Radon Map USA: What Homeowners Need to Know
The radon map of the USA is the picture most people see first when they start researching radon. The EPA’s national map sorts every county into one of three zones based on the predicted indoor radon level, giving a broad sense of where the gas is most common. It is a useful planning tool, but it has real limits, and the most important one is that it cannot tell you about your specific house. This guide summarizes EPA and CDPHE guidance current as of 2026 for Front Range homeowners. It is educational only; consult a certified radon professional for testing and a physician about any health concerns.
What Is the Radon Map of the USA?
The EPA’s radon map of the USA divides counties into three zones based on average predicted indoor radon levels. It was developed to help governments and homeowners understand regional radon potential and to target awareness efforts and building-code requirements. The three zones are:
- Zone 1 (red) — highest potential, predicted average at or above 4.0 pCi/L
- Zone 2 (orange) — moderate potential, predicted average between 2.0 and 4.0 pCi/L
- Zone 3 (yellow) — lowest potential, predicted average below 2.0 pCi/L
The map reflects geology, soil characteristics, and existing test data aggregated to the county level. It is a generalization by design, not a measurement of any individual home, and the EPA itself notes that all homes should be tested regardless of zone. To translate the map’s zones into what a reading actually means for your health and your wallet, pair it with our guide to radon levels.
Where Does Colorado Fall on the Map?
Colorado is heavily red. Most of the state, including the entire Front Range corridor, sits in Zone 1, the highest-potential category. Counties such as Denver, Boulder, Jefferson, Douglas, Arapahoe, Adams, Broomfield, and El Paso are classified Zone 1, meaning the predicted average indoor level is at or above the EPA action level of 4.0 pCi/L.
This reflects the region’s uranium-bearing geology and mountain soils, which generate more radon than many other parts of the country. For Front Range homeowners, the map is essentially a flashing signal to test, not a reassurance to skip it. Seeing your county shaded red is the strongest possible argument for placing a test in your lowest livable space. Our pillar on radon testing in Colorado explains why the local geology drives such high classifications across the region.
How to Read the Map Correctly
The zones describe the odds, not your destiny. A Zone 1 county means a high share of homes test elevated, but plenty of individual homes there read low. A Zone 3 county means lower average potential, but it still contains homes with dangerous readings. The EPA is explicit on this point: the map should not be used to decide whether to test, because every home should be tested regardless of zone.
Use the map to gauge urgency and set expectations, not as a substitute for a test. Radon depends on the soil under your specific lot and how your house is built and operated, which is why two neighbors can get very different results despite sharing the same map color. The map is a regional weather forecast; a test is the actual temperature at your front door. For a finer-grained but still imperfect view, see our guide to radon levels by zip code.
Why the Map Cannot Replace a Test
Radon enters through the foundation, drawn in by the pressure difference between a heated home and the cooler ground. The amount that gets in depends on factors no county-level map can capture:
- The exact soil and rock beneath your lot
- Foundation type, cracks, and penetrations
- Sump pits, crawl spaces, and drainage
- How the home is sealed and ventilated
- Recent renovations that change airflow or open new pathways
Because of these variables, a map zone is a starting point, not an answer, and relying on it alone is the most common way homeowners talk themselves out of a worthwhile test. Our explainer on how radon gets into homes shows why house-level details outweigh regional averages every time.
Using the Map for Buying or Building
The radon map is genuinely helpful at the planning stage. If you are buying in a Zone 1 area like the Front Range, expect to test and budget for possible mitigation as a normal part of the transaction. If you are building new, the map supports the case for installing radon-resistant features during construction, which is far cheaper than retrofitting later. Many builders in high-zone areas already include passive radon piping that can be activated with a fan if a post-construction test comes back high. Knowing your county’s zone before you build or buy lets you plan rather than react.
What to Do After Checking the Map
Whatever your zone, the next step is the same: test your home. Place a short-term test in the lowest livable area for a quick estimate, or a long-term test for a year-round average that accounts for seasonal swings. If your result is at or above 4.0 pCi/L, the EPA recommends mitigation, typically an active soil depressurization system that reliably lowers levels well below the action level. After mitigation, a follow-up test confirms success. Retest every couple of years and after major renovations, since levels change over time even in a home that once tested low.
How the EPA Built the Radon Map
Understanding how the map was made clarifies both its value and its limits. The EPA developed the zone map using indoor radon measurements collected across the country, geologic data on uranium and soil characteristics, and other predictive factors. The agency then assigned each county to a zone based on the predicted average indoor radon level for that area. It was designed primarily to help state and local governments target resources and to inform building codes, not to advise individual homeowners on whether to test.
