How to Insulate a Closed Wall

By Chris Deziel

Upgrading your home's insulation is one of the most efficient ways to save energy. When constructing new homes, builders often staple fiberglass batts to the framing or spray in foam insulation, but neither method is possible if the walls are already covered. You can still insulate a closed wall, however, by spraying loose-fill insulation. The most efficient loose-fill products are made of cellulose soaked in a fire-retardant and provide insulation value comparable to fiberglass or foam. You blow loose-fill into a closed wall with an insulation blower, available for rental from most loose-fill insulation dealers.

List of Items Needed

  • Stud finder
  • Tape measure
  • Pencil
  • Insulation blower
  • Drill
  • Hole saw
  • Loose-fill insulation
  • Old newspaper
  • Can of spray foam insulation
  • Utility knife
  • Drywall joint compound
  • Drywall knife
  • Drywall tape
  • Wall primer
  • Paint
  1. Find the wall studs with a stud finder or by tapping on the wall and make a mark midway between each pair of studs with a pencil. The marks should be about 6 inches below the top of the wall.

  2. Rent an insulation blower and measure the diameter of the nozzle on the end of the hose. Using a hole saw with the same diameter, drill a hole centered on each mark you made on the wall. Save the cutouts for patching the holes when you are finished blowing.

  3. Fill the hopper of the blowing machine with loose-fill insulation and put on a dust mask to prevent you from inhaling insulation while you are blowing. Hold the nozzle in one of the holes, wrap a rag around it to prevent blow-back and turn on the machine.

  4. Allow the machine to run until it begins to sound like it is laboring, which is a signal that the section of the wall is almost full. Tap the wall a few times with a hammer to dislodge the material from pipes and electrical wires, and stop blowing when the level of the insulation reaches the bottom of the hole. Fill all the holes in the same way.

  5. Stuff some old newspaper into one of the holes for support, then spray in a little spray foam insulation from an aerosol can. As it is expanding, fit the cutout you removed back into the hole and adjust it so that it is flush with the wall. The foam will bulge out from the edges of the cutout.

  6. Cut the foam flush to the wall with a utility knife when it dries and coat the patch with drywall joint compound. Lay drywall tape on the joint compound and scrape the tape flat with a drywall knife. Let the compound dry, then spread a second coat and scrape it flat. Topcoat and scrape a third time if necessary. Paint the patch with primer and then the wall color.

Tips and Warnings

  • You can insulate an exterior wall by blowing from the outside. This usually involves removing siding, making holes in the plywood sheathing and replacing the siding when you are done.
  • Blowing insulation into your attic is another way to save energy. It makes your living space more comfortable by preventing heat from escaping through the roof.

© Demand Media 2011