The Best Under Slab Insulation Options & How To Apply Them

Did you know that uninsulated foundations can result in 10 to 15% of a building’s total heat loss? Or that more than half of the energy consumption in U.S. homes can be attributed to heating and air conditioning?

Insulation can help improve the energy efficiency of your home and in turn, reduce your energy costs.

Here, we’ll share how under slab insulation can help you build a more comfortable and energy efficient home, explore the most common insulation options and provide a how-to guide for under concrete insulation.

Need under slab insulation? Contact us!

The Benefits Of Under Slab Insulation

Without insulation, the cold or heat from the ground can enter your home through the floor.

While it varies depending on your location, ground temperature throughout the U.S. is typically stable, ranging between 40 and 60 degrees Fahrenheit.

The issues that arise when you lack insulation come from the differences in inside and outside temperatures. The greater the temperature difference, the faster heat is able to transfer through your building slabs.

Why does this happen? 

Because concrete has the ability to hold heat and is more conductive compared to other building materials, like wood for example.

Heat and cold are transferred through the concrete slab as well as through slab edges. This can affect the temperature inside your home and may result in a number of issues, such as cold room temperatures, moisture, mold and even the nesting of unwanted pests.

The solution to these problems is rather simple: Under slab insulation.

This type of insulation can serve as a strong barrier against everything that may come into your home through the soil underneath, including toxic gases, unwanted creatures, cold temperatures and moisture.

Benefits include:

  • Improves moisture control in your home
  • Lowers energy bills
  • Provides compressive strength to help withstand heavy loads, giving the floor additional stability under heavy equipment and systems
  • Prevents toxic gases like radon from entering your home through the soil
  • Blocks freeze-thaw cycling and minimizes the possibility of cracking
  • Secures a healthy indoor environment without rodents, mold, moisture and toxic gases
  • Improves HERS index, which measures your home’s energy efficiency
  • Adds to sustainability
  • Reduces warranty calls

Types Of Insulation For Under Concrete Slab

The most common types of under slab or concrete insulation include rigid foam insulations, such as expanded polystyrene (EPS), extruded polystyrene (XPS) and radiant insulation, such as Prodex.

Let’s look at each type of insulation in more detail.

Expanded Polystyrene

  • Contains 98% trapped air and 2% plastic
  • Is produced by expanding spherical beads in a mold, then combining them with the help of heat and pressure
  • Has an average R-value of 3.6 per inch, which remains stable over a long period of time
  • Releases moisture quickly
  • Is typically white in color
  • Comes in various sizes and compressive strengths which ensures more flexibility

Extruded Polystyrene

  • Is produced from polystyrene crystals blended with additives and melted into liquid, then processed, expanded, shaped and cut
  • Has an average R-value of 4.7 per inch, which is lost over time because of its structure and production
  • Comes in blue, pink or green depending on the brand
  • Comes in standard dimensions in the shape of square or rectangular boards
  • Is more expensive than EPS


  • Is made of reinforced reflective foil and closed cell foam
  • Serves as an all-in-one solution for heat, cold and condensation
  • Is resistant to compression
  • Is resistant to moisture
  • Stops termites and other bugs
  • Blocks radon from penetrating your home
  • Is easy to install
  • Does not degrade over time
  • Seals well around nails
  • Is non-toxic

Reflective Bubble White Poly Insulation

An additional type of insulation you can use is reflective bubble white poly insulation. This insulation:

  • Consists of a polyethylene bubble center between a metalized low-emissivity surface on one side and a layer of polyethylene on the other side
  • Acts as a vapor retarder
  • Provides thermal break
  • Is easy to apply
  • Is white in color
  • Is very affordable

Not sure which type of insulation to use? Contact us!

How To Insulate Under Concrete Slab

You know the benefits of installing under concrete insulation, so now it's time to install.

For an easy, headache-free installation process, you can contact a professional insulation company to handle the job for you and ensure it’s installed correctly. However, if you decide to go it alone, you can follow our step-by-step installation guide.

