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Illinois has significant radon risk, with an estimated 35–40% of Illinois homes testing above the EPA action level of 4.0 pCi/L. The Illinois Emergency Management Agency (IEMA) Radon Section estimates that radon may be responsible for approximately 1,000 lung cancer deaths in Illinois annually — more deaths than are caused by drunk driving. Illinois has enacted some of the more comprehensive radon legislation in the Midwest, including contractor licensing requirements and school radon testing mandates.

EPA Radon Zone Designation

Illinois is predominantly EPA Radon Zone 1. Illinois counties range from Zone 1 in northern and central Illinois to Zone 2 in the southern portion of the state. The highest-radon areas are concentrated in the glaciated portions of northern and central Illinois where glacial till deposits overlie uranium-bearing geology. Northern Illinois counties in the Chicago metropolitan area and central Illinois agricultural counties show the highest average readings.

Radon Contractor Licensing in Illinois

Illinois has a comprehensive radon contractor licensing program. Illinois law requires radon contractors — both for measurement and for mitigation — to hold an Illinois state radon contractor license issued by the Illinois Emergency Management Agency. Illinois licensing requires passing state-approved training, holding NRPP or NRSB certification, carrying liability insurance, and paying licensing fees. Illinois maintains a searchable database of licensed radon contractors at iema.illinois.gov/radon. Performing radon measurement or mitigation without an Illinois radon license is a violation of Illinois law.

Radon Disclosure Requirements in Illinois

Illinois has enacted specific radon disclosure requirements for real estate transactions. Illinois law requires sellers of residential property to disclose known radon test results to buyers. Illinois uses a Residential Real Property Disclosure Act that includes radon — sellers must indicate whether they have received a radon test report and provide the report to buyers if one exists. Illinois also requires IEMA-approved radon pamphlets to be provided in certain transactions. Additionally, Illinois law requires radon testing in all public schools and mandates school radon disclosure to parents.

Radon-Resistant New Construction (RRNC) in Illinois

Illinois does not have a statewide RRNC mandate for new residential construction. However, the IEMA Radon Section strongly recommends RRNC for new construction in Illinois, particularly in Zone 1 northern and central counties. Some Illinois municipalities — particularly in the Chicago metropolitan area — have incorporated RRNC requirements locally. Buyers of new construction should ask about RRNC inclusion, especially in northern Illinois.

Highest-Radon Counties and Areas in Illinois

Illinois’s highest-radon areas are in the glaciated northern and central counties. The Chicago metropolitan area counties — Cook, DuPage, Kane, Lake, McHenry, Will, and Kendall — have elevated average radon levels. Central Illinois agricultural counties — including McLean, Tazewell, Peoria, Sangamon, and Champaign — also show significant radon levels. Southern Illinois counties generally have lower but still meaningful radon levels. IEMA publishes county-level radon data from the Illinois Radon Monitoring Program.

Testing Resources for Illinois Residents

The Illinois Emergency Management Agency (IEMA) Radon Section 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

Does Illinois require radon contractor licensing?

Yes. Illinois has one of the more comprehensive radon contractor licensing programs in the nation. Both measurement and mitigation contractors must hold an Illinois state radon license issued by IEMA, in addition to NRPP or NRSB national certification. Verify license status at iema.illinois.gov/radon.

Does Illinois require radon disclosure when selling a home?

Yes. Illinois law requires sellers to disclose known radon test results to buyers under the Residential Real Property Disclosure Act. If a radon test report exists, it must be provided to buyers.

Does Illinois require radon testing in schools?

Yes. Illinois law requires radon testing in all Illinois public schools. Results must be disclosed to parents. Illinois is among the states with the most comprehensive school radon testing mandates in the U.S.

Michigan has significant radon risk across much of the state, with an estimated 30–35% of Michigan homes testing above the EPA action level of 4.0 pCi/L. The Michigan Department of Environment, Great Lakes, and Energy (EGLE) estimates that radon may contribute to hundreds of lung cancer deaths in Michigan annually. Michigan’s geology — including granitic basement rock in the Upper Peninsula, glacial till and outwash across both peninsulas, and limestone formations in the Lower Peninsula — creates varied but often significant radon potential.

EPA Radon Zone Designation

Michigan is predominantly EPA Radon Zone 1. Michigan counties range from Zone 1 in parts of the Upper Peninsula and northern Lower Peninsula to Zone 2 in much of the southern Lower Peninsula. The Upper Peninsula counties overlying granitic basement rock tend to have higher radon potential. Northern Lower Peninsula counties in the glaciated sand and gravel deposits also show elevated levels.

