1. 1) Concealed spaces in interior wall, ceiling and crawl spaces shall be separated from concealed spaces in exterior walls and attic or roof spaces by fire blocks conforming to Article 3.1.11.7.

1. Except as permitted by Sentence (2), fire blocks conforming to Article 3.1.11.7. shall be provided to block off concealed spaces within a wall assembly
   1. at every floor level,
   2. at every ceiling level where the ceiling forms part of an assembly required to have a fire-resistance rating, and
   3. so that the maximum horizontal dimension is not more than 20 m and the maximum vertical dimension is not more than 3 m.
2. Fire blocks conforming to Sentence (1) are not required, provided
   1. the wall space is filled with insulation,
   2. the exposed construction materials and any insulation within the wall space are noncombustible,
   3. the exposed materials within the space, including insulation but not including wiring, piping or similar services, have a flame-spread rating not more than 25 on any exposed surface, or on any surface that would be exposed by cutting through the material in any direction, and fire blocks are installed so that the vertical distance between them is not more than 10 m, or
   4. 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.

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 3.1.5.10.(2) so that the maximum area of a concealed space is not more than 10 m2.

1. Fire blocks conforming to Article 3.1.11.7. shall be provided
   1. at all interconnections between concealed vertical and horizontal spaces in interior coved ceilings, drop ceilings and soffits in which the exposed construction materials within the space have a flame-spread rating more than 25, and
   2. at the end of each run and at each floor level in concealed spaces between stair stringers in which the exposed construction materials within the space have a flame-spread rating more than 25.

3.1.11.5. Fire Blocks in Horizontal Concealed Spaces

1. Except for crawl spaces conforming to Sentence 3.1.11.6.(1) and as required in Sentence (3), horizontal concealed spaces within a floor assembly or roof assembly of combustible construction, in which sprinklers are not installed, shall be separated by construction conforming to Article 3.1.11.7. into compartments
   1. not more than 600 m2 in area with no dimension more than 60 m if the exposed construction materials within the space have a flame-spread rating not more than 25, and
   2. not more than 300 m2 in area with no dimension more than 20 m if the exposed construction materials within the space have a flame-spread rating more than 25. (See Note A-3.1.11.5.(1).)
2. A concealed space in an exterior cornice, a mansard-style roof, a balcony or a canopy in which exposed construction materials within the space have a flame-spread rating more than 25, shall be separated by construction conforming to Article 3.1.11.7.
   1. at locations where the concealed space extends across the ends of required vertical fire separations, and
   2. so that the maximum dimension in the concealed space is not more than 20 m.
3. Except as provided in Sentence (4), in buildings conforming to Article 3.2.2.50. or 3.2.2.58., horizontal concealed spaces within a floor assembly or roof assembly of combustible construction shall be separated by construction conforming to Article 3.1.11.7. into compartments that are
   1. not more than 600 m2 in area with no dimension more than 60 m, if the exposed construction materials within the space have a flame-spread rating not more than 25, and
   2. not more than 300 m2 in area with no dimension more than 20 m, if the exposed construction materials within the space have a flame-spread rating more than 25. (See Note A-3.1.11.5.(3).) 4) Fire blocks conforming to Sentence (3) are not required where the horizontal concealed space within the floor or roof assembly is entirely filled with noncombustible insulation such that any air gap between the top of the insulation and the floor or roof deck does not exceed 50 mm.

1. A crawl space that is not considered as a basement by Article 3.2.2.9. and in which sprinklers are not installed, shall be separated by construction conforming to Article 3.1.11.7. into compartments not more than 600 m2 in area with no dimension more than 30 m.

1. Except as permitted by Sentences (2) to (4) and (7), fire blocks shall remain in place and prevent the passage of flames for not less than 15 min when subjected to the standard fire exposure in CAN/ULC-S101, "Fire Endurance Tests of Building Construction and Materials."
2. Gypsum board not less than 12.7 mm thick and sheet steel not less than 0.38 mm thick need not be tested in conformance with Sentence (1), provided all joints have continuous support.
3. In a building required to be of noncombustible construction, wood nailing elements described in Article 3.1.5.8. need not be tested in conformance with Sentence (1).
4. In a building permitted to be of combustible construction, in a combustible roof system permitted by Sentence 3.1.5.3.(2), and in a raised platform permitted by Sentence 3.1.5.10.(2), fire blocks are permitted to be
   1. solid lumber or a structural composite lumber product conforming to ASTM D 5456, "Evaluation of Structural Composite Lumber Products," not less than 38 mm thick,
   2. phenolic bonded plywood, waferboard, or oriented strandboard not less than 12.5 mm thick with joints supported, or
   3. two thicknesses of lumber or a structural composite lumber product conforming to ASTM D 5456, "Evaluation of Structural Composite Lumber Products," each not less than 19 mm thick with joints staggered, where the width or height of the concealed space requires more than one piece of lumber or structural composite lumber product not less than 38 mm thick to block off the space.
5. Openings through materials referred to in Sentences (1) to (4) shall be protected to maintain the integrity of the construction.
6. Where materials referred to in Sentences (1) to (4) are penetrated by construction elements or by service equipment, a fire stop shall be used to seal the penetration. (See Note A-3.1.11.7.(6).)
7. In buildings permitted to be of combustible construction, semi-rigid fibre insulation board produced from glass, rock or slag is permitted to be used to block the vertical space in a double stud wall assembly formed at the intersection of the floor assembly and the walls, provided the width of the vertical space does not exceed 25 mm and the insulation board
   1. has a density not less than 45 kg/m3,
   2. is securely fastened to one set of studs,
   3. extends from below the bottom of the top plates in the lower storey to above the top of the bottom plate in the upper storey, and
   4. completely fills the portion of the vertical space between the headers and between the wall plates.
      (See Note A-3.1.11.7.(7).)