Before You Mitigate Radon, Consider Spray Foam Insulation

Research shows that closed-cell spray foam insulation creates a highly effective barrier against radon gas in both new and remodeled homes.

More than half of the United States has a problem with invisible radon gas in buildings. 

Exposure to radon in homes is especially dangerous to smokers, raising risks of lung cancer by about 20 percent over long exposure. Still unknown is whether it might increase the severity of Covid-19 symptoms.

It’s timely that some spray foam makers have pointed out that their product provides excellent resistance to radon gas entering the home in addition to its air sealing and insulative properties.


Many states have a high inherent risk of radon gas seepage, yet only about 15% of homes in these regions have active mitigation systems in place. Image: EPA

In the past, the common way of dealing with high radon indoors has been after-the-fact mitigation with mechanical ventilation (a fan), a dedicated pipe, and often the addition of polyethylene barrier over basements or crawl spaces.

But according to Maxime Duzyk, with Demilec’s technical department, spray foam offers a proactive, rather than reactive approach, and can work in both new and existing installations. 

For example, the company’s Heatlok Soya brand has a high compressive strength, and can be walked on by workers, making it unlikely to be damaged by workers during the installation of a slab or foundation. This reduces the human error aspect of mitigating radon. 

The foam also insulates the slab, reducing energy costs in the home, and finally, by removing the need for a 24-hour mechanical fan, it saves on both installation and operational costs. On average, a radon fan uses about 900 kW per year. That’s $204 per year in New York, where electricity costs average $.21 per kilowatt.


This installation of spray foam fits tightly around penetrations. It will seal out radon gas and be covered with the concrete slab, although foam can also go over an old slab, followed by a new layer of concrete. Image: Demilec

Editor’s note: Demilec is part of the Huntsman Corp, which also owns the well established Icynene-LaPolla brands of spray foam. They provided technical assistance and photography for this story.


How well does spray foam insulation stop radon gas? 

Studies of performance from Demilec, a Canadian spray foam maker, show that 32mm (1.25") of closed cell foam offers about 11 times more resistance to radon migration than 6-mil polyethylene. Advocates of spray foam note that because it expands to fill gaps and cracks, it is far easier to achieve high level radon resistance around plumbing and electrical penetrations.

How long does spray foam take to fully cure? 

Most foam makers suggest waiting 24 hours, after which the chemical reaction in the foam should be fully complete. Spray foam will absorb water, if pipes burst or a room is flooded, but the foam will also dry out once the source of moisture is removed, making it highly resistant to growing mold and mildew.

How much will it cost to mitigate radon with spray foam in my home?

Closed-cell foam will cost you about $1.50 per sq. ft. for 1-inch-thick foam in a 12” x 12” area. If your primary goal is radon resistance, you could get by with less than 2 inches of foam under your slab. Multiply the square footage of your basement and you have a ballpark estimate. 

Keep in mind that the foam will also reduce your heating/cooling costs and make any sub-ground space less likely to need dehumidification. You’ll also forego the cost of the radon mitigation fan and its operation.