Radon Contractor Licensing in Michigan

Michigan requires radon contractors to hold current NRPP or NRSB national certification. Michigan’s radon program is administered through the Michigan Department of Environment, Great Lakes, and Energy (EGLE). Michigan does not have a separate state radon contractor licensing statute — national certification through NRPP or NRSB is the operative requirement. EGLE maintains resources on radon and certified professionals. Verify contractor credentials at nrpp.info or nrsb.org before hiring.

Radon Disclosure Requirements in Michigan

Michigan’s real estate disclosure law requires sellers to complete a Seller’s Disclosure Statement disclosing known defects and conditions. The Michigan disclosure form includes questions about radon — specifically whether the property has been tested and what the results were, and whether a radon mitigation system is installed. Sellers must disclose known radon test results. Radon testing is standard practice in Michigan real estate transactions, particularly in northern Michigan and Upper Peninsula properties.

Radon-Resistant New Construction (RRNC) in Michigan

Michigan does not have a statewide RRNC mandate for new residential construction. The Michigan Building Code does not require RRNC features statewide. EGLE recommends RRNC for new construction in Zone 1 areas. The IRC Appendix F provisions are available for local adoption. Some Michigan municipalities have incorporated RRNC requirements locally. Buyers of new construction should ask builders about RRNC, particularly in northern Michigan and Upper Peninsula locations.

Highest-Radon Counties and Areas in Michigan

Michigan’s highest-radon areas include Upper Peninsula counties overlying granitic and iron-bearing bedrock: Marquette, Iron, Baraga, Houghton, Keweenaw, and Ontonagon counties. Northern Lower Peninsula counties with glacial sand and gravel deposits — including Kalkaska, Crawford, Roscommon, and Ogemaw counties — also show elevated levels. The EGLE publishes county-level radon data from testing surveys conducted across the state.

Testing Resources for Michigan Residents

The Michigan Department of Environment, Great Lakes, and Energy (EGLE) 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

Does Michigan require radon disclosure in real estate?

Yes. The Michigan Seller’s Disclosure Statement requires sellers to disclose known radon test results and the presence of any mitigation system. Sellers with knowledge of elevated radon levels must include this in their disclosure.

What parts of Michigan have the highest radon?

Upper Peninsula counties overlying granitic bedrock — particularly Marquette, Iron, Baraga, Houghton, and Keweenaw counties — have the highest radon potential. Northern Lower Peninsula counties with glacial sand and gravel also show elevated levels.

Does Michigan require radon contractor certification?

NRPP or NRSB national certification is required. No separate Michigan-specific licensing statute exists. Verify credentials at nrpp.info or nrsb.org before hiring any radon contractor.

Wisconsin has significant radon risk across much of the state, with an estimated 30–40% of Wisconsin homes testing above the EPA action level of 4.0 pCi/L. The Wisconsin Department of Health Services estimates that radon may be responsible for over 600 lung cancer deaths in Wisconsin annually. Wisconsin’s geology — including granitic bedrock in the northern shield area, glacial till across the state, and limestone formations in the southwestern driftless area — creates varied but often significant radon potential.

EPA Radon Zone Designation

Wisconsin is predominantly EPA Radon Zone 1. Most Wisconsin counties are Zone 1 or Zone 2. The highest-radon areas tend to be in the northern Wisconsin shield counties where granitic bedrock is close to the surface, and in the central sand plain counties where glacial outwash creates radon transport pathways. Southern Wisconsin counties overlying carbonate rock also show elevated levels.

Radon Contractor Licensing in Wisconsin

Wisconsin requires radon contractors to hold current NRPP or NRSB national certification to perform radon measurement and mitigation services. Wisconsin’s radon program is administered through the Wisconsin Department of Health Services. Wisconsin does not have a separate state-specific radon contractor licensing statute — national certification is the operative requirement. The WDHS maintains resources and information on certified professionals. Verify contractor credentials at nrpp.info or nrsb.org before hiring.

Radon Disclosure Requirements in Wisconsin

Wisconsin’s real estate disclosure law requires sellers to complete a Real Estate Condition Report disclosing known defects and conditions. The Wisconsin Real Estate Condition Report includes questions about environmental conditions including whether the property has been tested for radon and the results of any such tests, and whether a radon mitigation system is present. Sellers with knowledge of radon test results must disclose them. Radon testing is common in Wisconsin real estate transactions, particularly in high-radon areas.

