Short answer
An EPA zone is a rating from 1 to 3 that EPA assigns to every U.S. county describing how much radon potential is predicted in that area, not the radon level in any specific building.
What EPA zone means
EPA drew the map to identify areas of the United States with the greatest potential for elevated indoor radon levels. It based the zones on indoor radon measurement data, geology, aerial radioactivity, soil parameters and foundation types.
The zone is a prediction for the whole county. Houses with elevated radon are found in all three zones.
The three zones in both units
Each row converts the zone's predicted average from
| Zone | EPA's description | Predicted average, pCi/L | In Bq/m³ |
|---|---|---|---|
| Zone 1 | Highest potential | Greater than 4 | Greater than 148 |
| Zone 2 | Moderate potential | Between 2 and 4 | Between 74 and 148 |
| Zone 3 | Low potential | Less than 2 | Less than 74 |
What it means for your home
Use the zone for context and a test for your home. A Zone 3 county does not clear a house, and a Zone 1 county does not condemn one.
The zone does change what a builder should do: EPA recommends building new homes with radon-resistant features in Zone 1 areas.
Where to go next
- Radon map of every U.S. county. Find a county's zone and the tests reported there.
- Where radon is most common. The states and regions where high results turn up most.