That origin explains why the map paints with such a broad brush. A county is a large area, and a single zone color cannot capture the variation between one lot and the next within it. The map is a planning instrument built from averages and geology, which makes it excellent for regional decisions and poor for predicting any one home. Knowing this, a homeowner can use the map for what it does well, gauging regional risk, while recognizing that it was never meant to replace a measurement of their own house.
Other Radon Maps and Tools
The EPA zone map is the best-known reference, but it is not the only tool available, and the others have their own strengths and weaknesses. State radon programs often publish more detailed data, sometimes down to the county or zip-code level, drawn from local test results. Some maps show the percentage of tested homes that exceeded 4.0 pCi/L, which can feel more concrete than a three-zone classification.
A few cautions apply to all of these tools:
- More granular maps still describe areas, not individual homes
- Areas with little testing may show unreliable averages
- Newer data may differ from the older national zone map
- No map accounts for your specific foundation and how you operate the house
The common thread is that every map, however detailed, remains a regional estimate. They are useful for orientation and planning, and Colorado’s data consistently confirms the Front Range as high-risk, but the only tool that measures your home is a test placed in your lowest livable space.
When to Call a Professional
Call a certified radon professional if a test reads at or above 4.0 pCi/L, if you are buying or selling, or if you want a dependable long-term measurement rather than relying on the map. The radon map of the USA tells you the regional odds and is a fine place to begin your research, but a measurement of your own home and, where needed, a professionally installed mitigation system are what actually protect your household over the long run. For Zone 1 Front Range homes, testing is not optional, and the map’s red shading is precisely the reason why. Think of the map as the opening line of the conversation rather than the conclusion: it establishes that the region carries real radon potential, and the test you place in your own home finishes the thought by telling you exactly where you stand. Read in that order, the map and the test complement each other, with the map setting expectations and the measurement delivering the answer that actually drives your decisions.
How Builders and Codes Use the Map
The radon map’s most appropriate use is not by individual homeowners deciding whether to test, but by the people who set building codes and plan construction. In high-zone areas, many jurisdictions require or encourage radon-resistant new construction, which bakes prevention into a home from the start. These features include a gas-permeable layer beneath the slab, a vapor barrier, sealed foundation openings, and a vent pipe routed from below the slab to above the roof, sometimes with the wiring in place to add a fan later.
Installing these elements during construction costs a fraction of retrofitting an existing home, which is exactly the kind of decision the zone map is designed to inform. A builder working in a Zone 1 county like those across the Front Range can reasonably treat radon-resistant construction as standard practice. For a buyer of new construction in the region, asking whether the home includes passive radon piping is a smart question, since that piping makes any future mitigation simpler and cheaper. The map, in this sense, does its best work upstream, shaping how homes are built rather than telling a homeowner whether to test, which they should do regardless.
Common Misreadings of the Radon Map
The radon map is widely shared but just as widely misinterpreted, and a few recurring errors lead homeowners astray. Because the map is so visual and easy to glance at, people tend to draw firmer conclusions from it than the data supports. The misreadings worth avoiding include:
- “My county is Zone 3, so I am safe.” Zone 3 still contains homes with dangerous readings; the zone is an average, not a guarantee.
- “My county is Zone 1, so my home is definitely high.” Plenty of Zone 1 homes read low; only a test confirms yours.
- “The map is current.” The national zone map is built on older data and may not reflect newer local findings.
- “The map covers my exact address.” It describes a whole county, not your lot.
The through-line is that the map answers a regional question and people keep trying to make it answer a personal one. For Front Range residents, the practical reading is simple and consistent: the map shows the region is high-risk, which is a strong prompt to test, and the test then provides the address-specific answer the map cannot. Used as a starting signal rather than a final word, the map does its job well. Treated as a substitute for testing, it becomes the very thing that leads homeowners to skip the one step that actually protects them.
References
- EPA Map of Radon Zones — U.S. Environmental Protection Agency
- Colorado Radon Zones and Risk — Colorado Department of Public Health and Environment
- What Is Radon Gas and Is It Dangerous — U.S. Environmental Protection Agency
- Radon Risk Across the U.S. — American Lung Association
The map shows the Front Range is high-risk; a test shows your actual number. If you want a measurement for your specific home, reach out through our contact page for a vetted local radon professional.