Radon-Resistant New Construction (RRNC) in Wisconsin

Wisconsin does not have a statewide RRNC mandate for new residential construction. The Wisconsin Uniform Dwelling Code does not require RRNC features statewide. However, Wisconsin DHS recommends RRNC for new construction in Zone 1 areas. The IRC Appendix F provisions are available for local adoption. Some Wisconsin municipalities have incorporated RRNC requirements. Buyers of new Wisconsin construction should ask builders about RRNC inclusion.

Highest-Radon Counties and Areas in Wisconsin

Wisconsin’s highest-radon areas include the northern shield counties where granitic bedrock is prevalent: Iron, Ashland, Bayfield, Douglas, and Vilas counties. The glaciated central Wisconsin sand plain counties (Adams, Portage, Waushara, Waupaca, Marathon) also show elevated levels. The Milwaukee metropolitan area (Milwaukee, Waukesha, Ozaukee, Washington counties) spans the transition between Zone 1 and Zone 2 areas. The Wisconsin DHS publishes county-level radon data from testing surveys.

Testing Resources for Wisconsin Residents

The Wisconsin Department of Health Services 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

Does Wisconsin require radon disclosure when selling a home?

Yes. The Wisconsin Real Estate Condition Report requires sellers to disclose known radon test results and the presence of any radon mitigation system. Sellers with knowledge of elevated radon must disclose it.

What parts of Wisconsin have the highest radon?

Northern Wisconsin shield counties — Iron, Ashland, Bayfield, Douglas, Vilas — have the highest radon potential due to granitic bedrock. Central Wisconsin sand plain counties and parts of southern Wisconsin with carbonate geology also show elevated levels.

Does Wisconsin require radon contractor certification?

NRPP or NRSB national certification is required for radon professionals in Wisconsin. No separate state licensing statute exists. Verify credentials at nrpp.info or nrsb.org before hiring.

South Dakota has the third-highest average indoor radon level of any U.S. state, estimated at approximately 7.3 pCi/L statewide. The South Dakota Department of Agriculture and Natural Resources estimates that approximately 60% of South Dakota homes have radon levels above 4.0 pCi/L. South Dakota’s geology — including granitic rock in the Black Hills, glacial till across the east, and uranium-bearing formations — creates some of the highest radon potential in the nation.

EPA Radon Zone Designation

South Dakota is predominantly EPA Radon Zone 1. All South Dakota counties are Zone 1. The Black Hills region in western South Dakota overlies some of the most uranium-rich geology in the U.S., including formations associated with historic uranium mining. Eastern South Dakota counties in the glaciated plains also show consistently high radon levels.

Radon Contractor Licensing in South Dakota

South Dakota requires radon contractors to hold current NRPP or NRSB national certification. The South Dakota Department of Agriculture and Natural Resources administers the state radon program. South Dakota does not have a separate state radon contractor licensing law — national certification is the operative requirement. Verify contractor credentials at nrpp.info or nrsb.org before engaging any radon professional.

Radon Disclosure Requirements in South Dakota

South Dakota’s real estate disclosure requirements under general property disclosure law require sellers to disclose known material defects. South Dakota does not have a radon-specific disclosure statute. However, given that 60% of South Dakota homes exceed the EPA action level, radon is a significant known risk that sellers should address in disclosures when they have knowledge of test results. Real estate agents in South Dakota routinely recommend radon testing during the inspection period.

Radon-Resistant New Construction (RRNC) in South Dakota

South Dakota does not have a statewide RRNC mandate. Given the state’s Zone 1 designation across all counties and one of the nation’s highest average radon levels, EPA and SDANR strongly recommend RRNC for all new South Dakota residential construction. Buyers of new construction — particularly in the Black Hills region and eastern glaciated counties — should request RRNC inclusion in construction contracts.

Highest-Radon Counties and Areas in South Dakota

The Black Hills counties of western South Dakota (Lawrence, Pennington, Custer, Fall River, Meade, Butte) have some of the highest radon potential in the state due to uranium-bearing granitic geology. Eastern South Dakota counties in the glaciated plains — including Minnehaha (Sioux Falls area), Lincoln, Turner, and Lake counties — also show consistently high average readings. The SDANR publishes county-level radon survey data.

