Category: Radon Mitigation

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.

Pennsylvania consistently ranks among the highest-radon states in the U.S., with an estimated average indoor radon level around 6.0 pCi/L statewide. The Pennsylvania Department of Environmental Protection estimates that approximately 40% of Pennsylvania homes have radon levels above the EPA action level. Pennsylvania’s geology — including Reading Prong granite, black shale, and carbonate rock formations — creates particularly high radon potential in the southeastern and south-central regions of the state.

EPA Radon Zone Designation

Pennsylvania is predominantly EPA Radon Zone 1. The majority of Pennsylvania counties are Zone 1, with particularly high radon potential in counties overlying the Reading Prong geological formation in the southeast (Bucks, Chester, Montgomery, Berks, Lehigh, Northampton counties) and limestone/carbonate geology in the south-central region (Adams, Cumberland, Franklin, York, Lancaster counties). Some northern and western counties are Zone 2.

Radon Contractor Licensing in Pennsylvania

Pennsylvania has a comprehensive radon contractor licensing program administered by the Pennsylvania Department of Environmental Protection. Radon measurement and mitigation contractors must hold a Pennsylvania state license to legally perform radon services in the state. Pennsylvania licensing requires passing state examinations (or demonstrating NRPP/NRSB certification), carrying liability insurance, and completing continuing education. The DEP maintains an online searchable database of licensed radon professionals at dep.pa.gov. Performing radon work without a Pennsylvania license is illegal and a violation of the Radon Certification Act.

Radon Disclosure Requirements in Pennsylvania

Pennsylvania has specific radon disclosure requirements under its real estate disclosure law. Sellers must complete the Seller’s Property Disclosure Statement, which includes questions about radon — specifically whether the property has been tested and what the results were, and whether a radon mitigation system is present. Pennsylvania does not require sellers to test before selling, but known results must be disclosed. Given Pennsylvania’s high radon prevalence, radon contingencies are standard in Pennsylvania real estate transactions, and buyers routinely request independent testing.

Radon-Resistant New Construction (RRNC) in Pennsylvania

Pennsylvania does not have a statewide mandate requiring RRNC for all new construction, but the Pennsylvania DEP strongly recommends RRNC for new homes — particularly in Zone 1 counties. Some municipalities within Pennsylvania have adopted local RRNC requirements. The IRC Appendix F RRNC provisions are available for local adoption. Buyers of new construction in Pennsylvania should ask their builder directly whether RRNC features are included, particularly in the high-radon southeastern and south-central counties.

Highest-Radon Counties and Areas in Pennsylvania

Pennsylvania’s highest-radon areas include counties overlying the Reading Prong geological formation: Bucks, Chester, Montgomery, Berks, Lehigh, and Northampton in the southeast. South-central counties including Adams, York, Lancaster, Cumberland, and Franklin — which overlie limestone and carbonate geology — also show high average radon levels. The PA DEP’s county-level radon data is available on their website and shows average indoor radon measurements for each county based on test results submitted to the program.

Testing Resources for Pennsylvania Residents

The Pennsylvania Department of Environmental Protection 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 Pennsylvania require radon contractor licensing?

Yes. Pennsylvania has a comprehensive Radon Certification Act requiring contractors to hold a state license for radon measurement and mitigation work. Verify license status through the Pennsylvania DEP radon program before hiring any contractor.

What parts of Pennsylvania have the highest radon levels?

The Reading Prong geological formation in southeastern Pennsylvania (Bucks, Chester, Montgomery, Berks, Lehigh, Northampton counties) has some of the nation’s highest radon concentrations. South-central counties including Adams, York, Lancaster, Cumberland, and Franklin also show elevated average radon levels.

Is radon testing required when buying a house in Pennsylvania?

Not legally required, but strongly recommended and standard practice. Pennsylvania sellers must disclose known radon test results, but they are not required to test before selling. Buyers should always conduct independent testing during the inspection contingency period.

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Related Radon Resources

• EPA Radon Zone Map: What Zone 1, 2, and 3 Mean
• NRPP and NRSB Radon Contractor Certification Explained
• Radon Disclosure Laws: What Sellers Must Tell Buyers
• How to Find and Hire a Good Radon Contractor

Iowa has the highest average indoor radon levels of any U.S. state. The Iowa Department of Public Health estimates that approximately 71% of Iowa homes test above the EPA action level of 4.0 pCi/L, and Iowa’s statewide average indoor radon level of roughly 8.5 pCi/L is the highest in the nation. Every county in Iowa is designated EPA Radon Zone 1.

