Is Roof Membrane Act As An Air And Vapor Barrier

The purpose of a vapor retarder is to minimize or reduce water vapor diffusion into a low slope roof or wall system.

Is roof membrane act as an air and vapor barrier.

There is often confusion between air barriers and vapors retarders. So while air barriers are part of the building envelope vapor retarders are used within the envelope. A vapor retarder can be as simple as a plastic sheet but is not considered an effective air barrier. 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.

When is it prudent to use a vapor retarder. 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. In so much that the roof membrane can often serve as an air barrier it does nothing to prevent this interior air transport.

Most roof membranes are class i vapor retarders. It should be noted that all vapor retarders are air barriers but not all air barriers are vapor retarders. The lower the perm rating the less diffusion occurs through a material. That reduction of air and moisture infiltration can then help improve roof longevity.

It s all about controlling condensation and moisture management within the building envelope. When discussing air barriers roofing membranes and the building envelope another important topic comes to mind. There are 3 classes of vapor retarder materials as shown in the figure. When to use a vapor retarder so the question arises.