Insulating Crawl Spaces with STYROFOAMâ„¢ insulation

1. Remove anything that will get in the way of installation. Stand STYROFOAM extruded polystyrene insulation panels on the footings and run them up the inside of the crawl space wall to within 2" of the top of the wall. This 2" uninsulated strip simplifies future termite inspections. It may be most convenient to work with the long edge of the board to the ground.

Figure 1

2. Attach panels to the foundation using one of these methods:

• Concrete nails and 1"-diameter washers
• Spots of compatible adhesive
• Adhesive-attached spindle anchors and speed clips

3. Insulate the inside of the band joist with either fiberglass batts with vapor barrier facing to the inside of the crawl space or with pieces of foam cut to fit tightly.

Figure 2

4. To reduce ground moisture from entering the crawl space, lay a 6-mil polyethylene film on the ground and turn it up against the foam on the wall. Seal the film to the foam using tape or a compatible adhesive.

Figure 3

5. This foam/vapor retarder combination reduces relative humidity in the crawl space. Generally, the building codes will require 1 square foot (sf) of vent area for each 1,500 sf of floor area when a retarder (such as polyethylene film) is placed on the crawl floor. Note: Some vents may need to be left open to provide combustion air for a furnace located in a crawl space. Check with your heating contractor or building inspector.

Limitations

Insulating the walls in your crawl space is a great way to save energy, but there are limitations to consider. If either of the following conditions applies to your crawl space, it is better to nail STYROFOAM extruded polystyrene insulation to the underside of the floor joists or to install batt insulation between the floor joists over the crawl space. If STYROFOAM is nailed to the underside of the floor joists, it must be covered by a code defined ignition barrier such as 1/4" plywood, 3/8" particleboard or 3/8" gypsum wallboard.

• You are in an area of high radon concentration
• You often have running or standing water in your crawl space

About building codes

The following reports from model building code organizations allow STYROFOAM extruded polystyrene insulation uncovered on the inside of crawl space walls when certain conditions are met. Please refer to them, or contact your local building inspector:

• NES NER-699