EPA Radon Zone Designation

Iowa is predominantly EPA Radon Zone 1. All 99 Iowa counties are Zone 1 — the highest radon potential designation — reflecting the state’s geology of uranium-rich glacial deposits, black shale, and granite-derived soils across the entire state.

Radon Contractor Licensing in Iowa

Iowa requires radon contractors to hold certification from NRPP or NRSB to legally conduct radon measurement and mitigation work. Iowa’s radon program enforces contractor certification requirements and maintains a list of certified professionals. Performing radon mitigation without certification in Iowa may violate state public health regulations. Verify any contractor’s current certification status through the Iowa Department of Public Health radon program website before hiring.

Radon Disclosure Requirements in Iowa

Iowa requires sellers of real property to disclose known radon test results. The Iowa disclosure requirement applies to residential real estate transactions and directs sellers to disclose whether the property has been tested for radon and the results of any such test. Iowa also requires that buyers be provided information about radon and its health risks. Given that 71% of Iowa homes exceed the EPA action level, radon contingencies and testing are standard practice in Iowa real estate transactions.

Radon-Resistant New Construction (RRNC) in Iowa

Iowa mandates radon-resistant new construction features for new residential construction. As a Zone 1 state with the nation’s highest average radon levels, Iowa’s building code requirements include RRNC provisions for new homes. Builders constructing new homes in Iowa should confirm current RRNC requirements with their local building department, as specific requirements have evolved and local adoption varies. EPA strongly recommends full RRNC per AARST-ANSI RRNC-2022 for all new Iowa construction.

Highest-Radon Counties and Areas in Iowa

All 99 Iowa counties are Zone 1. The counties with historically highest average radon measurements include Linn, Polk, Johnson, Scott, and Black Hawk — the state’s most populous counties — as well as the geological formation areas in north-central and northeastern Iowa where glacial deposits are thickest. Iowa State University Extension and IDPH have documented elevated radon across the entire state, with rural counties in northern Iowa showing some of the highest averages.

Testing Resources for Iowa Residents

The Iowa Department of Public 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

Is Iowa a high-radon state?

Iowa is the highest-radon state in the U.S. by average indoor concentration. Approximately 71% of Iowa homes test above the EPA action level of 4.0 pCi/L, and Iowa’s statewide average of roughly 8.5 pCi/L exceeds all other states. Testing is essential for every Iowa home.

Are radon contractors required to be licensed in Iowa?

Yes. Iowa requires radon measurement and mitigation contractors to hold current NRPP or NRSB certification. Verify contractor credentials through the Iowa Department of Public Health radon program before hiring.

Does Iowa require radon disclosure when selling a home?

Yes. Iowa sellers must disclose known radon test results to buyers. Given that the majority of Iowa homes exceed the EPA action level, radon testing and disclosure are standard components of Iowa real estate transactions.

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Related Radon Resources

• EPA Radon Zone Map: What Zone 1, 2, and 3 Mean
• NRPP and NRSB Radon Contractor Certification Explained
• Radon Disclosure Laws: What Sellers Must Tell Buyers
• Radon-Resistant New Construction: Building Codes Explained

The most cost-effective moment to address radon is during new home construction — before the slab is poured, before walls are framed, before any remediation is necessary. Building codes are the mechanism through which governments mandate this timing advantage, requiring builders to incorporate radon-resistant features into new residential construction. But because the U.S. building code system is decentralized, RRNC requirements vary dramatically by state and locality.

The International Residential Code and Radon

The International Residential Code (IRC) is a model building code developed by the International Code Council (ICC) and adopted — in some form — by most U.S. states. The IRC includes an appendix (Appendix F: Radon Control Methods) that specifies RRNC requirements for new residential construction. Key IRC Appendix F requirements align with EPA guidance and AARST-ANSI RRNC-2022:

• 4-inch thick gas-permeable layer (3/4″ gravel or equivalent) under the slab
• Polyethylene vapor barrier (minimum 6-mil) between the gas-permeable layer and the slab
• 3-inch or 4-inch PVC vent pipe routed from the sub-slab to above the roofline
• Electrical junction box or outlet in the attic at the anticipated fan location
• Sealing of all major slab penetrations and joints

The critical limitation: IRC appendices are optional. Jurisdictions that adopt the IRC base code are not automatically required to adopt Appendix F. A state can adopt the full IRC with Appendix F (making RRNC mandatory), adopt the IRC without Appendix F (making RRNC voluntary), or adopt a modified version with different RRNC requirements.

