Vapor Barrier Roof Insulation

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 barrier roof insulation.

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses. A vapour barrier sometimes referred to as vapour retarder is typically a plastic or foil sheet used for damp proofing to prevent interstitial condensation from forming in various building assemblies such as walls roofs foundations and floors. Avoidance of the installation of vapor barriers such as polyethylene vapor barriers foil faced batt insulation and reflective radiant barrier foil insulation on the interior of air conditioned assemblies a practice that has been linked with moldy buildings lstiburek 2002.

That reduction of air and moisture infiltration can then help improve roof longevity. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. In any case the vapor barrier must point to the warm side. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

Vapor barriers applied over the face of the insulation provide additional benefits in the fight against moisture. What is a vapour barrier.