Appendix BE — RADON CONTROL METHODS
BE101 Scope — 2025 California Residential Code
California Residential Code (Title 24, Part 2.5) · 2025 edition · updated 2026-10-19 · California
CBSC: official editions, supplements and errata
Italicized text is a California amendment to the model code, as printed in the official publication.
Cite as: 2025 California Residential Code (Title 24, Part 2.5) § BE101 · Effective January 1, 2026 · Official source: Building Standards Commission
BE101.1 General.¶
This appendix contains requirements for new construction in jurisdictions where radon-resistant construction is required.
Inclusion of this appendix by jurisdictions shall be determined through the use of locally available data or determination of Zone 1 designation in Figure BE101.1 and Table BE101.1.
FIGURE BE101.1—EPA MAP OF RADON ZONES
a. pCi/L stands for picocuries per liter of radon gas. The US Environmental Protection Agency (EPA) recommends that homes that measure 4 pCi/L and greater be mitigated. The EPA and the US Geological Survey have evaluated the radon potential in the United States and have developed a map of radon zones designed to assist building officials in deciding whether radon-resistant features are applicable in new construction. The map assigns each of the 3,141 counties in the United States to one of three zones based on radon potential. Each zone designation reflects the average short-term radon measurement that can be expected to be measured in a building without the implementation of radon-control methods. The radon zone designation of highest priority is Zone
- Table BE101.1 lists the Zone 1 counties illustrated on the map. More detailed information can be obtained from state-specific booklets (EPA-401-R-93-021 through 070) available through the State Radon Offices or from the EPA Regional Offices.
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