CA California Porch

Almanac note · Home and property

Radon is checked with a test, not a guess

CDPH radon pages explain testing, maps, and follow-up steps for a gas that can vary from house to house.

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 has radon information for California, and EPA has national testing basics. A real test is the key step, especially during a home purchase, after major foundation work, or when a lower-level room becomes regular living space.

Do not treat one neighbor’s result like your own. Houses can test differently on the same street. If a test comes back high, the next step is follow-up testing or mitigation information from the official radon pages.

Where to see it

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

Official sources

Official source trail

Reviewed July 4, 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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