BCAB 1985 - Requirement for fire blocks in an exterior wall assembly

Requirement for fire blocks in an exterior wall assembly

Project Description

The project is the design and construction of a new house.

An exterior wall of the house contains a concealed air space between the sheathing membrane and the back of the metal cladding.  The space is created by two layers of 19 mm wood strapping; one layer is horizontal and one layer is vertical.  The space has a horizontal thickness of 38 mm, a vertical height of 4.2 m, and it is enclosed at the top and bottom with a metal flashing.

Applicable Code requirements (BCBC 2024)

Sentences 9.10.16.2.(1 and 2), Division B, 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,

(b) at each ceiling level where the ceiling contributes to part of the required fire-resistance rating, and

(c) at other locations within the wall, so that the distance between fire blocks does not exceed 20 m horizontally and 3 m vertically.

(2) Fire blocks described in Sentence (1) are not required, provided

(a) the insulated wall assembly contains not more than one concealed air space whose horizontal thickness is not more than 25 mm,

(b) the exposed construction materials within the space are noncombustible,

(c) the exposed construction materials within the space, including insulation, but not including wiring, piping or similar services, have a flame-spread rating of not more than 25, or

(d) the concealed wall space is filled with insulation.

Decision being appealed (Local Authority’s position)

The concealed space in the wall assembly exceeds 3 m vertically and none of the exceptions apply.  Therefore, a fire block is required in the concealed space.

Appellant's position

The proposed concealed space is isolated, limited in extent, non-continuous, terminated with a fire-resistive flashing, meets the life-safety intent of the Code, and can be accepted as an alternative solution.

Appeal Board Decision #1985

The Board confirms the decision of the local authority.

It is the determination of the Board that a fire block is required in the concealed space to limit the vertical dimension of the space to not more than 3 m.

Reason for decision

The Code’s acceptable solution is prescriptive and the installation does not comply with the requirement.

Where an alternative solution is proposed, the documentation must comply with the requirements of Section 2.3., Division C, in the Code.  The documentation provided in the appeal submission does not comply with the requirements.

Don Pedde
Chair, Building Code Appeal Board

Dated:  October 2, 2025