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.
In Plain Language
Rectangular stair runs and treads (the horizontal part you step on) must meet the dimensions set out in this article, working together with riser height to create a safe, comfortable stair.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.