BCAB #1854

March 18, 2021

Re: Deck surface material

Project description

The subject project is the reconstruction and increase in area of a deck at the rear of a two-storey house. The deck will be approximately 5.8 m by 4.2 m and primarily uncovered, except for a portion covered by the house’s 0.6 m eave overhang. The deck has a 2% slope towards the deck’s edge away from the house to provide drainage. The guard provided does not impede the drainage.

The deck’s walking surface is plywood covered with a waterproof membrane. The waterproof membrane does not comply with the roofing standards specified in Table 9.26.2.1.B, nor is any evidence provided that the system complies with Part 5.

The underside of the deck is open without ceiling/soffit finish material and does not protect any space or intended occupancy below.

Applicable Code requirements

Sentences 9.26.1.1.(1) and (2) and 9.26.1.2.(1) and (2) of Division B of the British Columbia Building Code 2018.

9.26.1.1.(1) For the purpose of this Section, the term “roof” shall mean sloped or near-horizontal assemblies that protect the spaces beneath them, including platforms that effectively serve as roofs with respect to the accumulation or drainage of precipitation. (See Note A-9.26.1.1.(1).)

A-9.26.1.1.(1) Platforms that Effectively Serve as Roofs. Decks, balconies, exterior walkways and similar exterior surfaces effectively serve as roofs where these platforms do not permit the free drainage of water through the deck. When water is driven by wind across the deck (roof) surface, it can be driven upward when it encounters an interruption.

(2) For the purpose of this Section, the term “roofing” shall mean the primary covering for roofs.

9.26.1.2.(1) Roofs shall be protected with roofing, including flashing, installed so as to

a) effectively shed water,

b) prevent the ingress of water and moisture into building assemblies and occupied space, and

c) minimize the ingress of water due to ice damming into building assemblies.

(2) Compliance with Sentence (1) shall be demonstrated by conforming to

a) the remainder of this Subsection, or

b) Part 5.

Decision being appealed (local authority’s position)

The local authority has determined that the deck surface must be designed and constructed in accordance with Subsection 9.26.1. for roofing. The membrane must be considered a roofing membrane.

Appellant's position

The appellant maintains that within its definition in Sentence 9.26.1.1.(1), a roof is an assembly that protects the spaces beneath them. The appellant contends in the subject circumstance, the deck is not protecting the space below, as it is not intended to shelter an occupancy. The previous deck surface was spaced boards which allowed water to drain through to the area below.

The appellant’s understanding of the position of the local authority is that the surface could accumulate precipitation and is not constructed to drain freely.

Appeal Board decision #1854

It is the determination of the Board the subject deck as constructed, which does not provide free drainage through the surface, is to be considered a roof, and the deck membrane must comply with those requirements for roofing.

Reason for decision

The Board has consulted with the National Research Council Canada with respect to the wording and intent of Sentence 9.26.1.1.(1). The response was emphatic in stating: “A platform such as a deck, balcony, or exterior walkway is required to be protected as per the requirements in 9.26.1.2. if the platform does not permit free drainage of water through the deck, regardless of whether or not it protects a space beneath it.”   

Further, Proposed Change Form 688 indicated the existing wording is confusing in that it might be interpreted that exterior surfaces of decks and balconies need not be treated as roofs where water drains at the edge.

The Board notes that the use of Part 5 in Sentence 9.26.1.2.(2) is specifically included as an alternative for compliance which may lead to different options.

Lyle Kuhnert

Chair, Building Code Appeal Board