Where RRNC Is Mandatory

As of 2026, the following categories of jurisdictions require RRNC:

States with Statewide RRNC Mandates

Several high-radon-risk states have enacted statewide RRNC requirements for new residential construction in Zone 1 (or sometimes all) counties. States with statewide or zone-specific RRNC mandates include portions of Colorado, Iowa, Maryland, Minnesota, Montana, North Dakota, South Dakota, and others. Requirements vary in scope — some mandate full RRNC for all new single-family construction, others require it only in Zone 1 counties or for structures with ground-contact foundations.

Municipalities with Local RRNC Requirements

In states without statewide RRNC mandates, individual counties and municipalities may have adopted RRNC requirements locally. This is common in Zone 1 counties where local officials have responded to elevated community radon levels even in the absence of state mandate. Local adoption varies and is not comprehensively tracked — contact your local building department to confirm requirements for a specific project location.

HUD-Assisted New Construction

Federally assisted new construction projects in EPA Zone 1 counties are subject to HUD radon requirements, which include RRNC features for multifamily projects. This is a federal requirement that operates independently of state or local building codes.

Where RRNC Is Strongly Recommended but Not Required

In the majority of U.S. jurisdictions, RRNC is EPA-recommended but not legally required. Builders in these areas can include RRNC features voluntarily. EPA recommends RRNC for all new construction in Zone 1 counties regardless of local mandate, and recommends it for Zone 2 and Zone 3 as well given the low incremental cost during construction.

Buyers of new construction in non-mandating jurisdictions should ask their builder directly:

• “Does this home include RRNC features per IRC Appendix F or AARST-ANSI RRNC-2022?”
• “Is a passive radon vent pipe included in the construction plans?”
• “Is there a dedicated electrical outlet in the attic for a future radon fan?”

If the builder does not include RRNC, request it as a contract upgrade. The incremental cost is typically $350–$700 — a fraction of post-construction mitigation ($800–$2,500+) and a fraction of the home’s overall purchase price.

The AARST-ANSI RRNC-2022 Standard

Where IRC Appendix F provides the building code mechanism, AARST-ANSI RRNC-2022 provides the comprehensive technical specification. RRNC-2022 is more detailed than the IRC appendix on several points:

• Specifications for alternative gas-permeable materials where gravel is impractical
• Detailed sealing requirements for vapor barrier seams, penetrations, and wall interfaces
• Crawl space-specific RRNC provisions (vented vs. encapsulated designs)
• Quality verification requirements during construction
• Labeling requirements for passive RRNC installations
• Provisions for manufactured home foundations

Projects referencing AARST-ANSI RRNC-2022 in their specifications are held to a higher technical standard than IRC Appendix F alone. Some state radon programs have updated their RRNC requirements to reference RRNC-2022 rather than older EPA guidance documents.

Frequently Asked Questions

Is my new home required to have radon-resistant features?

It depends entirely on your state and local jurisdiction. In states with statewide RRNC mandates, yes — new construction must include IRC Appendix F or AARST-ANSI RRNC features. In most U.S. jurisdictions, RRNC is EPA-recommended but not legally required. Ask your builder directly whether RRNC is included, and request it if it is not — the upgrade cost during construction is minimal.

What is the difference between IRC Appendix F and AARST-ANSI RRNC-2022?

IRC Appendix F is the building code mechanism — the legal framework through which jurisdictions mandate RRNC in new construction. AARST-ANSI RRNC-2022 is the technical standard — the detailed specification for how RRNC components should be installed. Both address the same system components (gas-permeable layer, vapor barrier, vent pipe, electrical outlet), but RRNC-2022 is more comprehensive and is the current authoritative technical reference.

My new home has a passive radon pipe — do I need to do anything?

Test for radon after at least 60 days of occupancy. If results are at or above 4.0 pCi/L, activate the system by adding a fan to the existing pipe — a 1–2 hour installation costing $200–$500. If results are below 4.0 pCi/L, retest every 2 years. The passive pipe is infrastructure for future activation; it does not guarantee low radon levels without a fan.

