Vapor Barrier Under Roof Insulation

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

Vapor barrier under roof insulation.

A vapor barrier can be loose laid or fully adhered. 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. This vapor if left unchecked can wet the insulation and over time will reduce the r value of the insulation and lead to mold. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below.

A loose laid vapor barrier is just a big sheet of 6 mil plastic that is. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. 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. Not every wall does.

The vapor barrier protects the roof insulation from the vapor included in the interior air. Polyurethane spray foam metal roof insulation. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. 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.

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.