Category: Regulations & Certification

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).

The United States does not have a single federal radon law. Instead, radon regulation in America is a patchwork of federal guidelines, state licensing and disclosure laws, building code requirements, and voluntary programs — each operating independently. Understanding this structure explains why radon requirements differ dramatically between states, why some transactions require certified professionals while others do not, and why “federal radon law” is largely a misnomer.

Federal Radon Framework: Guidelines, Not Mandates

At the federal level, the EPA is the primary radon authority. The EPA’s radon program operates almost entirely through guidance, technical assistance, and voluntary programs — not regulatory mandates. Two federal statutes form the legal foundation:

Indoor Radon Abatement Act (IRAA) of 1988

The Indoor Radon Abatement Act, enacted as Title III of the Toxic Substances Control Act (TSCA), established the federal policy framework for radon. Key provisions:

• Declared that the national long-term goal is reducing indoor radon to outdoor levels (~0.4 pCi/L)
• Directed EPA to publish technical guidance and establish a radon measurement proficiency program
• Authorized grants to states for radon programs, technical assistance, and public education
• Directed EPA to develop model construction standards for radon-resistant new construction
• Did not establish mandatory testing requirements, mandatory action levels, or federal licensing requirements for contractors

Residential Lead-Based Paint Hazard Reduction Act of 1992 (Title X)

Title X of the Housing and Community Development Act included radon provisions affecting federally assisted housing. It directed HUD to develop radon testing and mitigation requirements for HUD-assisted housing in high-radon areas and required disclosure of known radon hazards in federally assisted housing transactions.

EPA’s Role: Guidance Authority

EPA’s primary radon tools are guidance documents, technical standards, and voluntary programs:

• EPA Action Level (4.0 pCi/L): EPA’s recommended action level for mitigation. It is a guidance value, not a regulatory standard — there is no federal penalty for having a home above 4.0 pCi/L, and no federal requirement to test or mitigate.
• EPA Radon Measurement Proficiency (RMP) Program: Established the original framework for certifying radon measurement professionals. Now administered through NRPP (AARST) and NRSB as independent certification bodies.
• State Indoor Radon Grants (SIRG): EPA provides annual grants to state radon programs under IRAA. These grants fund state testing programs, contractor certification, public outreach, and radon-resistant new construction promotion.
• Radon Zone Map: EPA’s Map of Radon Zones designates all U.S. counties as Zone 1 (highest potential, predicted average above 4.0 pCi/L), Zone 2 (moderate, 2.0–4.0 pCi/L), or Zone 3 (lowest potential, below 2.0 pCi/L). The map informs but does not compel action.

State Authority: Where Regulation Actually Happens

States are the primary regulatory actors in radon. Through their police powers over public health, states have enacted a wide range of radon-specific laws:

Contractor Licensing

Approximately 20+ states require radon professionals to hold a state license or certification to legally conduct radon measurement or mitigation. Requirements vary significantly:

• Some states (e.g., New Jersey, Pennsylvania, Florida) have comprehensive licensing programs with examination, continuing education, and liability insurance requirements
• Some states accept NRPP or NRSB national certification as sufficient
• Some states require state-specific licensing in addition to national certification
• States without licensing requirements allow anyone to conduct radon work — no examination or certification needed

Real Estate Disclosure

Many states have enacted radon disclosure requirements for real estate transactions. Common structures:

• Known results disclosure: Sellers must disclose any known radon test results (Florida, Illinois, Maine, and others)
• Mitigation system disclosure: Sellers must disclose the presence of an existing radon mitigation system
• EPA pamphlet distribution: Some states require providing the EPA “Home Buyer’s and Seller’s Guide to Radon” to buyers
• No specific radon disclosure law: The general material defect disclosure duty under real estate law may cover known elevated radon in most states even without a specific radon statute

School and Public Building Requirements

Illinois, New Jersey, Pennsylvania, and several other states require radon testing in schools and/or childcare facilities. Requirements differ in frequency, action levels, and who conducts testing.

Rental Property Requirements

Some states with high radon prevalence have enacted landlord disclosure or testing requirements for rental properties. These are typically narrower in scope than homeowner requirements and vary substantially between states.

Building Codes: The RRNC Adoption Map

Radon-Resistant New Construction (RRNC) is addressed in the International Residential Code (IRC), which most U.S. jurisdictions have adopted in some form. The IRC includes an appendix (Appendix F) with RRNC requirements — but appendices are optional, and adoption varies by state and locality:

• Some states mandate IRC Appendix F adoption statewide for high-radon counties
• Some counties and municipalities in non-mandating states have adopted RRNC locally
• Many jurisdictions have adopted the IRC base code but not the RRNC appendix — RRNC is not required even though a general building code exists

States with statewide RRNC mandates or strong local adoption include portions of Colorado, Iowa, Maryland, Minnesota, Montana, North Dakota, and South Dakota — all Zone 1 states. Even in these states, enforcement varies by jurisdiction.

HUD and Federally Assisted Housing

The U.S. Department of Housing and Urban Development (HUD) has established radon requirements for multifamily housing projects receiving federal assistance. HUD’s Office of Lead Hazard Control and Healthy Homes (OLHCHH) administers radon policy for HUD-assisted properties:

• Properties in EPA Zone 1 counties receiving certain HUD assistance must test for radon
• Properties exceeding 4.0 pCi/L must mitigate before or shortly after occupancy
• New HUD-assisted multifamily construction in Zone 1 must incorporate RRNC features

Frequently Asked Questions

Is there a federal law requiring radon testing in homes?

No. The Indoor Radon Abatement Act of 1988 established federal radon policy and directed EPA to develop guidance and voluntary programs, but it does not mandate testing in private residences. Radon testing requirements for homeowners, if any, come from state law — and most states do not mandate testing in owner-occupied residences.

Which level of government regulates radon contractors?

States regulate radon contractors. There is no federal radon contractor licensing requirement. Approximately 20+ states require state licensing or accept national certification (NRPP or NRSB) for radon measurement and/or mitigation work. In states without contractor regulation, anyone can legally perform radon work regardless of training.

Does EPA set legally binding radon limits?

No. EPA’s 4.0 pCi/L action level is a guidance recommendation, not a legally binding regulatory standard. There is no federal penalty for radon levels above 4.0 pCi/L in a private residence, no federal requirement to remediate, and no federal enforcement mechanism for residential radon. The action level guides voluntary decisions and state programs, but it is not a regulatory threshold with legal consequences in the same way that OSHA exposure limits or EPA ambient air standards are.