Radon disclosure in real estate is not governed by a single federal law. Instead, a patchwork of state statutes, administrative rules, and general real estate disclosure obligations creates a varied landscape in which seller requirements differ dramatically by state. In some states, sellers must proactively disclose any known radon test result above a threshold. In others, radon disclosure falls under the general duty to disclose material defects — and sellers who know about elevated radon and say nothing may face post-closing liability even without a specific radon statute.

No Federal Radon Disclosure Law for Residential Sales

Federal law does not mandate radon disclosure for the sale of private residential property. The Indoor Radon Abatement Act of 1988 directed EPA to develop guidance but created no seller disclosure obligation. The Real Estate Settlement Procedures Act (RESPA) and Truth in Lending Act (TILA) govern financial disclosures in real estate transactions but do not address radon. The only federal radon disclosure requirement applies to HUD-assisted housing, where tenants and buyers must be notified of known radon hazards.

Three Types of State Radon Disclosure Frameworks

Type 1: Specific Radon Disclosure Statute

Some states have enacted radon-specific disclosure statutes that explicitly require sellers to disclose radon-related information. Requirements vary by state but may include:

• Disclosure of any known radon test result (regardless of level)
• Disclosure of any known radon test result at or above the EPA action level
• Disclosure of the presence of a radon mitigation system
• Provision of the EPA “Home Buyer’s and Seller’s Guide to Radon” pamphlet
• Disclosure of whether any test has ever been conducted in the home

States with explicit radon disclosure statutes or regulations include (as of 2026): Florida, Illinois, Maine, Virginia, and others. Statute specifics change — verify current requirements with your state real estate commission or a licensed real estate attorney.

Type 2: General Material Defect Disclosure

Nearly all states require sellers to disclose known material defects in the property — conditions that would affect the property’s value or a buyer’s decision to purchase. In states without a radon-specific disclosure law, elevated radon can still constitute a known material defect that must be disclosed under the general duty.

The key word is “known.” A seller who has never tested does not have a disclosure obligation they are not aware of. A seller who tested five years ago, found 12 pCi/L, and never mitigated or disclosed — that is a different legal situation in most states, regardless of whether a radon-specific law exists. Courts in multiple states have found liability under general misrepresentation or fraud theories when sellers concealed known radon test results even without state radon disclosure statutes.

Type 3: No Specific Requirement (Buyer Beware)

A smaller number of states have neither a specific radon disclosure statute nor a general material defect disclosure requirement robust enough to clearly cover radon. In these states, the buyer’s primary protection is their own due diligence — testing during the inspection contingency period. Buyers in these states should always include a radon contingency in their purchase offer and conduct independent testing.

What Sellers Should Disclose (Best Practice, All States)

Regardless of state-specific requirements, the following disclosure approach protects sellers from post-closing liability and reflects ethical practice:

• Disclose all known radon test results — not just recent ones and not just elevated ones
• Disclose the presence of any radon mitigation system, including the type, installation date, and contractor
• Disclose whether the home has ever been tested and what the results were
• Provide copies of all test reports and post-mitigation testing documentation
• Do not selectively disclose only favorable results while omitting unfavorable historical tests

Sellers who test before listing — and mitigate if needed — have the most straightforward disclosure position: known test results, documented mitigation, confirmed post-mitigation levels. The paper trail protects against post-closing claims.

What Buyers Should Know

• Include a radon contingency in your offer: Specifies the test protocol, the threshold (typically 4.0 pCi/L), and the remedies available to you if the threshold is exceeded
• Conduct independent testing: Do not rely on seller-provided test results as your only verification — even in states where sellers are required to disclose, the seller’s test may be old, improperly conducted, or selectively presented
• Request all historical test results: Ask specifically for all test results ever conducted — not just the most recent one
• Verify any existing mitigation system: Request contractor documentation, post-mitigation test results, and check that the U-tube manometer shows the system is operating

Frequently Asked Questions

Am I required to disclose radon when selling my house?

It depends on your state. States with radon-specific disclosure statutes require disclosure of known results; most other states require disclosure of known material defects that would affect a buyer’s decision — which elevated radon likely qualifies as. Consult a real estate attorney in your state for specific obligations. As a practical matter, failing to disclose known elevated radon exposes sellers to post-closing litigation risk in most jurisdictions even where no specific statute exists.

