A Spray-Applied Alternative to Continuous Radon Barriers

Radon gas exposure remains a significant U.S. health risk. The Environmental Protection Agency estimates that indoor radon causes or contributes to 21,000 lung cancer deaths each year.

The 2018 International Residential Code for One- and Two-Family Dwellings (August 2017) defines radon as, “A naturally occurring, chemically inert, radioactive gas that is not detectable by human senses. As a gas, it can move readily through particles of soil and rock, and can accumulate under the slabs and foundations of home where it can easily enter into the living space through construction cracks and openings.”

Finished Basement Concern

The danger of indoor radon exposure must not be minimized. Cardiothoracic Surgeon Dr. Rick Thompson of Lincoln, Neb. says “Radon … actually deposits tiny little radioactive particles that you can’t see or touch in your lung tissue. Over time that accumulates and can actually mutate your lung cells.” Today’s growing trend to incorporate the basement, where heavier-than-air radon will accumulate, as bedroom, recreational, and entertainment space multiplies the concern of radon as a life-safety issue.

Radon Control Methods

The 2018 IRC offers several radon mitigation methods for jurisdictions that determine radon-resistant new construction is required through the use of locally available data or their Zone I designation (2018 IRC figure AF101 and Table AF101(1)). Structures built in a Radon Gas Pressure - Zone 1 are at highest risk for radon infiltration according to the EPA and the U.S. Geological Survey.

The 2018 IRC lists several methods for radon-resistance for four foundation types:

  • Subslab depressurization passive radon system
  • Passive radon system vented through sump pit
  • Passive radon system using drain tile loop
  • Submembrane depressurization system for crawl space
  • Polyethylene Sheet Barrier Method

Each of these system incorporates a soil-gas-retarder (2018 IRC AF103.3) – a continuous membrane of 6-mil (0.15 mm) polyethylene or other equivalent material used to retard the flow of soil gases into a building. Care must be taken to apply the polyethylene sheet so there are no coverage gaps or inadvertent punctures from the subfloor preparation (AF103.2). The subfloor preparation is a layer of gas-permeable material that is in direct contact with the ground. The material is a uniform layer of clean aggregate or sand note less than 4 inches thick, or “Other material, system or floor designs with demonstrated capability to permit depressurization across the entire subfloor area,” according to 2018 IRC AF103.2.

Spray Polyurethane Foam Barrier Method

In 2017 a spray polyurethane foam (SPF)-applied submembrane application method was introduced that offers homebuilders another soil-gas-retarder option. The SPF barrier option is compliant with ASTM E2178, the Standard Test Method for Air Permeance of Building Materials, and is radon gas-resistant based on ISO/IEC 17025-OL tests. A growing number of jurisdictions now recognize a SPF radon-barrier application as an accepted alternative to a continuous polyethylene sheet.

According to Demilec Inc., the SPF manufacturer, the minimum thickness of the SPF barrier is 32 mm (1 ¼-inch). An SPF barrier at that thickness not only offers radon resistance, but also insulation, air tightness, and vapor barrier characteristics.


Radon continues to represent an active hazard across hundreds of U.S. counties, especially in Radon Gas Pressure - Zone 1 jurisdictions. As you inspect new home construction, be aware some homebuilders may opt for a spray-applied SPF radon barrier as an alternative to a continuous polyethylene sheet.

To learn more about radon mitigation methods, reference the 2018 IRC, Appendix F – Radon Control Methods. The provisions in this appendix, like all appendices to the 2018 IRC for One- and Two-Family Dwellings, are not mandatory unless specifically referenced by your jurisdiction’s ordinance. To learn more about an SPF-applied radon barrier, review this brochure.

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The views and opinions expressed in this article are those of the Demilec and do not necessarily reflect those of the International Code Council, or Hanley Wood.




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