Attic Insulation Vapor Barrier

Some regions don t require a vapor barrier.

Attic insulation vapor barrier.

Vapor barriers keep the air moisture in your house from condensing in the insulated cavities. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Whether using loose fill or batts put the vapor barrier closest to the warm side of your installation where hot moist air would get in facing the house s interior in cold climates beneath floor insulation and the attic s interior in hot climates on top of floor insulation. If you live in a cold climate place the vapor barrier between the interior of your home and the insulation.

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. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. Not every wall does. When adding additional insulation to an attic that is already insulated never use insulation with a 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. Whether your vapor barrier is a facing or a film it must be placed on the warm in winter side of the wall. 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. 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.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. In any case the vapor barrier must point to the warm side. 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.