Do I have to disclose old radon test results?

Yes, if you are aware of them. “Known material defect” disclosure obligations apply to all known information — not just recent or convenient information. A radon test result from 10 years ago showing 15 pCi/L, followed by no mitigation or retesting, is a known condition that almost certainly triggers disclosure obligations under either specific radon statutes or general defect disclosure requirements.

What if the seller did not disclose a known radon problem?

If a seller knew about elevated radon and failed to disclose it in a state with a disclosure obligation (either radon-specific or general material defect), the buyer may have grounds for post-closing claims including fraud, misrepresentation, or breach of contract. Remedies vary by state but may include cost of mitigation, diminution in property value, or in egregious cases, rescission of the transaction. Consult a real estate attorney in your state with the specific facts of the situation.

Not all radon contractors are equally regulated. In some states, performing radon mitigation or measurement requires a state license — examination, insurance, continuing education, and annual renewal. In others, there is no requirement at all: anyone can install a radon system or conduct a radon test legally, regardless of training or competence. Knowing which type of state you live in is the first step toward protecting yourself when hiring.

The Spectrum of State Radon Contractor Regulation

State radon contractor requirements fall into several categories:

States with Comprehensive State Licensing Programs

These states have enacted radon-specific licensing statutes requiring contractors to obtain a state license to legally perform radon work. Licensing typically requires:

• Passing a state examination or completing state-approved training
• Demonstrating NRPP or NRSB national certification (some states accept national certification in lieu of a separate state exam)
• Carrying general liability insurance and in some states E&O (errors and omissions) insurance
• Paying a licensing fee and renewing annually or biennially
• Completing continuing education during each license period

States with comprehensive licensing programs (as of 2026) include: Florida, Illinois, Iowa, Kansas, Maine, Maryland, Minnesota, Montana, New Jersey, New York, Ohio, Pennsylvania, Tennessee, and others. Requirements change — verify current status with your state radon program.

States That Accept National Certification as Licensing

Some states do not have separate state licensing requirements but have enacted laws or regulations that require contractors to hold current NRPP or NRSB certification to perform radon work legally. The practical effect is similar to licensing — the national certification serves as the state qualification. States in this category include several that require certification for at least some types of radon work (real estate measurement, school testing, or mitigation work with homeowner contracts).

States with No Radon Contractor Regulation

Roughly half of U.S. states have no radon-specific contractor licensing or certification requirements. In these states, there is no legal barrier to anyone performing radon work — from installation of mitigation systems to conducting real estate radon tests — regardless of training or competence. This does not mean good contractors do not exist in these states; many voluntarily maintain NRPP or NRSB certification. But it means you cannot rely on legal licensing as a screening tool — you must verify credentials directly.

Measurement vs. Mitigation Licensing: Different Requirements

Many states regulate measurement and mitigation separately. A contractor may be licensed for one but not the other:

• Measurement-only licensing: Required for conducting certified radon tests (particularly for real estate), even in states where mitigation has no licensing requirement
• Mitigation-only licensing: Required for installing systems; the contractor may not be authorized to conduct certified post-mitigation measurements
• Dual certification/licensing: Some professionals hold both; many do not — confirm which credential a professional holds before engaging them for a specific service

How to Verify a Contractor’s State License

• Your state health department radon program: The most authoritative source. State radon programs maintain lists of currently licensed contractors and often have an online lookup tool. Search for “[your state] radon program” or “[your state] radon contractor license”.
• NRPP directory: nrpp.info — searchable by name, zip code, or certification number. Shows current certification status and discipline (measurement, mitigation, or both).
• NRSB directory: nrsb.org — same search capability for NRSB-certified professionals.
• Ask directly: Request the contractor’s state license number and national certification number. Ask which certification they hold (measurement, mitigation, or both). A legitimate professional provides this immediately.

What “No State Licensing Requirement” Means in Practice

In states without radon contractor regulation, your protection comes from:

• Voluntarily certified contractors: NRPP and NRSB directories include contractors in unregulated states who have chosen to obtain and maintain national certification. Prioritize these contractors.
• Contract terms: A written contract specifying that installation will follow AARST-ANSI SGM-SF requirements creates an enforceable standard even where licensing does not.
• Workmanship warranty: Reputable contractors in unregulated states typically offer warranties equivalent to those required in licensed states. Get the warranty in writing before work begins.
• Post-mitigation independent testing: Regardless of contractor certification status, placing your own post-mitigation test device independently confirms whether the system is achieving its purpose.

