The Ontario Building Code | Traps for Storm Drainage Systems
7.4.5.2. Traps for Storm drainage Systems
(1) Where a storm drainage system is connected to a public combined sewer, a trap shall be installed between any opening in the system and the drain or sewer, except that no trap is required if the opening is the upper end of a leader that terminates,
(a) at a roof that is used only for weather protection,
(b) not less than 1 000 mm above or not less than 3.5 m in any other direction from any air inlet, openable window or door, and
(c) not less than 1 800 mm from a property line.
In Plain Language
Where a storm drainage system connects to a combined sewer, it requires a trap, since combined sewers can carry sewage gas that must be blocked from entering the storm system and the building.
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.