The Ontario Building Code | Underground Walkway
3.2.3.20. Underground Walkway
(1) An underground walkway shall not be designed or used for any purpose other than pedestrian travel unless,
(a) the purpose is permitted, and
(b) sprinklers are installed in any space in the walkway containing an occupancy.
(2) buildingsconnected by an underground walkway shall be separated from the walkway by a fire separation with a fire-resistance rating not less than 1 h.
(3) An underground walkway shall be of noncombustible construction suitable for an underground location.
(4) In an underground walkway,
(a) smoke barrier doors shall be installed at intervals of not more than 100 m, or
(b) the travel distance from the door of an adjacent room or space to the nearest exitshall be not more than one and a half times the least allowable travel distance to an exit for any of the adjacent occupancies as permitted by Sentence 3.4.2.5.(1).
(5) An underground walkway between buildings shall be not more than 9 m wide.
In Plain Language
This clause addresses how attached garages, sheds, and other accessory structures on a residential property factor into the spatial separation requirements of the main dwelling, since these structures can be treated somewhat differently than the main 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.