To install under slab insulation:

  • Wait for dry, warm weather to install, to help reduce the moisture that can get trapped in the insulation.
  • Dig as deep as needed, depending on the type of construction.
  • Smooth the excavated ground and add dirt to fill in low spots.
  • Spread a layer of crushed stone/gravel over the dirt and make a gravel bed that is 8 inches deep to ensure enough moisture drainage under the slab.
  • If the soil in the region holds moisture, use drainage pipes that run through the gravel 4 inches below the top of the gravel bed.
  • Smooth and level the gravel so that no jagged edges stick up.
  • Install rigid foam panels across the foundation. To ensure maximum efficiency, make sure they lay flat.
  • Lay foam around the perimeter of the foundation to level it with the concrete after it is poured.
  • Leave a vapor barrier between the insulation and the gravel.
  • Apply additional insulation along the slab edges to prevent heat loss.
  • Add a non-permeable membrane around the entire perimeter to prevent insect infestation.
  • Create a gas barrier using three-layer insulation that includes two layers of low-density polyethylene and a center of high-density polyethylene. If your home is located in an area where industrial or chemical companies have operated, keep in mind that the soil may be polluted with radon or methane.
  • Ensure that everything is smooth before you pour the concrete.

The Best Under Slab Insulation: Prodex

Our expert recommendation for the best under slab insulation is Prodex. It’s a new-generation radiant floor insulation that meets all of the challenges of under slab insulation. It blocks cold, heat, moisture, mold and unwelcome creatures.

Thanks to its durable structure, Prodex is designed to withstand the weight of a concrete slab and the rigors of foot traffic. It is also resistant to compression under the load of the standard concrete floor systems.

Prodex protects against water damage, mold and mildew by blocking condensation, and it serves as an effective barrier against unwelcome critters and soil gases like radon.

The Best Type Of Prodex For Under Concrete Insulation

Under Concrete Prodex Total 5M is designed specifically for under slab applications with 4-inch slabs. Its ability to reduce heat loss makes it ideal as radiant heat floor insulation.

Benefits of Under Concrete Prodex include:

  • Thermal break
  • Durability
  • Air and vapor barrier
  • Radon barrier
  • Resistance to dampness and condensation in concrete
  • Resistance to mold and mildew
  • Resistance to termites and other bugs
  • Easy installation

Equipment Checklist

Installing Prodex under slab is a fast and easy process an does not require special equipment.

In addition to your roll of Prodex, you will need a utility knife or sharp scissors and under concrete tape.

The utility knife will come in handy to cut the insulation in desired sizes.

Under concrete tape comes in flexible packages of two or 24 rolls. The two rolls will serve 1,250 sq ft of insulation while the 24 rolls will be sufficient for 15,000 sq ft of insulation.

You can use under concrete tape as a closure system and vapor seal on thermal insulation and all exterior vapor barriers. It is resistant to temperatures that range between –10° F and 185° F, which makes it suitable for use in various climates and weather conditions.

How To Install Under Slab Insulation With Prodex

When you use Prodex, the insulation process is simple. Here’s how it works:

  • Unroll your Under Concrete Prodex Total with the white side facing up
  • Overlap the seams at 2 inches
  • Allow the material to climb the wall 6 inches
  • Seal the seams with under concrete tape
  • Install wire mesh and a piping system per the manufacturer’s recommendations
  • Pour and smooth the concrete

Want to try Prodex? Get in touch!

Key Takeaways On Under Slab Insulation

Depending on climate conditions in your region, your home can lose heat and cold through the building slabs.

Installing high-quality under concrete insulation will add to your potential energy savings and improve the environment inside your home. Under slab insulation will help block moisture, toxic gases, condensation, mold and mildew, and even unwanted pests from entering your home.

As insulation experts, we highly recommend Under Concrete Prodex Total to help protect your home.

Need insulation for your home? Request a quote!

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