The publication of the 2003 International Residential Code mandated water-resistive barriers as part of exterior wall assemblies. Spurred by increasing costs of energy for heating and cooling homes and the desire for a reduced carbon footprint, there has also been a trend to increase insulation in the building enclosure. These combined goals of water resistance, and a tighter building envelope to control energy costs, often result in a lack of heat and air transmission across wall assemblies. This can mean trapped moisture within sidewalls that has little opportunity to dry, especially in rainy or humid climates.
Residential builders, architects and homeowners have now had over a decade of experience working and living with these requirements and are finding that a WRB, while good, may not always be an adequate solution for keeping wall assemblies dry. Buildings experience serious issues when water gets trapped behind siding. It can cause mold, rot and significant structural damage that can be expensive to repair.