The Need for Dedicated Air Barriers within Low-Slope Roofing Assemblies

Abstract

There are different opinions within the roofing industry regarding the need for dedicated air barrier layers within roofing assemblies. A dedicated air barrier is a separate layer within the roofing assembly that is provided to meet the needed performance for air infiltration and air exfiltration and to limit air movement from the building interior into and out of the roofing assembly. Many members of the design, materials manufacturing, and construction arms of the roofing industry cannot seem to come to a clear agreement that providing a dedicated air barrier layer within roofing assemblies is necessary, as well as good practice. Are dedicated air barriers required in roofing assemblies? What benefit do they provide? What risks do they impose? What risks are there if they are not provided? This paper addresses these questions and explores and identifies applicable code requirements, long- and short-term performance impacts, and it also details concerns and opportunities and discusses the impact of dedicated air barriers on the sustainability of buildings and roofs. It addresses the potential risks and benefits of dedicated air barrier layers and recommends when and where these barriers should be provided. One area of confusion in this issue is the difference between air leakage of the roof and air intrusion into the roofing assembly. Air transferring back and forth between a roofing assembly and a building interior presents risks that must be evaluated when considering the need for dedicated air barriers. Properly addressing both air leakage and air intrusion is fundamental to the performance goals of a building, as well as to the design and construction of a roof system to meet those goals. This paper also addresses the future research and standards that are needed to understand the impacts of providing, or not providing, dedicated air barrier layers within roofing assemblies.