The Ontario Building Code | Serving Water Closets
7.4.9.2. Serving water Closets
(1) The size of every drainage pipe that serves a water closet shall be at least 3 in.
(2) The size of every horizontal drainage pipe downstream of the third water closet fixture drainconnection shall be at least 4 in.
(3) The size of every soilstack that serves more than six water closets shall be at least 4 in.
(4) The size of the discharge pipe serving a macerating toilet system shall be at least ¾ in.
(5) No vertical leg of the drainage pipe from a water closet or other fixture that has an integral siphonic flushing action shall exceed 1 000 mm.
In Plain Language
Every drainage pipe serving a water closet must be at least 3 in. in size, and this article also sets minimum sizes for the horizontal drain sections serving multiple water closets.
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.