Ohio has significant radon risk across much of the state, with an estimated 46% of Ohio homes testing above 4.0 pCi/L according to the Ohio Department of Health. Ohio’s geology — including glacial till, black shale, and limestone formations — produces elevated radon potential across the northern and central portions of the state. The Ohio Department of Health estimates that over 2 million Ohio homes have elevated radon levels.
EPA Radon Zone Designation
Ohio is predominantly EPA Radon Zone 1. Most Ohio counties are Zone 1 or Zone 2. The highest-radon areas are concentrated in the glaciated portions of northwestern and north-central Ohio and the black shale formations in central Ohio. Southern Ohio counties in the Appalachian region tend toward Zone 2, though individual homes can exceed 4.0 pCi/L throughout the state.
Radon Contractor Licensing in Ohio
Ohio requires radon contractors to hold current NRPP or NRSB certification to legally perform radon measurement and mitigation services. Ohio’s radon certification program is administered by the Ohio Department of Health. The ODH maintains a list of certified radon professionals searchable by location. Contractors performing radon services in Ohio without current certification may be operating in violation of state requirements. Always verify certification status directly with the ODH before hiring.
Radon Disclosure Requirements in Ohio
Ohio’s real estate disclosure law requires sellers to disclose known material defects, and the Ohio residential property disclosure form includes a specific question about radon — asking whether the seller has received a radon test report and if so, what the results were, and whether a radon mitigation system is installed. Sellers who have received radon test results must disclose them. Ohio buyers routinely include radon contingencies in purchase offers.
Radon-Resistant New Construction (RRNC) in Ohio
Ohio does not have a statewide RRNC mandate for new construction. The Ohio Building Code does not require RRNC features as a standard provision in all jurisdictions. However, EPA strongly recommends RRNC for new Ohio construction, particularly in Zone 1 northern and central counties. Buyers of new construction should ask builders directly about RRNC inclusion. The IRC Appendix F provisions are available for local adoption, and some Ohio municipalities have incorporated RRNC requirements.
Highest-Radon Counties and Areas in Ohio
Ohio’s highest-radon areas include the glaciated till counties of northwestern and north-central Ohio (Defiance, Fulton, Henry, Williams, Wood counties in the northwest; Wyandot, Hancock, Crawford, Marion, Morrow, Knox in the north-central region) and the black shale formation counties of central Ohio including Delaware, Franklin, Licking, and Fairfield counties. The Ohio Geological Survey and Ohio Department of Health have published county-level radon data.
Testing Resources for Ohio Residents
The Ohio Department of Health administers the state radon program and provides resources for homeowners including lists of certified contractors, low-cost or free test kit programs (availability varies by year and funding), and technical guidance on radon mitigation. Contact the state radon program directly for the most current contractor list, any available test kit distribution programs, and jurisdiction-specific requirements that may have changed since this page was last updated.
Frequently Asked Questions
What percentage of Ohio homes have elevated radon?
The Ohio Department of Health estimates approximately 46% of Ohio homes test above the EPA action level of 4.0 pCi/L — representing over 2 million Ohio homes with elevated radon. Testing is strongly recommended for all Ohio homes.
Does Ohio require radon contractor certification?
Yes. Ohio requires radon contractors to hold current NRPP or NRSB certification. Verify credentials through the Ohio Department of Health radon program before hiring any contractor for testing or mitigation.
Does Ohio require RRNC for new construction?
No statewide mandate exists. EPA strongly recommends RRNC for new Ohio construction, particularly in Zone 1 areas. Buyers of new construction should ask builders whether RRNC features are included.
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