The Ontario Building Code | Fire Blocks between Nailing and Supporting Elements
3.1.11.3. Fire Blocks between Nailing and supporting Elements
(1) In a building required to be of noncombustible construction, a concealed space in which there is an exposed ceiling finish with a flame-spread rating more than 25, shall be provided with fire blocks conforming to Article 3.1.11.7. between wood nailing elements, so that the maximum area of the concealed space is not more than 2 m2.
(2) In a building required to be of noncombustible construction, fire blocks conforming to Article 3.1.11.7. shall be provided in the concealed spaces created by the wood members permitted by Sentence 3.1.5.8.(2), so that the maximum area of a concealed space is not more than 10 m2.
In Plain Language
In noncombustible-construction buildings with exposed ceiling finishes above a 25 flame-spread rating, fire blocks must limit concealed spaces between wood nailing elements to no more than 2 m², and similar blocking limits apply (10 m² cap) to concealed spaces created by the wood members allowed under Sentence 3.1.5.8.(2).
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.