Does Attic Insulation Need Vapor Barrier

The facing on faced insulation acts as a vapor retarder.

Does attic insulation need vapor barrier.

With the added insulation the attic stayed cold and so did the ventilating air from outside which was now unable to effectively remove attic moisture. To be able to answer this question correctly for your home there are a few factors you need to consider before any major attic insulation project. In cold climates a vapor barrier is almost always needed. Hence the need to reduce moisture flow into the attic and the need for a 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. 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. Whether or not you need a vapor retarder hinges on three main factors. In mixed climate areas the vapor barrier is optional depending on the total design of a building.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. This worked well until we added large quantities of attic insulation. 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 insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below.