BCAB #1413 - Fire and Sound Separation Between Residential Suites, Article 9.10.3.1. & Sentences 9.10.9.14.(3) & 9.11.2.1.(1)

February 21, 1996

BCAB #1413

Re: Fire and Sound Separation Between Residential Suites, Article 9.10.3.1. & Sentences 9.10.9.14.(3) & 9.11.2.1.(1)

Project Description

The project in question is a wood-frame townhouse building with side by side units, each of which is two storeys high.

Reason for Appeal

Sentence 9.10.9.14.(3) requires dwelling units which contain two or more storeys to be separated by a fire separation with a 1 hour fire resistance rating. Article 9.10.3.1. Permits the design of this separation to conform with Table A-9.10.3.A which forms part of item A-9.10.3.1. in Appendix A of the code. Sentence 9.11.2.1.(1) requires dwelling units to be separated by construction having a sound transmission class rating of at 50.

Appellant's Position

The appellant has chosen wall assembly 26 from Table A-9.10.3.A. which consists two rows of 38 mm x 89 mm studs spaced 25 mm apart, 15.9 mm Type X gypsum board on each side and R-8 glass fibre insulation on one side. The appellant contends that this wall assembly meets both the fire resistance and sound transmission class ratings required for the building in question.

Building Official's Position

The building official has two major concerns about the real world performance of this wall design. First, without physical restraint, such as a layer of gypsum board on the back side of one row of studs, the friction-fit glass fibre insulation will not stay in place throughout the life of the building. This will degrade the sound transmission class rating and possibly the fire resistance rating. Second, there are many instances where framing and services within the wall cavity will interrupt the continuity and/or thickness of the insulation which will also degrade the performance of the wall. The building official also considers the requirement to fill 3/4 of the cavity with insulation applies to the full thickness of the wall system, not the studs on either side.

The Appendix, in item A-9.11.1.1., makes special mention on the attention to detail required for the design and construction of walls required to have a sound transmission class rating. The simplified generic drawing of assembly 26 from Table A-9.10.3.A. does not detail how the extra framing and the installation of services will be accommodated.

Appeal Board Decision #1413

It is the determination of the Board that insulation which fills 3/4 of one stud space meets the requirements of the Code as described in assembly No. 26 in Table A-9.10.3.A. The Board agrees that the insulation must remain in place to perform its intended function.

George R. Humphrey, Chair