Radon Testing in California Real Estate Transactions

Radon testing during the inspection contingency period is the most practical time to assess a property for radon risk. A short-term radon test runs for a minimum of 48 hours using a continuous electronic radon monitor, with the monitor placed in the lowest livable level of the home — typically the first floor or crawlspace-level bedroom. Results are available within 1–2 days of monitor retrieval. If levels are at or above 4.0 pCi/L (the EPA action level), buyers can negotiate remediation before closing or request a price adjustment to cover future mitigation costs.

California does not currently require radon testing or disclosure for residential real estate transactions. Unlike some East Coast and Midwest states where radon disclosure is mandatory, California sellers are required to disclose only material facts they actually know. Most California sellers have never tested for radon and have no knowledge of their home's levels — so buyer-commissioned testing during escrow is the primary safety mechanism.

The EPA action level of 4.0 pCi/L is the threshold at which the agency recommends mitigation, estimating the lifetime lung cancer risk from continuous exposure at that level to be comparable to smoking eight cigarettes per day. The EPA also recommends considering mitigation at levels between 2.0–4.0 pCi/L, particularly for long-term homeowners. In practice, most buyers and their agents treat any result above 4.0 pCi/L as a condition requiring resolution before closing.

Bay Area radon levels vary significantly by location and soil type. Areas with certain geological formations — particularly those with higher uranium content in underlying bedrock — tend to produce more radon. However, radon risk cannot be predicted by zip code or neighborhood: adjacent homes on the same street can have dramatically different levels depending on foundation type, ventilation patterns, and soil composition beneath the specific slab. EPA's radon zone maps identify regional potential but should not be used as a substitute for property-specific testing.

Mitigation costs, when required, typically run $1,500–$3,500 for standard Bay Area installations. For buyers, this represents a known, manageable cost that can be negotiated as a closing condition. Systems are installed in a single day, are highly effective, and require minimal maintenance. Buyers who test and find elevated radon are in a strong negotiating position — the information is an asset, not a problem.