(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 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 tolerances described in Sentence (3) when measured at a point 300 mm from the centre line of the inside handrail.
(5) The slope of treads shall not exceed 1 in 50.