Vapor Barrier Under Roof Insulation

The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below.

Vapor barrier under roof insulation.

The vapor barrier protects the roof insulation from the vapor included in the interior air. Attic vapor barrier detail for cold climates the best approach for a vented attic in a cold climate is installing a layer of drywall with a good coat of latex paint the paint creates a semi permeable vapor barrier. Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.

This vapor if left unchecked can wet the insulation and over time will reduce the r value of the insulation and lead to mold. 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. It will help you to eliminate problems that may come when the house becomes extremely cold in the winter and terribly hot in the summer. A vapor barrier can be loose laid or fully adhered.

A loose laid vapor barrier is just a big sheet of 6 mil plastic that is. 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. 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. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

In order to add moisture barrier under metal roof you can spray the undersides of the roof by using a thick layer of polyurethane spray foam.