Techniques for Insulating Basements

Ceiling Batts

• In unheated basements, fiberglass batts are installed in the basement ceiling between the floor joists. Each batt is a rolled mat that is held in place and secured using wire strung between the joists. Before you install the batts, check for gaps in the subfloor where pipes and air ducts penetrate. Sealing these gaps using spray foam insulation will prevent cold air from flowing past your insulation into the rest of the house. If there are large pipes or other obstructions between the joists, cut the batts to fit around them rather than compressing the batts to fit into the remaining space.

Wall Batts

• If you have a heated basement, your fiberglass batts will work best if they are installed on the foundation walls. Each batt is put in place and attached to the wall studs using staples. If your basement does not have wooden framing, you can install long pieces of wood -- known as furring strips -- that act as an anchor for the insulation on the wall. If your batts have a vapor retardant backing, make sure it faces toward the interior of the basement.

Foam Board

• Foam board is effective at insulating the interior or exterior of basement walls. Installing foam board on the exterior of an existing home requires excavating around the foundation of your home. Each board is attached to the outside of the foundation using a mastic adhesive and should measure from the bottom of your exterior siding to the average depth of the frost line in your area. Interior foam board is attached to the interior of the foundation walls and reaches from the floor to the underside of the band joist. Foam board inside the basement is installed using special fasteners or furring strips and will require a fire barrier such as gypsum board.

Vapor Barriers

• The warm air from your home contains large amounts of moisture that will condense on the cold surfaces in your basement. Vapor barriers are made from impermeable materials such as roofing paper or plastic sheeting that separate the moisture in the air from your insulation. Vapor barriers are usually attached using staples or tape and should completely cover the insulation.

Rim Joist

• Insulating and caulking the rim joist improves the efficiency of your basement insulation and prevents cold air from leaking into your basement. The rim joist is located between your foundation walls and the subfloor. You can insulate the area in front of the rim joist using batt or rigid foam insulation. Sealing the gaps above and below the rim joist will prevent cold air and moisture from entering your home.