The Ontario Building Code | Dimensions for Rectangular Runs and Treads

9.8.4.2. Dimensions for Rectangular Runs and Treads

(1) The run, which is measured as the horizontal nosing-to-nosing distance, and the tread depth of rectangular treads shall conform to Table 9.8.4.1.

(2) The depth of a rectangular tread shall be not less than its run and not more than its run plus 25 mm.