Evaluation of Moisture Problems in Exterior Wall Assemblies

Abstract

Many buildings, especially those in hot and humid climates, have problems with moisture infiltration into the exterior wall assembly. This can lead to premature deterioration of the finish materials and/or lead to poor interior air quality. In addition to water leakage, these moisture problems can take the form of mold and mildew growth, and can contribute to high humidities inside of buildings. Absorptive cladding materials such as masonry can present additional challenges because of the high moisture content that can be created due to water stored within the exterior wall assembly. The source of the moisture infiltration is difficult to identify at times, since there is often no obvious signs of water entry during rainstorms. Both water infiltration and air infiltration can deposit moisture within walls. Moisture stored within the walls will redistribute as a result of evaporation and will condense behind vapor-impermeable wall coverings and other surfaces that are below the dew point temperature of the air. The moisture problems are sometimes attributed to air infiltration while potential water leakage problems are ignored. At other times, the problems are attributed to water leakage where, in fact, air infiltration may play a factor. What is required is an understanding of all potential contributors to moisture problems so that an appropriate and complete investigation can be conducted. Only after all the conditions that are contributing to the moisture intrusion problems are identified can effective repairs be made.