The Ontario Building Code | Minimum Size of Building Drains and Sewers
7.4.9.4. Minimum Size of building Drains and Sewers
(1) Every sanitary building drain and every sanitary building sewer shall be at least 4 in. in size.
(2) Every storm building drain and every storm building sewer shall be at least 4 in. in size.
7.4.10. Hydraulic Loads
In Plain Language
Every sanitary and storm building drain and sewer has a minimum required size set out in this article, ensuring the main drainage runs can handle the combined flow from everything connected to them.
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.