The Ontario Building Code | Parapets
3.1.10.4. Parapets
(1) Except as permitted by Sentences (2) and 3.1.10.3.(2), a firewall shall extend above the roof surface to form a parapet not less than,
(a) 150 mm high for a firewall required to have a fire-resistance rating not less than 2 h, and
(b) 900 mm high for a firewall required to have a fire-resistance rating not less than 4 h.
(2) A firewall that separates two buildings with roofs at different elevations need not extend above the upper roof surface to form a parapet, provided the difference in elevation between the roofs is more than 3 m.
In Plain Language
Firewalls must extend above the roof to form a parapet, 150 mm high for a 2-hour-rated firewall or 900 mm for a 4-hour-rated one, except where roofs on either side differ in elevation by more than 3 m.
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.