How to Insulate an Interior Basement Wall

Basements are built without insulation and tend to be cool and often damp spaces. Insulating will improve a basement's usefulness and add value to a house. It also can help cut heating and cooling bills by making the house more energy-efficient. Repair any cracks or damage in the basement walls and make sure they are waterproofed before you add insulation. Any moisture in the walls will be trapped behind insulation and can lead to mold buildup. Build any partition walls needed to divide the space before you insulate, normally with standard 2-by-4-inch framing.

Step 1

Determine how much insulation you need and decide what type to use; combine types if necessary for best results. Follow recommendations of the International Energy Conservation Code for R value or heat resistance required. The website has useful references on insulation types required for each state.

Step 2

Compare material costs and installation methods before choosing a type. Use extruded polystyrene rigid foam board on perimeter walls in most basements because it is more moisture-resistant than fiberglass batts. Install either foam board or fiberglass batts on ceilings or other walls. Base your choice on the R value required and cost.

Step 3

Insulate the band joists or space where the house walls rest on the foundation. Press fiberglass batts into the cavity, or cut rigid extruded polystyrene board to fit. Use unfaced fiberglass batts, without a moisture barrier on one side, to avoid trapping any moisture under the house flooring. Cut either foam board or fiberglass to fit with a utility knife.

Step 4

Put fiberglass batts or XPS foam board between joists in the basement ceiling. With a construction stapler, fasten fiberglass batts to wooden joists with staples through the paper lips, unless there is a moisture barrier above the ceiling. Press unfaced batts or cut foam board panels to fit tightly between joists if there is a moisture barrier.

Step 5

Install XPS foam board on the inside of perimeter walls. Use 2-inch foam for an R-10 value adequate for most of the country, thicker panels if more R value is needed. Put up foam board either before or after installing any studs or furring strips; put studs or furring strips over foam panels or set panels between cavities if studs are placed first. Cut panels to fit with a utility knife.

Step 6

Fasten fiberglass panels with an adhesive recommended by the foam manufacturer, or with concrete nails with plastic washers under the heads. Test the adhesive in a small area to make sure it will bond the foam tightly to the wall. Glue foam board directly to concrete walls if they are properly waterproofed. Spread adhesive in strips on the walls from a tube, press the panels firmly into place and hold them briefly until they are secure.

Step 7

Seal seams between foam panels and around windows or other openings with tape from the manufacturer. Tape over studs or furring strips if panels are set between them.

Step 8

Fill cavities between studs on interior partition walls with either rigid foam or fiberglass batts. Put rigid foam panels between the studs, secured with drywall on either side of an interior partition wall, or staple fiberglass batts to the studs through the installation flaps on the side of the batts. Adapt this insulation to the thickness of the wall.

Step 9

Cover all insulation with drywall for fireproofing. Use gypsum wallboard at least 1/2-inch thick, fastened to ceiling joists and wall studs or furring strips with either nails or screws. Caulk around windows, doors or other openings to seal any gaps.

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