The Ontario Building Code | Treads and Risers
220.127.116.11. Treads and Risers
(1) Except as permitted for dwelling unitsand by Sentence 18.104.22.168.(1) for fire escapes, steps for stairs shall have a run of not less than 255 mm and not more than 355 mm between successive steps.
(2) Steps for stairs referred to in Sentence (1) shall have a rise between successive treads not less than 125 mm and not more than 200 mm.
(3) Except in fire escape stairs and where an exterior stair adjoins a walkway as permitted by Sentence 22.214.171.124.(3), risers, measured as the vertical nosing-to-nosing distance, shall be of uniform height in any one flight, with a maximum tolerance of,
(a) 5 mm between adjacent treads or landings, and
(b) 10 mm between the tallest and shortest risers in a flight.
(4) Except in fire escape stairs, treads, measured as the horizontal nosing-to-nosing distance, shall have a uniform run with a maximum tolerance of,
(a) 5 mm between adjacent treads, and
(b) 10 mm between the deepest and shallowest treads in a flight.
(5) Treads and risers shall not differ significantly in run and rise in successive flights in any stair system.
(6) Where angled treads are incorporated into a stair, the treads in all sets of angled treads within a flight shall turn in the same direction.
(7) The slope on treads or landings shall not exceed 1 in 50.
(8) Except as permitted by Sentence (10), the top of the nosing of a stair tread shall have a rounded or bevelled edge extending not less than 6 mm and not more than 13 mm measured horizontally from the front of the nosing.
(9) The front edge of stair treads in exitsand public access to exits shall be at right angles to the direction of exit travel.
(10) If resilient material is used to cover the nosing of a stair tread, the minimum radius or bevel required by Sentence (8) is permitted to be reduced to 3 mm.