9.8.9.4.Wooden Stair Stringers

(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. in stairs serving not more than one dwelling unit or a house with a secondary suite including their common spaces, and 600 mm o.c. in other stairs. (2) For stairs serving not more than one dwelling unit or a house with a secondary suite including their common spaces, where risers support the front portion of the tread, the space between stringers shall be not more than 1 200 mm.