How to Put Foam Insulation in Existing Walls

Many older homes have no insulation in exterior walls, increasing heating costs. One solution is to add a spray foam insulation into the existing walls. It doesn't seem like it should be difficult. You drill a small hole in the wall between studs, insert the nozzle from a can of expanding spray insulation into the hole and fill the space with foam. However, cross braces between wall studs create at least two separate cavities between each set of studs, and each space must be filled with foam. This can lengthen the process, but it's still within the average homeowner's abilities.

Stud finder
Chalk
Drill with 1-inch hole saw
5/16- or 1/2-inch interior diameter tubing
Utility knife
Electrical tape
Foam insulation
Razor blade or other sharp blade
Plaster of Paris
Putty knife
100-grit sandpaper

Instructions

- 1
  Run a stud finder along your walls. When you locate one stud, keep in mind that in most houses additional studs will be approximately 16 inches apart. Make small chalk marks where the studs are.
- 2
  Measure halfway up the wall from the floor. This will be the approximate location of the cross brace between the studs. Cross braces are virtually impossible to find with a stud finder, so use this approximation method. Drill a 1-inch hole 6 inches below the vertical center of the wall, between two studs. This should place your hole just below the cross brace.
- 3
  Cut a 3- to 4-foot length of your tubing (the type of tubing used for fish tanks), using a utility knife. The exact interior diameter of your tubing will depend on the brand of foam insulation you are using -- check with the manufacturer for the proper size tubing.
- 4
  Attach one end of the cut piece of tubing to the foam tank and insert the other end into the 1-inch hole you cut in your wall. Insert the tubing so it goes almost all the way to the bottom of the wall cavity you are filling.
- 5
  Open the nozzle on the foam tank and fill the wall cavity approximately 1/10 to 1/3 full of foam, following the manufacturer's instructions. The foam will expand -- how much depends on the type of foam you buy. Allow the foam time to expand, according to the manufacturer's directions. If the foam has not expanded to the hole you drilled in the wall, add a small additional amount of foam until the expanded foam reaches the level of the hole.
- 6
  Drill another hole between the same two studs just under the top edge of the wall. Attach a new piece of cut tubing to the tank and insert the tubing into the new wall cavity, filling it as you did the first cavity.
- 7
  Go around the room, filling each wall cavity with foam. Keep in mind that cavities above and below windows and those above doors require considerably less foam.
- 8
  Scrape any foam that has come through your 1-inch holes with a sharp blade and then patch all holes with plaster of Paris or wall plaster repair. Use the blade of a putty knife to smooth the patch on the wall. When patches dry, sand lightly with 100-grit sandpaper.

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