Radon Levels by Zip Code Colorado: What to Know
Searching for radon levels by zip code Colorado is a sensible instinct, but the results come with an important caveat: zip-code averages describe a broad area, not your specific house. Colorado sits in a high-radon region, and many counties fall into the EPA’s highest-potential zone, yet two homes on the same street can test very differently. This guide summarizes EPA and Colorado Department of Public Health and Environment guidance current as of 2026. It is educational only and does not diagnose any condition; only an in-home test, interpreted with a certified professional, tells you your actual level.
What do radon levels by zip code in Colorado tell you?
Zip-code and county radon data provide a regional risk estimate, useful for understanding general likelihood but not your home’s true reading. Colorado is one of the highest-radon states in the country, and a large share of homes tested statewide come back above the EPA action level of 4 picocuries per liter. Front Range counties including Denver, Jefferson, Douglas, Boulder, El Paso, Arapahoe, and Adams all sit in areas with significant radon potential, and the same holds for surrounding counties along the corridor.
The EPA classifies counties into radon zones, and most of Colorado’s populated areas fall into Zone 1, the highest-potential category. That classification means elevated radon is common, not guaranteed, in any given home. The data is a prompt to test, not a substitute for testing. The county-level mapping framework is explained in the guide on the EPA map of radon zones, which shows how these regional estimates are built from indoor measurements and geology rather than from address-specific readings.
Why can’t zip-code data tell you your home’s level?
Radon enters a home from the soil and rock beneath it, and the amount that accumulates indoors depends on factors unique to each structure. Two neighboring houses can have very different readings because of differences in foundation type, cracks and openings, soil composition directly underneath, construction quality, and ventilation. Averaged zip-code data smooths over all of that local variation.
Home-specific factors
Foundation design matters a great deal. A home with a basement, a sump pit, or extensive slab cracks may draw in more soil gas than a slab-on-grade house nearby. Negative indoor air pressure, common in tightly sealed modern homes, can pull radon up from the soil. Even the same home can read differently from one season to the next as the ground freezes and thaws and as windows stay shut through Colorado winters, when readings often run higher than in summer.
Because of this variability, a low neighborhood average offers no guarantee, and a high one does not doom a particular house. Geology and construction interact to produce a home’s actual level, which is why the only dependable answer comes from testing the specific structure.
How should Colorado homeowners use the data?
Treat zip-code and county radon information as a reason to take testing seriously, especially given Colorado’s high-radon designation. If you live in a Zone 1 county, which covers most of the Front Range, the regional data strongly suggests testing your own home rather than assuming you are in the clear. The map tells you the odds are meaningful; the home test tells you your reality.
The practical step is straightforward: test your home directly. A short-term test kit can give a quick reading in a few days under closed-house conditions, while a long-term test over 90 days or more gives a more representative average that accounts for seasonal swings between summer and winter. The EPA recommends testing every home below the third floor regardless of zip code. Test kits are inexpensive and widely available, and following the placement and duration instructions carefully produces a reliable result you can act on.
What level should prompt action?
The EPA action level is 4 picocuries per liter. A home that tests at or above 4 pCi/L should have a mitigation system installed to reduce the level. The EPA also notes that radon risk exists below 4 pCi/L and that homeowners may consider reducing levels between 2 and 4 pCi/L, since no amount of radon is entirely without risk. The action level is a threshold for recommended action, not a hard line between safe and unsafe.
If a test comes back above the action level, the next step is mitigation, typically a sub-slab depressurization system that vents soil gas safely above the roof. These systems reliably bring radon well below 4 pCi/L in most Colorado homes. The mitigation process and what a finished system looks like fit within the broader Colorado radon testing overview, which frames testing and reduction together.
Which Front Range areas show elevated radon?
Across the Colorado Front Range, elevated radon is the rule rather than the exception, which is why the state ranks among the highest-radon in the country. The counties along the urban corridor, including Denver, Jefferson, Boulder, Douglas, Arapahoe, Adams, El Paso, Larimer, and Weld, all sit in areas with substantial radon potential. Many homes in these counties test above the EPA action level of 4 picocuries per liter, and statewide data consistently places Colorado among the states with the highest share of elevated readings.
The geology behind this is consistent. The soils and rock of the region contain uranium that decays to produce radon, and the gas migrates upward into homes through foundation cracks and openings. Because the underlying conditions are widespread, no Front Range community can be assumed safe based on location alone. A home in a high-potential county may still test low, and a home in a slightly lower-potential area may test high, which again points back to the necessity of testing each home individually rather than relying on the county average.
