The Ontario Building Code | Exhaust Duct Negative Pressure
3.6.3.4. Exhaust Duct Negative pressure
(1) If a vertical service space contains an exhaust duct that serves more than one fire compartment, the duct shall have a fan located at or near the exhaust outlet to ensure that the duct is under negative pressure.
3.6.4. Horizontal service Spaces and service Facilities
In Plain Language
Where a vertical service space contains an exhaust duct serving more than one fire compartment, the duct needs a fan near the outlet keeping the duct under negative pressure, so smoke is drawn out rather than pushed into other compartments.
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.