The Rigid Foam Insulation Solution for Radiant Floor Heating

Image of ThermalStar® Below Grade Insulation. There are workers at the far end of the image wearing neon yellow shirts.


Radiant floor heating has become popular for new homes and corporate buildings for maximum comfort and clean living. They provide evenly distributed heat without noisy and unsightly ductwork. Heated flooring also helps improve air quality and creates an energy-efficient structure with significant long-term savings in energy usage.

In order to make radiant heated flooring run most effectively, below-grade insulation is also necessary for maximum heat retention. After all, you don’t want the heat generated by the radiant flooring system to escape before it has a chance to warm the structure.

There are several benefits and factors to consider when choosing the best below-grade insulation for radiant heated flooring. The experts at Atlas Molded Products understand the code requirements and can help determine which of their wide range of products will best fit the needs of your project.

Proper PSI

When purchasing below-grade insulation boards, you may notice there is a wide range of PSI options available. While this is common, it can be confusing to know which PSI option is best for the project.

The proper PSI level for the insulation depends on what is on top of it and how thick the slab is. You want to pick insulation that will not collapse or compress under the weight of the slab on top.

With their wide variety of products, Atlas can help determine the proper insulation type for your specific radiant heated flooring. Their rigid foam insulation boards come in a range of PSI levels and are designed to be installed under concrete slabs to meet continuous insulation standards.

R-Value Properties

Radiant heating components installed over below-grade insulation boards.


With radiant flooring, you’ll want to maintain a certain R-value level for maximum efficiency and to be code-compliant with the structure’s particular zone. This comes down to the choice of insulation material.

The different codes and requirements when it comes to R-value are dependent upon where the structure is built. There are two primary paths to code compliance: prescriptive and performance.

The prescriptive approach requires each individual element to meet minimally accepted standards, while the performance pathway anticipates and predicts energy usage against an acceptable baseline. The latter approach is more focused on the performance of the structure as a whole while the former approach is concerned with the effectiveness of individual elements.

Regardless of which approach you prefer, below-grade insulation boards will help meet and even exceed the requirements to establish energy code compliance.

It is also important to consider the insulation materials to anticipate long-term performance. A material like EPS made of 98% air with no extra gasses or blowing agents retains its efficiency and provides a stable R-value for the entire lifetime of the structure, unlike other materials whose R-values depreciate over time.

Minimal Moisture Retention

Below-grade insulation boards laid out in a warehouse.


A big factor that negatively affects the performance of insulation is moisture. If the insulation gets wet and does not dry out, the water will reduce the R-value and the effectiveness of the insulation decreases. Over extended periods of time, the R-value will be so reduced that the structure will no longer have the heating and cooling retention that was wanted in the first place.

Moisture build-up also creates a hazardous living environment, as it corrodes the structure and fuels mold growth.

It is important to get an insulation product that does not retain moisture and is quick to dry out. You also want to make sure your product has a superior field performance and not just rely on lab tests for proof of performance.

In real-life applications, studies have conclusively shown EPS insulation not only absorbs less water than XPS insulation, but it dries faster and more completely as well. EPS insulation outperforms XPS in the long term as its R-value remains stable and is less likely to be affected by the elements.

Extra Protection

Atlas Below Grade Insulation Board also includes integrated termite resistance. In areas with medium-to-heavy termite activity, our under-slab insulation products add an additional level of protection to prevent infestation.

When using other products in termite-heavy zones, either another protective solution needs to be implemented or the structure is left exposed. Atlas saw the opportunity to integrate this feature into our products to help save the time and costs of finding and alternative solutions.

Limited Lifetime Warranty

Atlas insulation products come with a limited lifetime warranty which covers both the physical and thermal properties. This also includes the termite resistance properties when available.

Having insulation backed by a warranty like this is key when trying to ensure that desired R-value retention long term.

For a detailed explanation of inclusions and limitations, please read the ThermalStar Limited Lifetime Warranty for terms and conditions.

Low Ozone and Global Warming Potential

Many homeowners want to create an energy-efficient home in order to minimize their environmental impact, and they seek out “green” products to help achieve this goal.

EPS is produced using pentane which has a very low global warming potential (GWP). By contrast, XPS often uses blowing agents that have a very high GWP. The gas also gradually escapes, reducing the R-value over time and decreasing energy efficiency.

Some manufacturers are testing alternative blowing agents for XPS insulation with a lower GWP, but the product is still not comparable to EPS.

Choose Atlas for Your Radiant Heated Flooring Insulation Needs

Stack of five white insulation foam boards


When it comes to quality and long-lasting insulation, you can rely on Atlas Below Grade Insulation Board to get the most out of your radiant floor heating.

Contact one of our representatives today to determine exactly what your needs are and how best to fulfill them.