Is Roof Membrane Act As An Air And Vapor Barrier

When discussing air barriers roofing membranes and the building envelope another important topic comes to mind.

Is roof membrane act as an air and vapor barrier.

It should be noted that all vapor retarders are air barriers but not all air barriers are vapor retarders. When is it prudent to use a vapor retarder. Newer self adhered membrane products act both as air and vapor barriers and can act as temporary roofs to dry in the building until the remainder of the roof assembly is installed. It s all about controlling condensation and moisture management within the building envelope.

That reduction of air and moisture infiltration can then help improve roof longevity. Vapor retarders do just as they are named they reduce vapor diffusion but not all vapor retarders are equal. Vapor retarders and air barriers. 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.

A vapor retarder can be as simple as a plastic sheet but is not considered an effective air barrier. Most roof membranes are class i vapor retarders. There is often confusion between air barriers and vapors retarders. There are 3 classes of vapor retarder materials as shown in the figure.

Vapor retarders why are they needed. In so much that the roof membrane can often serve as an air barrier it does nothing to prevent this interior air transport. The lower the perm rating the less diffusion occurs through a material. So while air barriers are part of the building envelope vapor retarders are used within the envelope.