Radon zones in California
Last updated
EPA’s Map of Radon Zones places 58 California counties in its three radon potential zones: 2 in Zone 1 (highest), 29 in Zone 2 (moderate), and 27 in Zone 3 (low).
What this means for California homes
Most California counties fall in Zone 2. EPA predicts moderate average indoor levels (2 to 4 pCi/L) across much of California. Many homes will be below the action level, but many will not, and only a test can tell which.
EPA’s guidance is the same everywhere: test your home, fix it if the level is 4 pCi/L or higher, and consider fixing between 2 and 4 pCi/L. The zone map is from 1993 and should not be used to decide whether a single home needs testing.
California radon program
EPA lists the following state contact for California: CA Indoor Radon Program, phone 916-449-5674. Website: www.cdph.ca.gov/radon. State programs can tell you about local testing data, free or discounted test kits, disclosure rules for home sales, and credentialed radon professionals.
California counties and their EPA radon zones
County names follow the 2020 Census. Zones from the EPA Map of Radon Zones (text version). Rows marked “zone of” use the zone EPA gave the predecessor or surrounding county.
Next steps: read how to test your home, check a result with the level calculator, or look up a single address by ZIP code.