Attic Vapor Barrier

Attic vapor barrier detail for cold climates.

Attic vapor barrier.

A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective. Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. Most forms of attic insulation benefit from the addition of a vapor barrier to protect them from the harmful effects of moisture which can reduce their effectiveness over time the following are a few simple steps to help you undertake the task properly so your vapor barrier retains heat without damaging the insulation. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.

Some regions don t require a vapor barrier. In existing spaces oil based paints or vapor barrier latex paints offer an effective moisture barrier. 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. Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic.

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.