Frequently Asked Questions

Does my state require a licensed radon contractor?

Approximately half of U.S. states require some form of radon contractor licensing or certification. The fastest way to find your state’s specific requirements is to search “[your state] radon program” through your state health or environment department website. Many state radon programs maintain a list of licensed contractors and post current requirements online. Requirements change — information that is two or more years old may be outdated.

Can an unlicensed contractor install a radon system?

In states without radon contractor licensing requirements, yes — legally. In states with licensing requirements, performing radon mitigation without a license is illegal and may void warranty coverage, create liability for the homeowner (if work requires a building permit), and result in a system that does not meet AARST-ANSI standards. Always verify your state’s requirements and the contractor’s credentials before engaging anyone for radon work.

Does a radon contractor need to be licensed to test and mitigate?

Often yes for both activities — but through separate credentials. In most states with licensing, measurement (testing) and mitigation (system installation) are separately licensed or certified. A contractor licensed only for mitigation may not be authorized to conduct the certified post-mitigation measurement. Verify both credentials when a single contractor proposes to both install and certify the post-installation result.

When a radon professional says they follow “AARST standards,” they are referring to a specific set of American National Standards developed by the American Association of Radon Scientists and Technologists (AARST) and approved by the American National Standards Institute (ANSI). These standards are the technical backbone of professional radon practice in the United States — governing how systems are installed, how measurements are conducted, and what constitutes acceptable post-mitigation performance. Understanding what these standards require helps you evaluate whether a contractor is following best practice or cutting corners.

What Is AARST?

The American Association of Radon Scientists and Technologists (AARST) is the primary professional organization for radon professionals in the United States. Founded in 1988 — the same year as the Indoor Radon Abatement Act — AARST administers the National Radon Proficiency Program (NRPP), develops technical standards through a consensus process, and advocates for radon-related policy. AARST’s standards are developed collaboratively by measurement professionals, mitigators, researchers, regulators, and public health specialists.

What Is ANSI Approval?

The American National Standards Institute (ANSI) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, and systems in the United States. ANSI accreditation ensures that standards are developed through a documented, consensus-based process with balanced stakeholder representation and opportunities for public comment. AARST’s key radon standards are ANSI-approved, meaning they carry the authority of the U.S. voluntary consensus standards system — the same system that produces ASTM, ASHRAE, and ASME standards used throughout U.S. construction and engineering.

The Core AARST-ANSI Radon Standards

ANSI/AARST SGM-SF: Mitigation Standard for Single-Family Homes

Standard of Practice for Mitigation of Radon in Schools and Large Buildings — Single-Family (SGM-SF) is the governing standard for radon mitigation system design and installation in single-family residential buildings. This is the standard that determines:

• Required pre-installation diagnostic testing procedures
• Fan placement requirements (unconditioned space only)
• Pipe sizing, routing, and joint cementing requirements
• Slab sealing requirements
• System performance indicator (manometer) requirements
• Required labeling on installed systems
• Post-installation testing timing and protocol
• Documentation requirements for installed systems

SGM-SF is referenced in NRPP certification requirements and is the standard against which certified Radon Mitigation Specialists are tested. Many state radon programs and contractor licensing requirements specifically cite SGM-SF compliance as a requirement for licensed work.

ANSI/AARST RMS-LB: Mitigation Standard for Large Buildings

The Radon Mitigation Standard for Large Buildings (RMS-LB) covers radon mitigation in schools, commercial buildings, multifamily housing, and other large structures. It addresses the additional complexity of large-building mitigation: multiple foundation zones, complex HVAC integration, sub-membrane depressurization for large crawl spaces, and the heightened documentation and verification requirements appropriate for public-use buildings.

ANSI/AARST MAMF: Measurement Standard for Multi-Family and Large Buildings

The Measurement and Mitigation Protocol for Large Buildings (MAMF) governs radon measurement in commercial and multifamily residential settings. For real estate professionals, the most relevant application is its guidance on certified measurement for real estate transactions — particularly in multifamily and commercial properties where residential measurement standards (which address single-family protocol) may not directly apply.

