Installing Attic Insulation: Vapor Barriers & Ventilation

Vapor barriers and ventilation are an important part of an insulation job. They help to ensure the appropriate movement of both air and moisture throughout your home.

What are vapor barriers?
Water from the warm air inside your home will seek out the cooler areas of your home in cold weather. Some of the places where it commonly collects include the underside of your roof, exterior walls, and your insulation.

Left unchecked this condensation can damage your home in a variety of ways, including causing paint to blister, damaging the roof, rotting wood framing, and destroying insulation. These problems can be minimized by the use of a vapor barrier installed between insulation and interior surfaces.

Vapor barriers, usually in the form of coated kraft paper or foil-backed paper, are sometimes attached to batt or blanket insulation. When using insulation that does not include a vapor barrier you can four- or six-millimeter thick polyethylene sheeting. This also works well if you are using a loose-fill or foam insulation.

Following are some important tips for installing a vapor barrier with your insulation:

• The vapor barrier should be placed toward the warm side of any installation, downward on the attic floor or on the interior side of walls for example
• Do not add a second vapor barrier when installing a second layer of insulation, as this can trap moisture in your first layer of insulation. If you have existing insulation be sure to use batts or blankets that do not have a vapor barrier attached, or if that is not available be sure to cut holes it the vapor barrier every few inches to achieve proper air flow
• Tightly tape any sections of vapor barrier that tear during installation
• You can reduce condensation in your crawlspace by adding a polyethylene vapor barrier to the floor of the area

Important points about ventilation
You need to have vents in your attic to ensure proper circulation of fresh air throughout your attic. During the warm summer months heat can be trapped in an unventilated attic that will increase the temperature of your home and make your cooling appliances work harder. During the winter months ice dams that can damage your roof can be caused by warm air trapped in your attic.

There are several choices when it comes to placing attic vents. Newer homes, especially in the Midwest, often include both soffit and continuous ridge vents.

Attic vents should never be covered by your insulation. You should add several vents if you are adding insulation to an attic that does not have vents. You can get information on the proper products to use from your local contractor or home center.

A heat recovery ventilator will give you the best energy savings and improved indoor air quality. The keep the air in your home healthy a heat recovery ventilated provides for the continuous circulation of air throughout your home.

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