Testing Resources for South Dakota Residents

The South Dakota Department of Agriculture and Natural Resources 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

How high is radon in South Dakota?

South Dakota has the third-highest average indoor radon level in the U.S. — approximately 7.3 pCi/L. About 60% of South Dakota homes exceed the EPA action level. All 66 counties are Zone 1.

Does South Dakota require radon contractor certification?

NRPP or NRSB national certification is required. No separate state licensing law exists. Verify credentials at nrpp.info or nrsb.org before hiring.

Is the Black Hills area particularly high in radon?

Yes. The Black Hills counties have some of the highest radon potential in South Dakota due to uranium-bearing granitic formations. Lawrence, Pennington, Custer, and Fall River counties are among the highest-radon areas in the state.

North Dakota has the second-highest average indoor radon level of any U.S. state, estimated at approximately 8.2 pCi/L statewide. The North Dakota Department of Environmental Quality estimates that approximately 65% of North Dakota homes have radon levels above 4.0 pCi/L. North Dakota’s geology — including glacial lake sediments, shale, and uranium-bearing lignite formations — creates extremely high radon potential across the entire state.

EPA Radon Zone Designation

North Dakota is predominantly EPA Radon Zone 1. All North Dakota counties are Zone 1 — the highest radon potential designation. The uniform Zone 1 designation reflects the consistent geology of glacial deposits and shale formations across the entire state. No county in North Dakota has a Zone 2 or Zone 3 designation.

Radon Contractor Licensing in North Dakota

North Dakota requires radon contractors to hold current NRPP or NRSB national certification to perform radon services in the state. The North Dakota Department of Environmental Quality administers radon program resources and maintains information on certified professionals. North Dakota does not have a separate state radon contractor licensing statute independent of national certification. Verify contractor credentials at nrpp.info or nrsb.org before hiring any radon professional.

Radon Disclosure Requirements in North Dakota

North Dakota’s real estate disclosure law requires sellers to disclose known material defects. While North Dakota does not have a radon-specific disclosure statute, the general material defect disclosure duty covers known elevated radon conditions. Given that approximately 65% of North Dakota homes exceed the EPA action level, radon testing is standard practice in North Dakota real estate transactions. Buyers should include radon contingencies in all purchase offers.

Radon-Resistant New Construction (RRNC) in North Dakota

North Dakota does not have a statewide mandate requiring RRNC for all new construction. However, given the state’s extreme radon prevalence with all counties in Zone 1 and an average exceeding twice the EPA action level, EPA and NDDEQ strongly recommend RRNC for all new North Dakota residential construction. All new homes in North Dakota should include passive RRNC features per AARST-ANSI RRNC-2022 at minimum.

Highest-Radon Counties and Areas in North Dakota

All 53 North Dakota counties are Zone 1 with high radon potential. The highest average readings have historically been documented in western North Dakota counties overlying oil-bearing shale formations (Divide, Burke, Mountrail, McLean, Mercer, Oliver, Morton, Grant, Emmons counties) and in central North Dakota where glacial lake bed sediments from prehistoric Lake Agassiz are present (Cass, Ransom, Richland, Sargent counties in the east).

Testing Resources for North Dakota Residents

The North Dakota Department of Environmental Quality 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

How high is radon in North Dakota?

North Dakota has the second-highest average indoor radon level in the U.S. — approximately 8.2 pCi/L statewide. About 65% of North Dakota homes exceed the EPA action level of 4.0 pCi/L. All 53 counties are designated EPA Zone 1.

Does North Dakota require radon contractor certification?

NRPP or NRSB national certification is required. There is no separate North Dakota-specific licensing statute. Verify credentials at nrpp.info or nrsb.org before hiring.

Should every North Dakota home be tested for radon?

Yes — emphatically. With 65% of homes above the EPA action level and all counties in Zone 1, every North Dakota home should be tested. The question in North Dakota is not whether radon is likely to be present, but how high the level is.

Montana has among the highest radon levels in the western United States, with an estimated statewide average around 5.7 pCi/L and approximately 45% of Montana homes testing above the EPA action level. Montana’s geology — including granitic batholiths, uranium-bearing rock formations, and glacial deposits — creates high radon potential across much of the state. Every Montana county is designated Zone 1 or Zone 2 by EPA.

