The Ontario Building Code | Curved Stairs
220.127.116.11. Curved Stairs
(1) Except as permitted by Sentence (2), tapered treads shall not be used in an exit.
(2) A curved stair used as an exit shall have,
(a) a handrail on each side,
(b) treads with a minimum run of 240 mm exclusive of nosings,
(c) treads that conform to Article 18.104.22.168. where they are measured 230 mm away from the handrail at the narrow end of the tread, and
(d) an inside radius that is not less than twice the stair width.