Vapour Barrier Attic Insulation

A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

Vapour barrier attic insulation. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. During the energy crisis of the 1970s a prevailing belief took root where it was thought that tightly sealing walls and ceilings with a vapor barrier was essential to blocking heat transference and reducing energy costs it was soon determined however that unless the seal was absolute moisture that did get into sealed walls could create serious structural problems and health issues such as. In any case the vapor barrier must point to the warm side. If you do there is a chance that moisture that has slipped by the first vapor barrier will become trapped by the second vapor barrier decreasing the value of your insulation.

The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. When adding additional insulation to an attic that is already insulated never use insulation with a vapor barrier.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Do not add a vapor barrier on top of the insulation in your attic since the paper facing on the existing insulation is the vapor barrier. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. Not every wall does.

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. Now with attic insulation heat is no longer lost from the living space such that moisture may remain trapped in the attic vapor barriers were therefore necessary to reduce moisture flow into the attic.