The Northwest Wall Moisture Study

The purpose of this study was to find out whether building the exterior walls of new homes to energy-efficient standards with more insulation (at least R-19) and an air/vapor barrier causes unacceptably high levels of moisture or related problems within walls. This was to be determined by field inspection of such homes and openings in their walls. An additional purpose of the study was to determine if any other type of moisture-related problems have occurred in the heavilyinsulated, relatively airtight new homes. Fifty test homes were located in the Seattle-Olympia area, sixteen along the rainy Washington coast, and twenty in the cold Montana region. The exterior walls of the 86 newly constructed homes were opened between January and March 1987 under the worst expected conditions and inspected for signs of moisture, moisture accumulation, or moisture damage. Measurements of the moisture content of selected wood members within the wall cavities also were made. Over half of the test homes had at least one wall wood member with over 20% moisture content. Half of the mud (sill) plates and over one-third of the sheathing were equal to or above 20% moisture content. Whether the walls will dry out sufficiently during warmer weather in order to avoid wood decay and consequent structural damage is unresolved. In addition to the wall cavity moisture problems, numerous moisture-related problems were observed within the homes, primarily because of inadequate moisture control. The results and conclusions of the field study are described in detail. Future research needs also are discussed.