EPA Radon Zone Designation

Montana is predominantly EPA Radon Zone 1. Most Montana counties are Zone 1. The highest-radon areas are concentrated in western Montana where granitic rock formations (including the Boulder, Idaho, and Bitterroot batholiths) produce significant uranium and radon. Central Montana counties overlying shale formations also show elevated levels.

Radon Contractor Licensing in Montana

Montana requires radon contractors to hold current NRPP or NRSB national certification. Montana’s radon program is administered through the Montana Department of Environmental Quality. Montana does not have a separate state radon contractor licensing statute beyond the national certification requirement. The DEQ provides resources on radon testing and maintains information on certified professionals. Verify contractor credentials directly at nrpp.info or nrsb.org.

Radon Disclosure Requirements in Montana

Montana’s real estate disclosure requirements include the Montana Residential Property Disclosure Act, which requires sellers to disclose known material defects. Elevated radon is a known material condition that sellers should disclose under this general duty. Montana does not have a radon-specific disclosure statute, but the standard Montana real estate disclosure form includes questions about environmental conditions. Buyers should include radon contingencies in purchase offers and conduct independent testing.

Radon-Resistant New Construction (RRNC) in Montana

Montana does not have a statewide RRNC mandate for new construction. However, given Montana’s high radon prevalence and Zone 1 designation across most of the state, EPA and MDEQ strongly recommend RRNC for all new Montana residential construction. Some Montana municipalities may have adopted local RRNC requirements. Buyers of new Montana construction should request RRNC features — the incremental cost during construction is minimal compared to post-construction remediation.

Highest-Radon Counties and Areas in Montana

Western Montana counties overlying granitic batholiths have the highest radon levels in the state: Missoula, Ravalli, Mineral, Sanders, and Powell counties in the western region. Cascade County (Great Falls) and Lewis and Clark County (Helena) in central Montana also show elevated levels. The MDEQ publishes county-level radon data from testing surveys.

Testing Resources for Montana Residents

The Montana Department of Environmental Quality 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

Is Montana a high-radon state?

Yes. Montana has among the highest radon levels in the western U.S., with an estimated average of 5.7 pCi/L and approximately 45% of homes above the EPA action level. All Montana residents should test their homes.

Does Montana require radon contractor licensing?

Montana requires NRPP or NRSB national certification. There is no separate Montana-specific licensing. Verify contractor credentials at nrpp.info or nrsb.org before hiring.

What parts of Montana have the highest radon?

Western Montana counties overlying granitic batholiths — including Missoula, Ravalli, Mineral, Sanders, and Powell counties — have the highest concentrations. Central Montana counties also show elevated levels.

Indiana has significant radon risk across much of the state, with an estimated 35–40% of Indiana homes testing above the EPA action level of 4.0 pCi/L. Indiana’s geology — including glacial till deposits from the last ice age across much of the northern and central state, and Devonian black shale in parts of the state — creates elevated radon potential. The Indiana State Department of Health estimates that radon may be responsible for a significant portion of lung cancer deaths in Indiana annually.

EPA Radon Zone Designation

Indiana is predominantly EPA Radon Zone 1. Indiana counties range from Zone 1 in the northern glaciated portion of the state to Zone 2 in central Indiana and Zone 2-3 in southern Indiana. The highest-radon areas are generally in the northern counties where glacial till deposits are thickest and the geology most radon-productive.

Radon Contractor Licensing in Indiana

Indiana requires radon contractors to hold current NRPP or NRSB national certification. Indiana does not have a separate state-specific radon contractor licensing statute — national certification through NRPP or NRSB serves as the operative credential for professional radon work in Indiana. The Indiana State Department of Health maintains information on certified radon professionals and the state radon program. Verify contractor certification through nrpp.info or nrsb.org before engaging any radon professional.

Radon Disclosure Requirements in Indiana

Indiana’s real estate disclosure form requires sellers to disclose known conditions that materially affect the property, including environmental hazards. While Indiana does not have a radon-specific disclosure statute, the general material defect disclosure requirement covers known elevated radon conditions. Indiana real estate contracts routinely include radon contingencies. The Indiana Association of Realtors provides guidance to agents on radon disclosure best practices. Sellers with known elevated radon levels should disclose and document this information.

Radon-Resistant New Construction (RRNC) in Indiana

Indiana does not have a statewide RRNC mandate for new residential construction. The Indiana Residential Code does not require RRNC features as a standard provision statewide. EPA and ISDH recommend RRNC for new construction in Zone 1 northern Indiana counties. The IRC Appendix F provisions may be adopted locally. Buyers of new construction in Indiana should ask their builder about RRNC inclusion, particularly in northern Zone 1 counties.

