BCAB #1690 - Attachment of Wood Shingles over a Capillary Break, Articles 9.27.2.2. & 9.27.5.1.

January 20, 2011

BCAB #1690

Re: Attachment of Wood Shingles over a Capillary Break, Articles 9.27.2.2. & 9.27.5.1.

Project Description
The project is a single family residence built under Part 9 of the BC Building Code. The proposed exterior wall assembly includes 12.5 mm plywood sheathing, a proprietary sheet product that creates a 10 mm capillary break, and cedar shingles fastened through the capillary break to the plywood sheathing.

Reason for Appeal
A capillary break is required by Sentence 9.27.2.2.(5) between the first and second planes of protection of the cladding system. The attachment of cladding is covered by Article 9.27.5.1. which in Sentence (3) permits wood shingles to be attached to 7.5 mm plywood and in Sentence (5) permits them to be attached to 38 mm x 9.5 mm thick wood lath if the sheathing is not suitable for direct attachment.

Appellant’s Position
The appellant contends that the attachment of the shingles is code compliant as the sheathing used exceeds the minimum sheathing thickness specified in Sentence 9.27.5.1.(3).  The capillary break product also complies with Clause 9.27.2.2.(1)(b) because it provides a 10 mm capillary break that allows drainage and is 80% open.  The cladding is being attached to the sheathing, as permitted, and not to the capillary break product.

Building Official's Position
The building official maintains that although the proprietary sheet material providing the capillary break meets the requirements of  Clause 9.27.2.2.(1)(b) there is no evidence of its suitability as backing for cedar shingles. The building official requires “solid backing” in the form of 38 mm x 9.5 mm wood furring as required by Sentences 9.27.5.1.(5) and 9.27.7.5.(1) or an evaluation report from the Canadian Construction Materials Centre confirming the product is suitable for the attachment of wood shingles.

Appeal Board Decision #1690
It is the determination of the Board that the attachment of cladding, including wood shingles, to sheathing conforming to Article 9.27.5.1. through an intervening material providing a capillary break and conforming to Clause 9.27.2.2.(1)(b) is acceptable.

George Humphrey, Chair