ASHRAE 189.1, "Standard for the Design of High-Performance, Green Buildings Except Low-Rise Residential Buildings," provides guidelines for the use and design of air barriers in roof assemblies. If you are involved with the design of low-slope roof systems, you should know how air barriers function and how they are designed.
Air barriers are used as building envelope components to minimize the amount of air intrusion and air leakage into and out of buildings and building envelope components.
Air barriers and vapor retarders play similar but not identical roles in buildings. Vapor retarders are intended to restrict the passage of water vapor through materials, and air barriers are intended to restrict the passage of air flow through materials.