How to insulate an existing concrete floor

Updated February 21, 2017

Existing concrete floors, like those found in most basements, can be cold if the floor has not been covered with carpet or insulated. If you plan to finish your basement or just want to provide a warmer floor, you can add a new sub-floor on top of the existing concrete. A new sub-floor can be constructed using rigid insulation and wood. Insulate existing concrete floors by first determining how much building material will be needed.

Remove all furniture from the floor so that it is completely clear. Clean up debris and dirt from the floor using a broom or a vacuum. Place polythene plastic sheets over the entire floor. Overlap the sheets by at least 3 inches. Place a strip of duct tape along the length of the seam. Cut the excess plastic with a utility knife.

Set pressure treated 2-by-4 inch boards along the perimeter of the basement flat side down. Use a tape measure to determine the lengths of 2-by-4 inch boards that will be needed. You can cut the 2-by-4 inch boards using a circular saw or mitre saw.

Secure the 2-by-4 inch boards to the concrete floor using a power actuated nail gun or ram set. Place a nail every 2 feet along the boards.

Set and secure 2-by-4 boards, flat side down, to create a grid pattern within the 2-by-4 perimeter. Use the tape measure to determine the length needed for the boards.

Place rigid foam insulation within the grid you created with the 2-by-4 inch boards. Cut the insulation to size using a circular saw, if necessary.

Set plywood sheeting on top of the grid of 2-by-4 inch boards. Measure the plywood with a tape measure; cut it to the needed size with the circular saw, if necessary. Secure the plywood sheeting to the 2-by-4 boards with screws using a power drill.


Apply carpet or other type of covering if you want to finish the floor.


You can damage your ears if you do not wear ear protection when using a power actuated nail gun.

Things You'll Need

  • 2-by-4 inch pressure-treated boards
  • Plywood sheeting
  • Power-actuated nail gun or ram set
  • Circular saw or mitre saw
  • Polythene plastic
  • 1-inch thick rigid foam insulation
  • Pencil
  • Duct tape
  • Utility knife
  • Power drill
  • Screws
  • Broom
  • Vacuum
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About the Author

Cameron Easey has over 15 years customer service experience, with eight of those years in the insurance industry. He has earned various designations from organizations like the Insurance Institute of America and LOMA. Easey earned his Bachelor of Arts degree in political science and history from Western Michigan University.