General

With improved insulation requirements in modern energy codes, “green” codes, and above-code energy efficiency programs, envelope assemblies allow less thermal energy transfer resulting in energy savings. This benefit comes with a climate-dependent consequence: colder surface temperatures on materials to the interior side of an air-conditioned building in the summer, or exterior side in the winter. When these cooled surfaces are exposed to moisture-laden air leaks (from the exterior in the summer or from the interior in the winter) or excessive vapor diffusion through the assembly, they become more prone to condensation and moisture accumulation. Fortunately, this problem has durable solutions as discussed in this section.

An effective air barrier installation (Section 4.3.2) and vapor diffusion control strategy (Section 4.3.3) have become increasingly important to the durability of modern energy efficient homes. Furthermore, new homes usually have a significant quantity of “built-in” or initial moisture embodied in materials like concrete and lumber which will create additional water vapor loads during the first year or so of a building’s operation as those products dry. Thus, reduction of “built-in” construction moisture has also increased in importance (Section 4.3.4).