BCAB 1971 - Firestopping of noncombustible outlet boxes in a horizontal fire separation below an attic

Firestopping of noncombustible outlet boxes in a horizontal fire Separation below an Attic

Project Description

The project is the construction of several new six-storey, wood frame, residential buildings.

Each building includes an attic space above the sixth storey.  The suite demising walls and public corridor walls do not extend up through the attic space.  Therefore, to maintain the suite-to-suite fire separations the ceiling of the sixth storey is constructed as a fire separation with a one hour fire-resistance rating.  The ceiling assembly consists of two layers of 15.9 mm Type X gypsum board on the underside of framing and the assembly is assigned a fire-resistance rating on the basis of the membrane only, in accordance with Appendix D, D-2.3.12. and Table D-2.3.12., Division B.

It is proposed to install noncombustible electrical outlet boxes that penetrate the ceiling gypsum board membrane layers which form part of the ceiling assembly below the attic.

Applicable Code requirements (BCBC 2018)

Sentence 3.1.8.3.(1), Division B, Continuity of Fire Separations

(1) Except as permitted by Sentence 3.6.4.2.(2), a horizontal service space or other concealed space located above a required vertical fire separation, including the walls of a vertical shaft, shall be divided at the fire separation by an equivalent fire separation within the service space.

Sentence 3.1.9.1.(3), Division B, Fire Stops

(3) Penetrations of a fire separation in conformance with Sentence 3.6.4.2.(2) shall be sealed by a fire stop that, when subjected to the fire test method in CAN/ULC-S115, “Fire Tests of Firestop Systems,” has an FT rating not less than the fire-resistance rating for the fire separation of the assembly.

Article 3.1.9.4., Division B, Penetration by Outlet Boxes

(See Note A-3.1.9.4.)

(1) Except as provided in Sentence (2), outlet boxes are permitted to penetrate the membrane of an assembly required to have a fire-resistance rating, provided they are sealed at the penetration by a fire stop that has an FT rating not less than the fire-resistance rating of the fire separation when subjected to the fire test method in CAN/ULC-S115, “Fire Tests of Firestop Systems.”

(2) Except as provided in Sentences 3.1.9.1.(2) and (3), noncombustible outlet boxes that penetrate a vertical fire separation or a membrane forming part of an assembly required to have a fire-resistance rating need not conform to Sentence (1), provided

(a) they do not exceed

(i) 0.016 m² in area, and

(ii) an aggregate area of 0.065 m² in any 9.3 m² of surface area, and

(b) the annular space between the membrane and the noncombustible electrical outlet boxes does not exceed 3 mm.

Sentence 3.6.4.2.(2), Division B, Fire Separations for Horizontal Service Spaces

(2) If a horizontal service space or other concealed space is located above a required vertical fire separation other than a vertical shaft, this space need not be divided at the fire separation as required by Article 3.1.8.3. provided the construction between this space and the space below is a fire separation with a fire-resistance rating equivalent to that required for the vertical fire separation, except that the fire-resistance rating is permitted to be not less than 30 min if the vertical fire separation is not required to have a fire-resistance rating more than 45 min. (See Note A-3.6.4.2.(2).)

Appendix D, D-2.3.13., Division B, Membrane Penetrations in Combustible and Noncombustible Construction

(1) Where a wall, floor or roof assembly is assigned a fire-resistance rating on the basis of this Subsection and includes a membrane or membranes described in Table D-2.3.4.-A, D-2.3.4.-B, D-2.3.4.-C, D-2.3.4.-D or D-2.3.12., penetrations of the membrane or membranes must be fire stopped in conformance with the applicable requirements in Article 3.1.9.1. or Sentence 9.10.9.6.(1).

Decision being appealed (Local Authority’s position)

The noncombustible outlet boxes penetrating the membrane ceiling below the attic must be sealed at the penetrations with a firestop system.

The exception that permits the use of noncombustible outlet boxes without a firestop specifically applies to vertical fire separations only; the exception does not apply to horizontal fire separations.  The exception also applies to membranes forming part of an assembly required to have a fire-resistance rating that does not act as a fire separation.

Appellant's position

Noncombustible outlet boxes are permitted to penetrate the gypsum board ceiling without firestopping at the ceiling below the attic.  The Sentence (2) phrase, “assembl(ies) required to have a fire-resistance rating”, can apply to assemblies acting as horizontal fire separations.

The installation must comply with the requirements outlined in Clauses (a) and (b) of Sentence 3.1.9.4.(2).

Appeal Board Decision #1971

The Board varies the decision of the local authority.

It is the determination of the Board that, subject to some limitations, noncombustible outlet boxes can penetrate a membrane forming part of an assembly required to have a fire-resistance rating, including a membrane forming part of a horizontal fire separation, without being sealed at the penetration by a fire stop.

However, this attic (i.e., horizontal service space) is equipped with a horizontal fire separation below the attic in lieu of continuing the vertical fire separations that are located below the attic up through the attic.  In this case, any penetration of the horizontal fire separation must be sealed at the penetration by a fire stop having an FT rating not less than one hour.

Reason for decision

The Board considers that the phrase “membrane forming part of an assembly required to have a fire resistance rating”, as found in Sentence 3.1.9.4.(2), Division B, can apply to membranes forming part of assemblies acting as horizontal fire separations.  The area, aggregate area, and annular space limitations outlined in Sentence (2) apply.

However, where a vertical fire separation terminates at the underside of the ceiling as permitted by Sentence 3.6.4.2.(2), Division B, and a horizontal fire separation is used instead – a circumstance commonly referred to as “a 3.6.4.2. ceiling” – all penetrations of the horizontal fire separation, including those for noncombustible outlet boxes, must be sealed with a fire stop having an FT Rating not less than fire-resistance rating of the horizontal fire separation.

The fire stop requirement, as it applies to a “3.6.4.2. ceiling”, is outlined in Sentence 3.1.9.1.(3), Division B, is referenced in Appendix D, Sentence D-2.3.13.(1), Division B, and is also referenced at the beginning of Sentence 3.1.9.4.(2), Division B, as an exception to the no-fire-stop permission stated in that Sentence.

Don Pedde
Chair, Building Code Appeal Board

Dated:  June 19, 2025