Moisture Measurements and Condensation Potential in Wood Frame Walls in a Hot-Humid Climate

It has long been noted that interior vapor barriers in wood frame walls in hot-humid climates can lead to interstitial condensation within walls. The bases for this recognition are predictive simulations, anecdotal observations, and a limited number of experimental studies. This paper describes an experimental study conducted in a hot-humid climate that investigated the influence of an interior vapor retarder and compares observed performance with simulation predictions. The wall performance data reviewed here was gathered as part of a larger test program evaluating the performance of a range of typical wood frame, residential wall constructions in a hot-humid climate. The approach chosen was to use real-time field exposure using a "test hut" located in Tampa, Florida. The test hut had two long sides, which provided the ability to test 16 wall specimens each. Wall specimens were instrumented with a variety of temperature, humidity, and moisture sensors. In addition to natural weather exposure, the wall specimens could be manually wetted by a water injection system to simulate rain leakage. More specifically, this paper focuses on using the data collected before and after the installation of an interior vapor barrier (vinyl wallpaper) to show the change in moisture loading and the potential condensation within the walls resulting from the installation. The field data is compared with predictions of the wall behavior using a commonly available hygrothermal model. There is increasing reliance on the use of predictive models to assess the moisture performance of building assembly designs. These predictive models need to be validated against real data to test their variance from real systems.