Air barriers, vapor barriers, water-resistive barriers, and insulation

摘要

The purpose of a building enclosure is to control the transmission of air, water (liquid and vapor), and heat. We use different materials in houses to achieve the various levels of control we need, and what any one house needs depends on the climate and on what its occupants do when they're inside. These materials often are described as control layers. A properly enclosed house has a water-vapor control layer, a liquid-water control layer, an air control layer, and a thermal (heat) control layer. Calling them all control layers reminds us that they have a similar task, but they are more commonly known by other names: The water-vapor control layer is also called a vapor retarder or vapor barrier, the liquid-water control layer is also called the drainage plane or the water-resistive barrier (WRB), the air control layer is also called an air barrier, and the thermal control layer is also called insulation. I encounter lots of confusion around the differences among these control layers. While the details of how each one works in relation to the others in any particular house can get complex, the basic distinctions are simple.