter to show you exactly which clause of 9.8.4.7. governs the tread geometry they are proposing, and how the guard at the loft opening will meet the 900 mm height and sphere requirements.