9.8.4.4.Uniformity and Tolerances for Risers, Runs 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) Rectangular treads 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. (4) Tapered treads in a flight shall have a uniform run in accordance with the construction tolerances stipulated in Sentence (3) when measured at a point 300 mm from the centre line of the handrail as described in Sentence 9.8.7.1.(5). (5) The slope of treads shall not exceed 1 in 50.