The Ontario Building Code | Dimensions for Angled Treads
9.8.4.3. Dimensions for Angled Treads
(1) Angled treads in required exit stairs shall conform to the requirements in Article 3.4.6.9.
(2) Except as provided in Article 9.8.4.5., angled treads in other than required exit stairs shall have an average run, which is measured as the horizontal nosing-to-nosing distance, of not less than 200 mm and a minimum run of 150 mm.
(3) The depth of an angled tread shall be not less than its run, measured as the horizontal nosing-to-nosing distance, at any point and not more than its run at any point plus 25 mm.
In Plain Language
Angled treads, used on curved or winding stairs, have their own dimensional requirements set out in this article, since their shape varies across the width of the 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.