BCAB 1965 - Requirements for the installation of flashing

Requirements for the installation of flashing

Project Description

The project is the design and construction of a new house with wood shingle exterior cladding.

The exterior wood-frame walls will be covered with a proprietary, lapped, vapour-permeable, combined air barrier and sheathing membrane that also wraps into the window rough openings.  Windows will then be installed such that the window flanges will be outboard of the membrane.  The windows will be, in various manners, sealed to the membrane to provide continuity of the air barrier system.

It is proposed that the tops of the windows will have a metal flashing installed outboard of the top window flange.  The upper portion of the flashing will then be covered with a proprietary membrane tape that will extend upward and be adhered to the sheathing membrane.  The intention is to avoid any discontinuity of the air barrier membrane that could be introduced by cutting or interrupting the membrane to tuck the flashing inboard of the membrane.

Applicable Code requirements (BCBC 2024)

Sentence 5.6.1.2.(1), Division B, Installation of Protective Materials

(1) Where protective materials are applied to assemblies to provide the required protection from precipitation, they shall be installed so as to shed precipitation or otherwise minimize its entry into the assembly and prevent its penetration through the assembly. (See Note A-5.6.1.2.(1).)

Note A-5.6.2.1. Sealing and Drainage. (excerpt)

A number of different design solutions can provide an environmental separator with the minimum performance level necessary to effectively control environmental and structural loads and their effects.  An appropriate solution is selected on the basis of the applied load characteristics, the performance achieved by the solution, and its durability over the design service life.  It is incumbent on the designer to balance the performance of a particular design solution against the required performance level, the risk of failure, and the consequences of failure for the building and its users . . .

Sentence 9.27.1.1.(1), Division B, General

(1) Where lumber, wood shingles, shakes, fibre-cement shingles, planks and sheets, plywood, OSB, waferboard, hardboard, vinyl, insulated vinyl, polypropylene, aluminum or steel, including trim and soffits, are installed as cladding on wood-frame walls or above-ground flat insulating concrete form walls exposed to precipitation, the cladding assembly shall comply with

(a) Subsections 9.27.2. to 9.27.13., or

(b) Part 5.

Sentence 9.27.3.8.(4), Division B, Flashing Installation

4) Flashing described in Sentences (1) and (3) shall

(a) extend not less than 50 mm upward inboard of the sheathing membrane or sheathing installed in lieu of the sheathing membrane (see Article 9.27.3.4.),

Decision being appealed (Local Authority’s position)

The Code requires that a sheathing membrane cover a flashing by 50 mm and there is no allowance for flashing tapes.

Appellant's position

The air barrier flashing detail using a membrane tape is widely used and industry-supported, is endorsed by building envelope professionals, and is published and utilized by BC Housing.  A traditional positive lap flashing installation conflicts with air barrier continuity.  Recognition and acceptance of a best practice as Code-compliant, without the cost of engaging a professional engineer on a case-by-case basis, is requested.

Appeal Board Decision #1965

The Board confirms the decision of the local authority.

It is the determination of the Board that the applicable requirement in Part 9 requires the sheathing membrane to lap over the flashing by not less than 50 mm.

Reason for decision

The requirements related to the installation of cladding in the Part 9 Articles are prescriptive.  As alternatives for Code-compliance, cladding installations may conform with the performance-based requirements in Part 5 or may be the subject of an alternative solution.

In this case, no representation has been made regarding compliance with Part 5 and no alternative solution has been proposed.

Don Pedde
Chair, Building Code Appeal Board

Dated:  May 29, 2025