Why neighbors can differ
Even within a single neighborhood, readings vary house to house. The amount of radon that accumulates depends on the specific soil directly beneath a foundation, the design and tightness of that foundation, the presence of a basement or sump, and the home’s ventilation and air-pressure dynamics. Two homes built by the same builder on adjacent lots can return very different numbers. This is the core reason zip-code averages, however accurate as regional descriptions, cannot stand in for a measurement of a particular house.
How accurate is radon-zone mapping?
The EPA’s radon-zone map and similar county-level resources are built from indoor measurements, geology, and other data to estimate average potential across an area. They are genuinely useful for understanding where elevated radon is more likely and for guiding public-health messaging. What they cannot do is predict any individual home’s level, because the map describes averages rather than specific structures.
Treating the map as a screening tool rather than a verdict is the right approach for any homeowner. A Zone 1 designation, which covers most of the Front Range, means elevated radon is common and testing is strongly warranted. It does not mean every home will test high, nor does a lower-potential area guarantee a safe reading. The map raises or lowers the prior probability, and the home test resolves the actual question for a particular address. This distinction between regional estimate and individual measurement is the single most important idea for anyone researching radon by location.
Homeowners should also be cautious about online tools that promise a precise radon level for a specific address. No map or database can deliver that, because the data underlying these tools is regional and the factors that determine a home’s level are local to the structure. The only reliable number comes from a test conducted inside the home itself, ideally following EPA testing protocols for placement and duration.
When does radon testing matter most?
Testing is especially important during a real estate transaction, when a buyer is committing to a home for years. Radon testing is a common and inexpensive add-on to a pre-purchase inspection, and in Colorado’s high-radon environment it is among the most worthwhile. A reading above 4 pCi/L can be addressed before closing, often with the seller funding mitigation as part of the negotiation. Because mitigation is reliable and reasonably priced, a high radon result rarely needs to derail a purchase; it simply becomes a point to resolve before the keys change hands.
Existing homeowners should test too, particularly if they have never tested or have finished a basement into living space. Radon levels can change over time as a home settles, as renovations alter airflow, and as the surrounding soil shifts. Periodic retesting, every few years and after major construction, keeps the picture current.
What should you do with your test result?
Interpreting a home test result is straightforward once the number is in hand. A reading below 2 picocuries per liter is generally considered low, though the EPA notes that no level of radon is entirely without risk and exposure adds up over years. A reading between 2 and 4 pCi/L sits below the action level, but the EPA suggests homeowners may consider reducing it. A reading at or above 4 pCi/L is the action level, and the EPA recommends installing a mitigation system to bring it down.
If a test comes back high, the path forward is well established. A mitigation system, typically sub-slab depressurization, vents soil gas safely above the roof and reliably brings levels well below the action level in most Colorado homes. The repair process and what to expect are described in the guide on how to fix radon in a home. Because Colorado’s elevated radon is so common, mitigation contractors across the Front Range are experienced and readily available to homeowners.
A single short-term test is a useful first screen, but a confirmatory or longer-term test adds confidence before committing to mitigation. Short-term tests can be influenced by weather and how the home was operated during the test window, so a follow-up test, or a long-term test over 90 days or more, gives a more representative picture before a major investment like mitigation. The EPA’s testing protocols guide how to conduct these tests for dependable results, and following them closely matters as much as the device used.
Why location data still has value
None of this means zip-code and county radon data is useless. Its value lies in motivating action. For a Front Range homeowner who might otherwise assume radon is someone else’s problem, learning that their county sits in the EPA’s highest-potential zone is a powerful prompt to test. The regional data establishes that the risk is real and common in Colorado, even if it cannot pin down a specific home’s level on its own.
Used correctly, location data and a home test work together. The map tells you the odds are meaningful and testing is warranted; the home test tells you your actual exposure and whether mitigation is needed. Treating the two as complementary, rather than expecting the map to do the test’s job, leads to sound decisions. For Colorado households, that combination of regional awareness and individual measurement is the reliable path to managing radon risk.
The practical bottom line for anyone searching radon levels by zip code in Colorado is simple. Use the regional data to understand that elevated radon is common across the Front Range and that testing is strongly advised. Then test your own home to learn your real number, and act on a result at or above 4 pCi/L by arranging mitigation. That two-step approach, regional awareness followed by individual testing, converts a broad statistic into protection for your specific household, which is something no zip-code average alone can provide.
References
- Local Radon Zones and State Information — U.S. Environmental Protection Agency
- Radon Testing and Risk in Colorado — Colorado Department of Public Health and Environment
- Radon Health Risks — Centers for Disease Control and Prevention
Homeowners across the Denver metro and Front Range can get in touch through our contact page to connect with a vetted local professional for radon testing or mitigation.