Can You Put Insulation in a Crawlspace?

Vented Crawlspace

• A crawlspace with at least two exterior openings is designed to control moisture via ventilation. Still, moisture can build up during humid weather. If you insulate a vented crawlspace, you will need to install a vapor barrier. These barriers are designed to keep moisture from entering the living areas of your home and damaging your insulation. The vapor barrier in this kind of crawlspace should go under the insulation to separate it from the crawlspace and across the dirt or gravel floor of the crawlspace.

Floor Insulation

• The main method of insulating a vented crawlspace is to install insulation under the subfloor, between the floor joists. Batt insulation made of fiberglass is often used for this purpose, because it is easier to secure between the joists than loose-fill insulation. When installing insulation between your floor joists, make sure that the area is dry and that the insulation is seated firmly between the joists. To ensure that your insulation stays in place, use a lightweight mesh of metal wire or nylon cord to secure it. Fasten the mesh or cord to the floor joists every 12 inches.

Sealed Crawlspace

• If your crawlspace is not ventilated, the most effective method is insulating the foundation walls. Insulating an unvented crawlspace typically requires less insulation and is more effective at preventing freezing damage to pipes. This method is only effective, though, if your crawlspace is sealed against moisture and outside air. Installing a vapor barrier across the floor of the crawlspace and sealing openings in foundation walls and subfloor will help to minimize the moisture in your crawlspace.

Wall Insulation

• In a crawlspace that is not vented, you have the option of using foam board or batt insulation around the walls of the foundation instead of below the subfloor. This type of insulation is more susceptible to damage from rodents and insects and requires regular inspection to remain effective. You must ensure that the access hatch for the crawlspace is sealed and ensure that any water heaters or other combustion-powered appliances will not vent fumes into your crawlspace.