Highest-Radon Counties and Areas in Indiana

Indiana’s highest-radon areas are concentrated in the northern glaciated counties. Lake, LaPorte, Porter, St. Joseph, Elkhart, and Kosciusko counties in northwestern and north-central Indiana have shown elevated average radon levels in state surveys. The Indianapolis metropolitan area (Marion, Hamilton, Hendricks, Johnson, Hancock counties) shows moderate to high radon levels. Southern Indiana counties generally have lower but still meaningful radon potential.

Testing Resources for Indiana Residents

The Indiana State 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 Indiana homes have elevated radon?

Approximately 35–40% of Indiana homes are estimated to have radon levels above 4.0 pCi/L. Northern Indiana counties with glacial geology tend to show the highest readings.

Does Indiana require radon contractor certification?

Indiana requires NRPP or NRSB national certification for radon professionals. There is no separate Indiana-specific licensing statute — national certification is the operative credential. Verify at nrpp.info or nrsb.org before hiring.

Does Indiana require RRNC for new construction?

No statewide mandate. EPA recommends RRNC for new construction in Zone 1 northern Indiana counties. Ask your builder directly about RRNC inclusion before signing a new construction contract.

Colorado has some of the highest radon levels in the western United States, with an estimated average indoor radon level around 6.2 pCi/L — well above the EPA action level of 4.0 pCi/L. The Colorado Department of Public Health and Environment estimates that approximately 50% of Colorado homes have elevated radon. Colorado’s geology — including uranium-rich geological formations in the Front Range, granitic bedrock, and shale — creates high radon potential across much of the state, including the heavily populated Denver metro corridor.

EPA Radon Zone Designation

Colorado is predominantly EPA Radon Zone 1. Most Front Range and mountain Colorado counties are Zone 1. The highest-risk areas include counties along the Front Range corridor (El Paso, Jefferson, Arapahoe, Adams, Boulder, Larimer counties) and the western slope counties overlying uranium-bearing geology. Eastern plains counties are generally Zone 2 to Zone 3.

Radon Contractor Licensing in Colorado

Colorado requires radon contractors to hold current NRPP or NRSB certification to perform radon measurement and mitigation work. The Colorado Department of Public Health and Environment’s radon program maintains a list of certified radon professionals. Colorado does not have a separate state radon contractor licensing statute independent of national certification — NRPP or NRSB certification is the operative requirement. Verify contractor certification at nrpp.info or nrsb.org before hiring.

Radon Disclosure Requirements in Colorado

Colorado does not have a radon-specific disclosure statute for residential real estate transactions. However, Colorado’s general real estate disclosure law requires sellers to disclose known material adverse facts — and known elevated radon test results almost certainly qualify as a material fact under this standard. Real estate contracts in Colorado routinely include radon contingencies, and radon testing during the inspection period is standard practice in the Front Range metro area. The Colorado Real Estate Commission’s disclosure form does not include a specific radon question, but agents and sellers have a common law duty to disclose known adverse conditions.

Radon-Resistant New Construction (RRNC) in Colorado

Colorado has enacted RRNC requirements for new residential construction in high-radon areas. Some Colorado municipalities — particularly in El Paso County (Colorado Springs) and the Denver metro — require RRNC features for new construction. The IRC Appendix F provisions have been adopted in various Colorado jurisdictions. The CDPHE strongly recommends RRNC for all new construction in Colorado’s Zone 1 areas. Buyers of new Colorado construction should confirm with the builder and local building department whether RRNC is required and what specific provisions apply.

Highest-Radon Counties and Areas in Colorado

Colorado’s highest-radon areas include Front Range counties: El Paso (Colorado Springs area), Jefferson (Denver west suburbs), Arapahoe, Adams, Boulder, and Larimer counties. Mountain counties including Eagle, Summit, Park, and Teller also show elevated radon. Western slope counties overlying uranium-bearing geology in the Grand Junction area (Mesa County) have historically high readings. The CDPHE maintains county-level radon data on their website.

Testing Resources for Colorado Residents

The Colorado Department of Public Health and Environment 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

Is Colorado a high-radon state?

