Madison County is one of the most-tested parts of Alabama for radon, and the numbers explain why local inspectors bring it up. This page collects the public data on radon in Huntsville and Madison County, where it comes from, and what it means for your house. Each figure is linked to its source below.
EPA radon zone
On the EPA Map of Radon Zones, Madison County is in Zone 1, the highest-potential category. Zone 1 counties have a predicted average indoor screening level greater than 4 pCi/L. Neighboring Limestone County is also Zone 1, as are several other counties across the Tennessee Valley, including Jackson, Morgan, Lawrence, Lauderdale, and Colbert.
The EPA is clear about how to use the map: it was built in 1993 from indoor measurements, geology, aerial radioactivity, soil data, and foundation types to help target programs and building codes. It is not meant to tell any individual whether to test. Homes with high radon have been found in all three zones.
Alabama Department of Public Health
The Alabama Department of Public Health identifies 15 counties with the highest potential for elevated radon: Calhoun, Clay, Cleburne, Colbert, Coosa, Franklin, Jackson, Jefferson, Lauderdale, Lawrence, Limestone, Madison, Morgan, Shelby, and Talladega. ADPH's radon program also offers information on testing and on finding certified professionals, and it points residents toward providers listed with the national certification programs.
Local test results
The American Lung Association's 2022 radon testing report for Alabama, built from CDC Environmental Public Health Tracking data, lists Madison County with 5,178 tests and a mean of 4.0 pCi/L, with about one in four tests (25.2%) at or above 4 pCi/L. Those are results from homes that chose to test, often during home sales, so they aren't a random sample. Still, a county average that sits right at the EPA action level is unusual and worth taking seriously.
The geology underneath
The U.S. Geological Survey's geologic radon assessment for EPA Region 4, which covers Alabama and Tennessee, ties radon potential to bedrock and the soils formed from it. North Alabama's Tennessee Valley and Highland Rim are underlain largely by limestone and other carbonate rocks. Soils that weather from these rocks can concentrate uranium and its decay products, and karst features such as fractures, solution channels, and caves give soil gas easy paths to move. That geology is a big part of why the Tennessee Valley counties stand out on Alabama's radon maps.
Local conditions vary a lot. The thick red clay soils common across Madison County can slow gas movement in some spots and channel it through cracks in others. Mountain-side homes on Monte Sano or Green Mountain, valley homes in south Huntsville, and newer subdivisions in Madison and Harvest all sit on different ground. This is why two houses on the same street can test differently.
What it means for your home
- Test, regardless of the neighborhood. A Zone 1 rating and a 4.0 county mean raise the odds, but only a test tells you about your house.
- Test the lowest lived-in level. Basements and ground-floor bedrooms over crawl spaces usually read highest.
- New homes aren't exempt. Tight construction can trap radon. Unless a builder installed a radon-resistant system, and many don't, new houses should be tested like any other.
- High results are fixable. Active soil depressurization reliably lowers indoor radon in most homes. See mitigation systems.
Licensing in Alabama
Alabama has no state law licensing radon testers or mitigators. That makes national certification the most useful quality check. Ask whether a provider is listed with the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB), and verify it on their websites.