Attic Insulation Vapor Barrier Or Not

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Attic insulation vapor barrier or not.

The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor. Every construction material has an element of permeability to water which is why you need to have a vapor barrier to damp proof your home and attic. 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. 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.

On the other hand an air barrier a properly detailed air tight drywall ceiling for example in the absence of a vapor barrier can be effective since it stops the flow of vapor laden air. A damp attic can also be the cause of discomfort and lower air quality in the living space. 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. 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.

When adding additional insulation to an attic that is already insulated never use insulation with a vapor barrier. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Not every wall does.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. 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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below.

In any case the vapor barrier must point to the warm side. Some regions don t require a vapor barrier.