Insulating a Basement Floor

Insulating a basement floor requires a simple framework for the insulation. You will gain a more comfortable home environment, a mold-free basement and savings on your yearly energy bills.

Step 1 – Clearing the Basement

Remove all furniture and storage items that are located in the basement area. 

Step 2 – Checking the Floor

Be sure that the floor of your basement has no water issues. If there are water leak issues or plumbing problems, be sure to deal with those problems before you begin to do any insulating work. 

Step 3 – Sealing the Cement

Use a strong concrete sealer to seal the cement basement flooring. Check with a professional in your local hardware store for the best brand and type of sealant for your home improvement job. Use a push broom or wet/dry vacuum to remove all dust, dirt and debris from the concrete floor. When the floor is completely clean, pour the concrete sealer into the paint roller pan. Use a paint roller to roll a layer of the concrete sealer onto the concrete. Allow the sealer 24 hours to dry. Apply a second coat of sealer with the paint roller. Allow the second coat of concrete sealer 24 hours to dry thoroughly.

Step 4 – Laying the Plastic

Place sheets of polyethylene plastic onto the sealed concrete basement floor. The plastic sheets should overlap by three inches. Apply a strip of duct tape on the seam between the plastic sheets. Use a utility knife to cut off and remove any excess plastic.  

Step 5 – Building the Framework

Be sure the lumber you are using for the framework is pressure treated to prevent it from rotting over time. Place the two by four boards on the floor around the entire perimeter of the basement with the flat side facing down. Use a drill and three-inch masonry screws to secure the boards to the concrete floor. The screws should be secured every two feet. Place the boards 16 inches apart, between each end of the perimeter. When all of the boards have been placed onto the floor, the framework will look much like a grid. Secure the boards to the lumber around the perimeter of the basement floor.

Step 6 – Installing the Rigid Foam Insulation Boards

Install 1-1/2 inch thick rigid foam insulation into the spaces between the boards. Use 15-inch wide rigid foam boards. Cut the boards with a utility knife, to the necessary lengths. 

Step 7 – Covering the Insulation

Use tongue-and-groove plywood to cover the pretreated lumber and insulation boards. Use a drill and screws to secure the plywood to the frame. Secure the galvanized two-inch screws every eight inches along the plywood.