Do You Need a Vapor Barrier in an Attic?

Identification

• Moisture control is necessary in most climates in the United States. Placing a vapor barrier inside your attic will help reduce moisture. Also known as vapor diffusion retarders, vapor barriers are typically placed in basements and crawl spaces but can provide increased moisture protection in attics, as well. How much moisture that vapor barriers diffuse is measured in units referred to as permeability, or perms.

Types

• Several types of vapor barriers are available for attic installation. Most vapor barriers are coatings or membranes that block moisture. Foam insulation and reinforced plastic materials are often used as vapor barriers in attics. Some types of insulation have vapor barriers built in. Fiberglass roll insulation that has a paper facing is one example of insulation with an added vapor barrier. Paint also acts as a vapor barrier when applied in multiple coats on the attic ceiling.

Effects

• Homes without vapor barriers in the attic often have excess moisture passing through the attic ceiling, which causes the ceiling to remain wet. Constant wetness eventually causes mold growth and structural damage to your home. Adding a vapor barrier to your attic ceiling helps insulate your home and keeps moisture from seeping in through your attic ceiling.

Considerations

• Look underneath your attic insulation to determine if a vapor barrier is in place. Most vapor barriers are plastic, foam or paper and may be attached to insulation. If no vapor barrier is present, it is usually easiest to use paint as a vapor barrier. According to the United States Department of Energy, vapor barrier paints are an effective way to reduce moisture. These paints must be applied in multiple coats to work effectively. After adding a vapor barrier, inspect your attic for large gaps that allow air to escape. Caulk or seal all gaps and check your attic door for airtightness for maximum efficiency.