What do EPA radon Zones 1, 2 and 3 mean?

Short answer: EPA’s Map of Radon Zones puts each county in one of three zones by radon potential: in Zone 1, average indoor levels may be greater than 4 pCi/L; in Zone 2, between 2 and 4 pCi/L; in Zone 3, less than 2 pCi/L. It describes county geology, not your house. EPA says homes with elevated radon have been found in all three zones, so every home should be tested.

What the map is

EPA: "The Map of Radon Zones was developed in 1993 to identify areas of the U.S. with the potential for elevated indoor radon levels." It "was developed using data on indoor radon measurements, geology, aerial radioactivity, soil parameters, and foundation types." Zones are assigned county by county.

Zone 1, Zone 2, Zone 3

From EPA’s radon zones map legend:

  1. Zone 1 (red): "Highest potential; average indoor radon levels may be greater than 4 pCi/L" (picocuries per liter).
  2. Zone 2 (orange): "Moderate potential; average indoor radon levels may be between 2 and 4 pCi/L."
  3. Zone 3 (yellow): "Low potential; average indoor radon levels may be less than 2 pCi/L."

Why a zone is not a test result

EPA is direct about this: "The Map of Radon Zones should not be used to determine if individual homes need to be tested." The legend adds: "Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon."

EPA’s guidance on results: "Fix your home if your radon level is 4 picocuries per liter (pCi/L) ... or higher," and "Consider fixing if your level is between 2 and 4 pCi/L." A zone tells you what is typical for the county. Only a test tells you the level in your home.

What Ground Report checks here, and what it doesn’t

The free score checks:

  • The EPA radon zone for the county of a street address in any of the 50 states or DC, named as EPA’s Map of Radon Zones. Zones 1 and 2 show a finding with a recommendation to test. Zone 3 alone is shown as "Limited data" with EPA’s note that all homes should be tested.

It does not check:

  • The radon level inside your home. Ground Report does not measure radon, and no map can.
  • US territories. EPA’s map does not zone them.

Get a free score for a street address

Sources

Sources last reviewed 2026-10-26. Quotes are taken from the linked pages. This page is general information, not a home inspection, a water test or an official flood determination.

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