The Ontario Building Code | Continuity of Firewalls
3.1.10.3. Continuity of Firewalls
(1) A firewall shall extend from the ground continuously through, or adjacent to, all storeysof a building or buildingsso separated, except that a firewall located above a basement storage garageconforming to Article 3.2.1.2. is permitted to commence at the floor assembly immediately above the storage garage.
(2) A firewall is permitted to terminate on the underside of a reinforced concrete roof slab provided,
(a) the roof slab on both sides of thefirewall has a fire-resistance rating not less than,
(i) 1 h if the firewall is required to have a fire-resistance rating not less than 2 h, or
(ii) 2 h if the firewall is required to have a fire-resistance rating not less than 4 h, and
(b) there are no concealed spaces within the roof slab in that portion immediately above the firewall.
In Plain Language
A firewall must run continuously from the ground through (or alongside) every storey of the buildings it separates, though one can start above a basement storage garage under specific conditions, and can terminate at the underside of a suitably rated reinforced concrete roof slab.
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.