Where to add basement insulation

You have two choices: Add insulation to your basement walls and treat the basement as indoor space, or add insulation to the basement ceiling and treat your basement as outdoor space. If you choose to treat your basement as outdoor space, you would close off all heating and cooling vents located in your basement—especially any vents on your furnace unit and on exposed HVAC ducts.

Add insulation to basement ceilings

Insulating your basement ceiling is a straightforward job. Use fiberglass batt insulation designed to fit between framing members. Figure a cost of $.50 to $2 per square foot to have a professional install 6 to 12 inches of fiberglass insulation.

Add insulation to basement walls

Though floor insulation is more common, wall insulation has advantages over ceiling insulation:

  • Efficiency—ceiling insulation often is compressed by many wires, pipes, and ducts that inhabit the floor joists, reducing effectiveness.
  • Gained living space—insulating basement walls usually makes basements more habitable and usable on a daily basis.

Adding insulation to your basement walls requires one of two basic methods:

Build and insulate a stud wall. This is an excellent method if you plan to use your basement as a living area, because the stud wall presents the opportunity to run electrical wiring and plumbing. Also, you’ll be able to cover the studs with drywall and create nicely finished wall surfaces.

For a stud wall, fill the stud cavities with regular fiberglass batt insulation. To prevent damage to the wall from trapped moisture, most building codes require installing a vapor barrier on the warmest (inside) side of the wall.

Install rigid foam sheathing directly against the basement wall. To prevent air infiltration and moisture problems, the seams between the rigid foam sheathing should be sealed with moisture-proof tape.

Codes often dictate that exposed foam sheathing be covered with an acceptable fire barrier, typically a layer of half-inch-thick drywall. Apply furring strips to the sheathing, then install a layer of drywall. Or, build a stud wall against the foam sheathing, fill the stud wall with unfaced fiberglass insulation, and cover with drywall. Both methods yield finished walls for your basement.