The Ontario Building Code | Required Fire Blocks in Wall Assemblies
18.104.22.168. Required Fire Blocks in wall Assemblies
(1) Except as permitted in Sentence (2), fire blocks shall be provided to block off concealed spaces within wall assemblies, including spaces created by furring,
(a) at each floor level,
(2) Fire blocks required in Sentence (1) need not be provided, if,
(a) the insulated wall assembly contains not more than one concealed air space and the horizontal thickness of that air space is not more than 25 mm,
(b) the exposed construction materials within the space are noncombustible, or
(c) the exposed construction materials within the space, including insulationhttp://thehandyforce.com/insulation/" title ="Toronto home insulation">insulation, but not including wiring, piping or similar services, have a flame-spread ratingof not more than 25.