BCAB #1780 - Attachment of Wood Shingles over a Capillary Break

March 17, 2016

BCAB #1780

Re: Attachment of Wood Shingles over a Capillary Break, Clause 9.27.2.2.(1)(b) & Sentence 9.27.5.1.(1)

Project Description

The project is an addition to a single family house required to conform to Part 9 of the 2012 BC Building Code.  The cladding proposed is cedar shingles and is attached to code compliant sheathing.

Reason for Appeal

The appellant is proposing to use a proprietary roll type product to create the required capillary break behind the cladding.  Because of the use of this product, the building official has determined that the attachment of cladding does not comply with Sentence 9.27.5.1.(1). 

Appellant's Position

The appellant considers that the proprietary product meets the requirements of Clause 9.27.2.2.(1)(b) for “an open drainage material, not less than 9.5 mm thick and with a cross-sectional area that is not less than 80% open”.   The use of this product is permitted as a prescriptive solution under Part 9 of the Code and does not require the use of Part 5 or the code’s Letters of Assurance.  The cladding is proposed to be attached to sheathing of a minimum thickness that complies with Sentence 9.27.5.1.(3), and fastened in accordance with Article 9.27.7.3 and Table 9.27.5.4.

Local Authority’s Position

The building official maintains that, although the product in question is a minimum of 9.5mm thick and is 80% open as required by 9.27.2.2.(1)(b), its other properties as part of a cladding system have not been evaluated.  The code’s assumptions of compression, contact and friction are no longer present when a medium is introduced between the cladding and the supporting element in order to create a capillary break.  The fasteners in the code have been specified based on the shank being fully supported.  With the introduction of an intervening material in the capillary break, it is no longer known if the fastener lengths specified are appropriate.  Due to the foregoing, the attachment of cladding does not comply with Sentence 9.27.5.1.(1).  It is further unknown how this assembly will perform its intended function over time.

Appeal Board Decision #1780

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 acceptable intervening material providing a capillary break and conforming to Clause 9.27.2.2.(1)(b) and Sentence 1.2.2.1.(1) is compliant.  

This decision is limited to the attachment of cladding through the intervening material and does not include the approval of the intervening material itself.   In addition to the requirements of 9.27.2.2.(1)(b), the intervening material must also comply with Sentence 1.2.2.1.(1) of Division A and Article 2.2.2.1. of Division C.

Professional design and review (Letters of Assurance) have not been considered in this appeal.

Reasons for Decision

This decision is consistent with Appeal #1690.

The code does not specify direct attachment of cladding is required (without an intervening material).

Requirements for Letters of Assurance are not identified on the application form or in correspondence with the building official.

Lyle Kuhnert, Chair, Building Code Appeal Board