Yes. Colorado has one of the highest average indoor radon levels in the western U.S., estimated at 6.2 pCi/L statewide. Approximately 50% of Colorado homes test above the EPA action level. Radon is a significant public health concern across Colorado’s Front Range and mountain communities.

Does Colorado require radon disclosure in real estate?

Colorado has no radon-specific disclosure statute, but sellers have a common law duty to disclose known material adverse facts — including known elevated radon levels. Radon contingencies and testing are standard in Colorado real estate transactions.

What counties in Colorado have the highest radon?

El Paso, Jefferson, Arapahoe, Adams, Boulder, and Larimer counties along the Front Range have high average radon levels. Mountain counties including Eagle, Summit, Park, and Teller also show elevated readings. Western slope counties near Grand Junction have historically high concentrations.

Minnesota has consistently high radon levels, with the Minnesota Department of Health estimating that approximately 2 in 5 Minnesota homes (40%) have radon levels above 4.0 pCi/L. Minnesota’s geology — including granitic bedrock, glacial outwash, and uranium-bearing formations — produces elevated radon potential across much of the state. The Minnesota Radon Awareness Act, enacted in 2014, established specific disclosure and awareness requirements.

EPA Radon Zone Designation

Minnesota is predominantly EPA Radon Zone 1. Most Minnesota counties are Zone 1. The highest-radon areas are concentrated in the Iron Range of northeastern Minnesota (where uranium-bearing rock is prevalent), the granite regions of central Minnesota, and the glaciated plains of western Minnesota. The Twin Cities metropolitan area has significant radon risk, particularly in older housing stock.

Radon Contractor Licensing in Minnesota

Minnesota requires radon contractors to hold current NRPP or NRSB certification AND a Minnesota-specific radon contractor license issued by the Minnesota Department of Health. Minnesota’s radon contractor licensing program is among the more comprehensive in the Midwest. Licensed contractors must pass examinations, carry insurance, and complete continuing education. The MDH maintains a searchable database of licensed radon contractors. Since 2014, hiring an unlicensed radon contractor in Minnesota is a violation of the Minnesota Radon Awareness Act.

Radon Disclosure Requirements in Minnesota

The Minnesota Radon Awareness Act (Minnesota Statutes Chapter 144.4961) enacted in 2014 established specific radon disclosure requirements for real estate transactions. Key provisions: sellers must disclose to buyers whether the home has been tested for radon and provide any test results; sellers must provide the Minnesota Department of Health radon disclosure form; any mitigation system must be disclosed. Minnesota also requires that the EPA radon pamphlet or equivalent MDH materials be provided to buyers. These requirements apply to single-family homes and condominiums.

Radon-Resistant New Construction (RRNC) in Minnesota

Minnesota does not have a statewide mandate requiring RRNC for all new construction, but the MDH strongly recommends RRNC. Some Minnesota municipalities — particularly in the Twin Cities metro area — have incorporated RRNC requirements locally. Minnesota’s building code includes provisions that enable RRNC adoption. Given Minnesota’s high radon prevalence, the MDH recommends all new residential construction in Zone 1 areas include RRNC features per AARST-ANSI RRNC-2022.

Highest-Radon Counties and Areas in Minnesota

Minnesota’s highest-radon areas include the Iron Range counties of northeastern Minnesota (St. Louis, Lake, Cook counties), granite bedrock areas in central Minnesota (Morrison, Todd, Otter Tail counties), and western Minnesota counties in the glaciated plains. The Minneapolis-Saint Paul metropolitan area spans multiple high-radon counties including Hennepin, Ramsey, Anoka, Dakota, Washington, and Scott. The MDH publishes county-level radon data based on testing results reported to the state.

Testing Resources for Minnesota Residents

The Minnesota 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

Does Minnesota have a radon disclosure law?

Yes. The Minnesota Radon Awareness Act (2014) requires sellers to disclose known radon test results and provide MDH radon disclosure materials to buyers in real estate transactions. Mitigation systems must also be disclosed.

Does Minnesota require radon contractor licensing?

Yes. Minnesota requires both NRPP or NRSB national certification AND a Minnesota-specific radon contractor license. Verify license status through the Minnesota Department of Health before hiring any contractor.

What is the radon level in Minnesota homes?

The Minnesota Department of Health estimates approximately 40% of Minnesota homes — roughly 2 in 5 — have radon levels above 4.0 pCi/L. Minnesota’s average is among the highest in the nation, making testing essential for all Minnesota homes.

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.