QORVAN

What EPA Radon Zones Mean

EPA radon zones predict the potential for elevated indoor radon by area. Learn what Zone 1, 2 and 3 mean and why every home still needs testing.

Updated · 2 min read · By QORVAN Editorial Team · Reviewed by QORVAN Product Team

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The EPA divides US counties into three radon zones based on geology, soil characteristics and the indoor radon measurements available when the map was made.

ZonePrediction
Zone 1Highest potential for average indoor radon above the action level
Zone 2Moderate potential
Zone 3Lower potential

Why zones are only a starting point

A zone describes a county’s geology, not your house. Indoor radon depends on much more: the foundation type, the soil immediately beneath and around the building, cracks and penetrations, pressure differences created by heating and exhaust fans, and how the home is ventilated.

That is why the EPA’s own advice is unambiguous: test every home, whatever the zone. The map is useful for prioritising — and for understanding why a neighbour’s result may differ from yours.

Using the map well

  • Use it to decide when to test first, not whether to test.
  • Use it together with state guidance, which is often more granular and may include local building requirements.
  • If you are buying, the EPA recommends testing before purchase and asking about radon, as it does for other structural issues.
  • If you are in Zone 1 and never tested, testing is the highest-value next step you can take.

The EPA zone map is US-specific. Other countries publish their own radon potential maps and reference levels — check your national or regional guidance if you are outside the United States.

Frequently asked questions

Is radon worse in Zone 1?
Zone 1 counties have the highest predicted potential for elevated radon, but individual homes vary widely. Zone 3 areas still contain homes above the action level.
Should I test if I live in Zone 3?
Yes. The EPA recommends testing all homes below the third floor, regardless of zone.
Where do I find my zone?
The EPA publishes county-level zone maps, and most state radon programmes publish more detailed local information and guidance.

Sources

  1. EPA Map of Radon Zones — U.S. EPA
  2. A Citizen's Guide to Radon — U.S. EPA