California Porch

California note · Home and property

Radon is checked with a test, not a guess

Testing is the only way to know a home's radon level; CDPH says real-estate transaction testing should use a certified tester.

radonhome testingindoor air

Radon is easy to miss because you cannot see or smell it. A map can show areas where radon has been found, but it cannot tell you the exact level in one living room, basement, or slab-on-grade house.

CDPH says testing is the only way to know. Homeowners can use a test kit or hire a certified tester; for a real-estate transaction, CDPH says to use a certified tester.

Do not treat one neighbor’s result like your own. Houses on the same street can test differently. EPA and CDPH strongly recommend fixing a home at 4 picocuries per liter or higher, and say to seriously consider action between 2 and 4. Use the official testing steps to confirm the result and find qualified mitigation help.

Where to see it

CDPH indoor radon pages and county or local environmental health information.

Official sources

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Reviewed July 14, 2026

California Porch explains the path. The official source is still the place to confirm the current rule, fee, form, map, deadline, or office decision.

Use the official page before you spend money, file paperwork, rely on a deadline, or change a property.

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