9.8.9.1 — Loads on Stairs and Ramps

(1) Wooden stair stringers shall, (a) have a minimum effective depth of 90 mm, measured perpendicularly to the bottom of the stringer at the point of minimum cross-section, and an overall depth of not less than 235 mm, (b) be supported and secured top and bottom, (c) be not less than 25 mm actual thickness if supported along their length and 38 mm actual thickness if unsupported along their length, and (d) except as permitted in Sentence (2), be spaced not more than 900 mm o.c. for stairs serving a house or an individual dwelling unit, and 600 mm o.c. in other stairs. (2) For stairs serving a house or an individual dwelling unit, where risers support the front portion of the tread, the space between stringers shall be not more than 1 200 mm.

(1) Stair treads of lumber, plywood or O-2 grade OSB within dwelling units shall be not less than 25 mm actual thickness, except that if open risers are used and the distance between stringers exceeds 750 mm, the treads shall be not less than 38 mm actual thickness. (2) Stair treads of plywood or OSB, that are not continuously supported by the riser shall have their face grain or direction of face orientation at right angles to the stringers.