The Ontario Building Code | Size Restriction
7.5.7.2. Size Restriction
(1) The size of a branch vent, stack vent, vent stack or header shall be not less than the size of the vent pipe to which it is connected.
(2) Every sanitary building drain shall terminate at its upstream end in a stack of at least 3 in. size.
(3) A stack referred to in Sentence (2) shall be a soil stack if one is available and may be a vent stackor waste stack that provides at least 3 in. stack vent and that goes to open airabove the roof, either directly or through a header.
In Plain Language
This article places a size restriction on certain vent pipes, ensuring the vent is large enough to do its job without being oversized for the drainage load it protects.
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.