How to Insulate Existing Walls With Foam


Insulating the existing walls with foam will make your home more flame-retardant, reduce outside noise, and gives you big savings on your energy bill. Insulating your home with foam keeps you warm in the winter, cool in the summer, and adds value. Foam insulation can be added to your existing walls from the inside or outside through any surface including brick, vinyl siding, stucco, sheetrock or drywall. A hole is drilled through the wall surface and a tube is inserted, carrying the foam insulation inside the wall.

Things You'll Need

  • Safety glasses
  • Rubber gloves
  • Protective mask
  • Slow-rise spray foam kit for existing wall insulation
  • Drill with hole saw
  • Stud finder
  • Plastic straws
  • Foam saw
  • Unpack your slow-rise spray foam kit for existing wall insulation and read the directions thoroughly to understand how to set up and use the product.

  • Locate the stud in your wall with a stud finder. Drill holes between the studs equal to the size of tubing you will be using. Use a drill to make holes in the wall at the 3- and 6-foot level and 8 inches from the top of wall using a drill with a bit, or hole saw depending on the wall's internal or external surface.

  • Follow the directions that came with your foam insulation kit regarding how much foam to use and how long it will take to fill the wall. Insert the tube in the lowest hole in the wall and start the flow of foam insulation. Check the level of foam inside the wall by inserting a plastic straw in the holes above to see if the foam has reached that level. When the foam comes near the next hole up, remove the tube and insert it in the next hole drilled in the wall. Repeat this until the wall is insulated.

  • Scrape away the excess foam on interior and exterior walls with a foam saw. Excess foam insulation can be washed off with a hose on outside areas.

  • Patch the holes with proper substances for the wall surface you are working with. Paint or replace grout, vinyl siding, or stucco to finish the project.

Tips & Warnings

  • Foam insulation on existing walls can be done from the exterior or interior walls of the house. The procedure is the same for both. When drilling through a brick wall, drill through the grout only and replace the grout after the insulation procedure is finished. Patch the holes in drywall with joint compound, sand when dry, and paint. Reinforce loose or separating drywall with drywall screws.
  • Wear protective clothing, safety glasses, rubber gloves, and a protective mask when working with foam insulation. Avoid breaking, cracking, or damaging drywall by not overfilling the wall with foam insulation.


  • Photo Credit house image by Cora Reed from
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