BCAB #1614 - Window Installation, Sentence 9.25.3.3.(6), Sentences 9.25.4.1.(1) and 9.25.4.3.(1)

November 23, 2005

BCAB #1614

Re: Window Installation, Sentence 9.25.3.3.(6), Sentences 9.25.4.1.(1) and 9.25.4.3.(1)

Project Description

The subject is the installation of factory built windows in a wood frame residential building.

Reason for Appeal

The BC Building Code does not specifically describe methods for window installation. Sentence 9.25.3.3.(6) requires penetrations of the air barrier system, such as those created by the installation of windows, shall be sealed to maintain the integrity of the air barrier system over the entire surface. Sentence 9.25.4.1.(1) requires thermally insulated wall assemblies be constructed with a vapour barrier to provide a barrier to diffusion of water vapour from the interior into wall spaces. Sentence 9.25.4.3.(1) requires vapour barriers be installed to protect the entire surfaces of thermally insulated wall assemblies.

Appellant’s Position

The appellant has used the following method for window installation to comply with the Building Code’s air barrier vapour barrier requirements.

  • The integrity of the air barrier is met by the window flange being caulked to the wall and on the interior the polyethylene caulked to the window frame and caulking the finished wood liner and trim to the window and drywall.
  • The requirement for a continuous vapour barrier is met by the polyethylene being caulked to the window frame.

The appellant considers the additional window installation details requested by the Building Official are not mandatory Code requirements.

Building Official's Position

The Building Official is requesting the window installation include spacer shims below the window unit to allow for drainage, a waterproofing membrane protecting the rough opening sill, and provisions for a sill dam on the interior side. This protection is considered necessary should airborne vapor condense on a non-thermally broken window flange and then accumulate on unprotected wood framing.

Appeal Board Decision #1614

It is the determination of the Board that the additional window installation details requested by the Building Official are not mandatory prescribed requirements of the Code.

The air barrier and vapour barrier design, as proposed, complies with the Code.

George Humphrey, Chair