The Ontario Building Code | Required Fire Blocks in Concealed Spaces
9.10.16.1. Required Fire Blocks in Concealed Spaces
(1) Concealed spaces in interior walls, ceilings, floors and crawl spaces shall be separated by fire blocks from concealed spaces in exterior walls and attic or roof spaces.
(2) Fire blocks shall be provided at all interconnections between concealed vertical and horizontal spaces in interior coved ceilings, drop ceilings and soffits where the exposed construction materials within the concealed spaces have a surface flame-spread ratinggreater than 25.
(3) Fire blocks shall be provided at the top and bottom of each run of stairs where they pass through a floor containing concealed space in which the exposed construction materials within the space have a surface flame-spread rating greater than 25.
(4) In unsprinklered buildings of combustible construction, every concealed space created by a ceiling, roof space or unoccupied attic space shall be separated by fire blocksinto compartments of not more than 300 m² in area where such space contains exposed construction materials having a surface flame-spread rating greater than 25.
(5) No dimension of the concealed space described in Sentence (4) shall exceed 20 m.
(6) Concealed spaces in mansard or gambrel style roofs, exterior cornices, balconies and canopies of combustible construction in which the exposed construction materials within the space have a surface flame-spread rating exceeding 25 shall have vertical fire blocks at intervals of not more than 20 m and at points where such concealed spaces extend across the ends of required vertical fire separations.
In Plain Language
Fire blocks are required in concealed spaces at the locations set out in this article, stopping fire and smoke from silently spreading through hidden voids like those above ceilings or within floor assemblies.
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.