ANSI/AARST RRNC-2022: Radon-Resistant New Construction Standard

The Radon-Resistant New Construction standard (RRNC-2022) defines the technical requirements for incorporating radon-resistant features into new residential construction. It is the most current and comprehensive technical document governing RRNC — superseding earlier EPA guidance documents on the topic. Key content includes:

• Gas-permeable layer specifications (aggregate type, depth, coverage)
• Vapor barrier specifications (minimum thickness, seam overlap, sealing requirements)
• Vent pipe specifications (diameter, schedule, routing, termination)
• Electrical outlet requirements for future fan activation
• Crawl space-specific RRNC provisions
• Quality verification requirements

ANSI/AARST Series SSDS: Soil Suction Depressurization Standards

The SSDS series covers specific mitigation methods including sub-slab depressurization, sub-membrane depressurization, drain-tile depressurization, and block-wall depressurization — providing technical specifications for each method type that exceed the general requirements in SGM-SF.

How Standards Are Used in Practice

AARST-ANSI standards function as the technical reference layer for radon professional practice in several ways:

• Certification examinations: NRPP and NRSB certification exams test knowledge of AARST-ANSI standards — a certified professional is expected to know and follow these requirements
• State licensing requirements: States with radon contractor licensing often cite AARST-ANSI standards as the technical basis for licensed work — contractors must demonstrate compliance
• Workmanship warranty basis: When a mitigator’s workmanship warranty specifies what they will and will not do on a callback, the underlying technical obligation is typically SGM-SF compliance
• Litigation reference: In disputes about radon mitigation quality or post-mitigation testing results, AARST-ANSI standards provide the objective technical benchmark against which contractor work is evaluated
• Real estate due diligence: Buyers and home inspectors can reference AARST-ANSI standards to evaluate whether an existing mitigation system was installed to professional standards

Frequently Asked Questions

Are AARST-ANSI radon standards legally binding?

AARST-ANSI standards are voluntary consensus standards — they are not automatically law. However, they become legally operative when incorporated by reference into state licensing requirements, building codes, or contract specifications. When a state radon licensing law requires compliance with SGM-SF, that standard becomes legally binding in that state. When a contractor’s contract specifies AARST-ANSI standard compliance, violation becomes a breach of contract. Courts also routinely treat industry consensus standards as evidence of the duty of care applicable to professionals in negligence cases.

How do I know if my mitigation contractor followed AARST standards?

Key SGM-SF compliance indicators to check: fan is in unconditioned space (attic, exterior, or garage — not a finished basement or utility room); all PVC joints are cemented (not dry-fitted); a U-tube manometer is installed and visible; required warning label is on the pipe; slab core hole is sealed with hydraulic cement (not just foam); and the contractor provided written documentation of pre-mitigation radon level, system specifications, and post-mitigation test results. A system missing any of these elements is likely not fully SGM-SF compliant.

Where can I get copies of AARST-ANSI radon standards?

AARST-ANSI standards are available for purchase through the AARST website (aarst.org) and through the ANSI standards store (ansi.org). Some standards are available for free download from AARST as part of their public education mission. State radon programs sometimes make the most relevant standard (typically SGM-SF) available as a reference document.

EPA’s Map of Radon Zones divides every U.S. county into one of three zones based on predicted average indoor radon levels. The map is widely cited in radon regulations, building codes, and HUD requirements — but it is frequently misunderstood. Zone designation does not tell you your home’s radon level. It tells you the predicted average for your county, which may have little bearing on the specific geology beneath your foundation.

The Three Radon Zones

Zone 1: Highest Potential (Predicted Average Above 4.0 pCi/L)

Zone 1 counties have the highest predicted indoor radon potential. EPA’s methodology predicts that the average indoor radon level in Zone 1 counties exceeds the EPA action level of 4.0 pCi/L. Zone 1 counties are concentrated in the Northern Plains, Rocky Mountain states, Pennsylvania, Ohio, Iowa, and parts of the mid-Atlantic — regions with uranium-rich geology including granite formations, black shale, and glacial deposits.

