The Pacific Northwest region of North America is considered to be a mixed-humid climate with moderate temperatures and high moisture levels due to precipitation and relative humidity (RH) throughout the year. Research has been conducted to evaluate the heat and moisture transfer performance of wood-framed wall systems common in residential and multifamily construction using a relative-humidity-dependent vapor retarder. One-dimensional hygrothermal modeling results will be compared to measured data collected in an occupied residential home and a natural exposure testing facility in the Seattle, Washington, area. Wall systems using traditional interior vapor control strategies will be compared with the innovative variable permeability vapor retarder. Building envelope moisture content and RH results were used to support recent national code language changes regarding interior vapor retarder requirements.

Presented at Thermal Performance of Exterior Envelopes of Whole Buildings X – December 2007

Units: Dual