Insulating Beneath the Basement Slab

Keep heat in and keep moisture out with an insulation layer under your home.
TS-87699021_house-foundation_s3x4

TS-87699021_house-foundation_s3x4

House foundation

Photo by: Hemera Technologies

Hemera Technologies

Think of the surprise and delight a new homeowner would have to find that their basement is not only usable space, but warm and comfortable as well. By taking a few extra steps, builders can toss out the notion that basements are cursed to be dank, cold and musty storage rooms.

Most basements are built in direct contact with the cold, moist ground. Concrete will absorb moisture, like a sponge, and the result is an uncomfortable, musty living space. The additional water introduced into the home can also lead to mold issues. Finding a way to keep water out of the basement will greatly improve the smell and health of the home.

Heat is also lost through the basement floor. The notion that heat always rises isn't entirely true. Heat will flow toward relatively cooler places. If ground under the home is cooler than the basement temperature, which is the case in almost every climate year round, heat will naturally try to escape through the concrete slab.

Creating an insulation layer and a vapor barrier between the concrete slab and the ground beneath it is the best practice in insulating basement floors. The insulation barrier will help keep warm air in, and the vapor barrier will keep unwanted moisture out.

Here's how to do it:

  • Evenly spread the base gravel under the basement slab, keeping it 1 inch lower than the conventional method.
  • Place a 1-inch layer of 4'x8' extruded polystyrene foam board over the gravel, covering the entire floor area.
  • Tape the joints between the boards with builder's tape; you want to create a tight insulation layer.
  • Place 5 mil. polyethylene sheets over the foam board, overlapping at least 6 inches at the seam. Make sure there are no gaps, tears, or holes in the sheets and repair any you find with builder's tape. This covering will act as the vapor barrier.
  • Tape the joints with builder's tape and pour concrete as normal.

Keep Reading

Next Up

Cellulose Insulation

Because cellulose insulation is produced using recycled waste materials, it's a good option for environmentally conscious consumers.

Installing Fiberglass Batt Insulation

Use these tips and techniques to ensure proper installation of fiberglass insulation.

Spray Foam Improves on Insulation

Foam keeps heat in by sealing cracks and spaces in your house.

Basement Insulation Options and Solutions

Whether your basement is finished or not, proper insulation is important for temperature control and the prevention of moisture. Choose a basement insulation option that is best suited for your home and budget.

Choosing Insulation

There are more options for your addition than those rolls of pink fiberglass

Insulating Basement Walls

Basement insulation comes in a multitude of materials, making the installation process unique to each home. Learn more about what will work for your basement with this guide.

Insulating a Basement Ceiling

Wires and pipes that line a basement ceiling can make installing insulation difficult. Take these precautions to get the job done without disruption.

Insulating Attic Access

Learn how to fill up attic spaces effectively.

Garage Insulation Basics

Adding insulation to a garage is the easiest do-it-yourself job in a renovation or new build.

Insulating a Basement Floor

Make your finished basement warm and inviting by installing floor insulation.

Follow Us Everywhere

Join the party! Don't miss HGTV in your favorite social media feeds.