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Published: June 22, 2023

Updated: June 19, 2025

Understanding Air & Vapor Barriers

In the realm of commercial roofing, the importance of continuous air and vapor barriers is paramount for ensuring energy efficiency, moisture control, and occupant comfort. Our technical white paper, "Breaking Through Barriers: How Understanding Air and Vapor Barriers Can Help Ensure More Comfortable, Safer Buildings," provides a comprehensive analysis of these critical components.

Air Barriers

StressPly Legacy - Amesbury Middle School - Rob Verreault

Continuous Air Barriers: Enhancing Building Efficiency

All fifty U.S. 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.

 

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.

 

Learn more about the definitions and performance characteristics of air barriers, vapor retarders, and vapor barriers. The white paper also outlines conditions where the performance of an air barrier has a significant impact on the overall building. 

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Commercial Roofing Code Requirements

Navigating commercial roofing code requirements is essential for compliance and ensuring the longevity of roofing systems. The codes dictate specific standards for air leakage and vapor barrier performance, impacting the choice of materials and installation techniques. Understanding these requirements helps in selecting appropriate high-performance roofing systems that meet regulatory standards and enhance building efficiency.

 

Compliance options for air leakage through an air barrier are 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.

Historic Anderson County Courthouse in Palestine, Texas with Drone. Restored with Silver-Shield, Optimax in Weatherking Flexbase, and Stressbase 80 as a vapor barrier. Insulation down in Insul-Lock. Features LiquiTec and R-Mer Wall Panels

The Role of Vapor Barriers in High-Performance Roofing Systems

Vapor barriers play a crucial role in high-performance roofing systems by limiting the diffusion of water vapor through building enclosures. These barriers prevent moisture-related issues, such as condensation and mold growth, ensuring the structural integrity and longevity of the roof. Selecting the right vapor barrier involves understanding its permeability and the specific needs of the building.



david-finley

About the Author

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. 

Read the White paper

In this informative technical white paper, you will: understand the differences between an air barrier, a vapor barrier, and a vapor retarder; learn the risks inherent in a mindset that "the building needs to breathe;" and see how building code regarding air barriers has changed over time. Click Download PDF to access the full document.