Zone 1 status triggers several regulatory consequences:

• HUD requires radon testing for federally assisted multifamily housing in Zone 1 counties
• Some states mandate RRNC (Radon-Resistant New Construction) for residential construction in Zone 1 counties
• EPA recommends RRNC for all new construction in Zone 1 regardless of state requirements
• Some states with school radon testing mandates prioritize Zone 1 districts

Zone 2: Moderate Potential (Predicted Average 2.0–4.0 pCi/L)

Zone 2 counties have predicted average indoor radon levels between the EPA “consider mitigating” level (2.0 pCi/L) and the action level (4.0 pCi/L). Zone 2 represents a substantial portion of U.S. counties. EPA still recommends testing in Zone 2 and recommends RRNC for new construction — the lower priority relative to Zone 1 reflects statistical averages, not safety.

Zone 3: Lowest Potential (Predicted Average Below 2.0 pCi/L)

Zone 3 counties have the lowest predicted radon potential. The average predicted indoor level is below 2.0 pCi/L. EPA still recommends testing in Zone 3 — individual homes in Zone 3 counties can and do have elevated radon due to local geology, soil conditions, and construction variations. “Low-radon zone” does not mean “radon-free zone.”

How the Zone Map Was Developed

EPA published the original Radon Zone Map in 1993 based on data from three sources:

• Indoor radon surveys: State radon measurement data from the EPA/State Residential Radon Survey conducted in the late 1980s, providing actual indoor radon measurements from thousands of homes across the country
• Aerial radiometric surveys: U.S. Geological Survey (USGS) airborne gamma-ray data measuring surface uranium, thorium, and potassium concentrations — proxies for radon-producing geology
• Geology: USGS geologic map data identifying rock and soil types with known radon-producing potential

These three data layers were combined at the county level to produce the zone assignments. The map has not been substantially revised since 1993, despite significant improvements in radon testing data availability. Some researchers have noted that the 1993 map may underpredict Zone 1 designation in certain geologic regions based on more recent measurement data.

Critical Limitation: County Averages vs. Individual Homes

The most important thing to understand about the radon zone map is what it cannot tell you: your home’s actual radon level. The map assigns zones based on county-level averages. Within any county — including Zone 3 counties — individual homes can vary from 0.2 pCi/L to 50+ pCi/L depending on:

• Local soil type and permeability (sandy soils allow faster radon movement than clay)
• Local bedrock uranium content (a single granitic intrusion can elevate radon in a small cluster of homes surrounded by low-radon geology)
• Foundation type and construction quality (slab vs. basement vs. crawl space; sealed vs. cracked)
• Building pressure dynamics (stack effect, HVAC, ventilation rate)
• Proximity to the water table and seasonal moisture levels

EPA’s own guidance explicitly states: “Any home can have a radon problem. This means new and old homes, well-sealed and drafty homes, and homes with or without basements.” Zone designation is a statistical predictor of regional risk, not a predictor of individual home risk.

How to Find Your County’s Radon Zone

EPA’s radon zone map is available at epa.gov/radon/find-information-about-local-radon-zones-and-state-contact-information. The map is searchable by state, and each state’s zone assignments are listed by county. The EPA also links to state-specific radon contact information, which often includes more detailed local radon data than the federal county-level map.

Many state radon programs publish sub-county radon data — zip code level or census tract level — that provides more precise local risk information than the EPA’s county-level map. For the most accurate local picture, consult your state radon program’s data in addition to the EPA map.

Frequently Asked Questions

Does living in a Zone 3 county mean I don’t need to test for radon?

No. Zone 3 means your county has the lowest predicted average radon potential nationally — it does not mean individual homes in your county are free of radon risk. EPA recommends testing in all zones. Significant local radon elevations occur in Zone 3 counties due to localized geology, soil conditions, and construction factors that the county-level map cannot capture.

Is the EPA radon zone map accurate?

The map is accurate as a statistical predictor of county-level averages based on 1993 data — which was the best available methodology at the time. It is not accurate as a predictor of individual home radon levels. The map’s limitations are well-documented in the literature: some counties are misclassified relative to more recent measurement data, and county-level averaging obscures significant within-county variation. Use it as context, not as a substitute for testing.

What does Zone 1 mean for new construction?

EPA recommends RRNC (Radon-Resistant New Construction) for all new homes in Zone 1 counties. Some states mandate RRNC for Zone 1 construction regardless of whether the specific site has been tested. HUD requires radon testing and mitigation for federally assisted multifamily projects in Zone 1. Even where not mandated, RRNC is strongly advisable in Zone 1 — the cost during construction ($350–$700) is a fraction of post-construction remediation ($800–$2,500).