Field Monitoring of Wall Vapor Control Strategies in the Pacific Northwest

Panel: Residential Buildings: Technologies, Design, Performance Analysis, and Building Industry Trends

Authors:
Kohta Ueno, Building Science Corporation
Aaron Townsend, Building Science Corporation
Michael Lubliner, Washington State University

Abstract

A twenty-seven month field test comparing the performance of a variety of vapor control layers was conducted in a full-scale test facility in the marine climate of Olympia, WA. The vapor control layers included latex paint on drywall, polyethylene film, Kraft paper, and a variable-permeance polyamide film. One goal of this testing was to compare performance with the most recent building code recommendations. A data acquisition system recorded hourly indoor, outdoor and stud bay temperature and RH measurements as well as wall framing and sheathing moisture contents. The long-term data show seasonal wetting and drying of the assemblies. The latex-paint-only wall exterior sheathing moisture contents were found to be the highest, reaching or exceeding 22% during all three monitored heating seasons. The polyethylene, variable-permeance polyamide film, and Kraft walls had lower moisture contents, with the polyethylene wall being the slowest to wet and also to dry. Visual observations during disassembly at the end of the monitoring revealed minor mold patterns on the exterior sheathing in some of the test sections. The wetting pattern of the sheathing provides evidence that inset stapling results in convective air flow that bypasses the vapor retarder, resulting in condensation and accumulation at the top of the exterior wall sheathing. Recommendations are made to conduct further research on the issue of convective moisture bypass.