Published: June 22, 2023
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.
David Finley is the Director of Building Enclosure Science for The Garland Company. His building envelope investigative experience includes water infiltration testing of windows, curtain walls, masonry facades, and plaza and below-grade waterproofing; condensation and air leakage testing of glazed fenestrations and masonry facades; performing hygrothermal analyses using steady and transient state techniques; analyzing window and wall systems for two dimension thermal conduction; and more. David is active in ASHRAE Technical Committees 1.12, 4.4, and 160, and serves as the Program Chair and voting member for TC 1.12, voting member for TC 4.4, and Co-chair of the Freeze-Thaw Task Force for SSPC 160.