Is Roof Membrane Act As An Air And Vapor Barrier

In so much that the roof membrane can often serve as an air barrier it does nothing to prevent this interior air transport.

Is roof membrane act as an air and vapor barrier. It s all about controlling condensation and moisture management within the building envelope. Most roof membranes are class i vapor retarders. Condensation within a roof or wall system can be very damaging to a building s structure attracting mold if it doesn t dry out in a reasonable time and. The lower the perm rating the less diffusion occurs through a material.

It should be noted that all vapor retarders are air barriers but not all air barriers are vapor retarders. There are 3 classes of vapor retarder materials as shown in the figure. That reduction of air and moisture infiltration can then help improve roof longevity. The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system.

A roof design that includes an adhered roof membrane with multiple layers of insulation with board joints offset and staggered over a vapor retarder air barrier helps lower the risk that air and the moisture it carries will infiltrate the roof system. Vapor retarders why are they needed. Vapor retarders do just as they are named they reduce vapor diffusion but not all vapor retarders are equal. When to use a vapor retarder so the question arises.

A vapor retarder can be as simple as a plastic sheet but is not considered an effective air barrier. So while air barriers are part of the building envelope vapor retarders are used within the envelope. When discussing air barriers roofing membranes and the building envelope another important topic comes to mind. When is it prudent to use a vapor retarder.