All fifty US States require a continuous air barrier as part of new construction. Code generally contains three compliance options for acceptable air leakage, or permeability, through an air barrier: 0.004 cubic feet per minute per square foot (CFM/ft2) for materials, 0.04 CFM/ft2 for assemblies, and 0.4 CFM/ft2 for the whole building. These standards have trended toward greater levels of air-tightness over time, and will continue to do so, with projected changes to the energy code in the future for the air leakage rate for a whole building getting to a level of just 0.25 CFM/ft2.
In spite of the ubiquity of requirements for air barrier usage, and increasing code standards, there remains a significant amount of confusion and misinformation in the roofing industry regarding air barriers and their distinctions, if any, from vapor barriers and vapor retarders. The goals of this paper are to clarify the definitions and performance characteristics of air barriers, vapor retarders, and vapor barriers; and outline conditions where the performance of an air barrier has a significant impact on the overall building.
