The Ontario Building Code | Vent Requirements
9.19.1.2. vent Requirements
(1) Except as provided in Sentence (2), the unobstructed vent area shall be not less than 1/300 of the insulated ceiling area.
(2) Where the roof slope is less than 1 in 6 or in roofs that are constructed with roof joists, the unobstructed vent area shall be not less than 1/150 of the insulated ceiling area.
(3) Required vents are permitted to be roof type, eave type, gable-end type or any combination of them, and shall be distributed,
(a) uniformly on opposite sides of thebuilding,
(b) with not less than 25% of the required openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings located at the top of the space, and
(c) with not less than 25% of the required openings="http://thehandyforce.com/windows/" title ="Window installer in Toronto">openings located at the bottom of the space.
(4) Except where each roof joist space referred to in Sentence (2) is separately vented, roof joist spaces shall be interconnected by installing purlins not less than 38 mm by 38 mm on the top of the roof joists.
(5) vents shall comply with CAN3-A93-M, "Natural Airflow ventilators for Buildings".
In Plain Language
Roof space vents must meet specific requirements set out in this article, covering their sizing, type, and placement for effective ventilation.
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.