Vapor Membrane Roof

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

Vapor membrane roof.

There is often confusion between air barriers and vapors retarders. And the membrane on the bottom is also a vapor barrier. That reduction of air and moisture infiltration can then help improve roof longevity. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful.

The roof is a large part of the building envelope and therefore has a significant impact on the flow of energy in and out of buildings. The bottom membrane s primary function is that of an air barrier but it s material characteristics are such that historically it has also been a vapor barrier. Vapor control membranes play a very important role in this. The firestone v gard vapor control membrane is designed to be used as vapor control layer in firestone roofing systems.

Everyone knows that water in roof systems is never a positive. The billowing roof membrane can also create a sound issue for the owner as it flaps up and down. 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.

A vapor retarder is a material or system that is designed as part of the roof system to substantially reduce the movement of water vapor into the roof system where it can condense. Because of the billowing effect a mechanically attached roof membrane does not count as an air barrier.