The Ontario Building Code | Uniformity and Tolerances for Risers and Treads
220.127.116.11. Uniformity and Tolerances for Risers and Treads
(1) Except as provided in Sentence (2), risers 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.
(2) Except for required exit stairs, where the top or bottom riser in a stair adjoins a sloping finished walking surface such as a garage floor, driveway or sidewalk, the height of the riser across the stair shall vary by not more than 1 in 12.
(3) Treads shall have 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.
(4) Where angled treads or winders are incorporated into a stair, the treads in all sets of angled treads or winders within a flight shall turn in the same direction.
(5) The slope of treads shall not exceed 1 in 50.