Do I Need A Vapor Barrier For Attic Insulation

If you are planning to have an attic insulation project for your home you may be wondering whether it is important to have a vapor barrier installed as well.

Do i need a vapor barrier for attic insulation.

In mixed climate areas the vapor barrier is optional depending on the total design of a building. Such a location works both as a vapor barrier as well as an air barrier and eliminates the need for an external air barrier not a easy application on a multi storried building as well as any special electrical pans and their sealing. Hence the need to reduce moisture flow into the attic and the need for a vapor barrier. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

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. I install my vapor barrier in the middle of the wall system between the two walls. Whether or not you need a vapor retarder hinges on three main factors. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. 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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. If you need a vapor barrier and your insulation is unfaced you must cover it with a polyethylene film.

This worked well until we added large quantities of attic 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. In cold climates a vapor barrier is almost always needed. 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.