Iowa Radon Facts
Iowa Radon Facts: Why Iowa Has the Highest Radon in the US
Iowa leads the nation in indoor radon, and the reasons are geological, measurable, and consequential for health. Here is what the science and the regulators actually say, with every figure tied to its source.
The short answer
Iowa has the highest indoor radon in the US because its glacial soils and, in the northeast, fractured Driftless Area limestone let radon move easily into homes. The state average is about 8.5 pCi/L per Iowa HHS, all 99 counties are EPA Radon Zone 1, and roughly 71.6% of homes test above the 4 pCi/L action level.
Why Iowa Leads the Nation in Radon: The Geology
Radon is a colorless, odorless radioactive gas produced as uranium in soil and rock breaks down. Whether it ends up inside a home depends on two things, how much uranium-bearing material sits beneath the house and how easily the gas can travel through the ground. Iowa scores high on both, and it does so through two very different geologic stories.
Most of Iowa: glacial till that lets radon flow
The majority of Iowa was repeatedly covered by glaciers during the Ice Age. As those glaciers advanced and retreated, they ground bedrock into a deep blanket of fine, mixed sediment known as glacial till. That till is rich in the uranium and radium that decay into radon, and because it is finely ground and loosely packed, it is permeable. Radon generated deep in the soil can migrate upward through it and collect under the slabs and in the basements of homes built on top. Across central, northern, and western Iowa, including the Sioux City area, this glaciated terrain is the main reason indoor levels run so high.
Northeast Iowa: the Driftless Area and karst limestone
The far northeast corner, the country around Dubuque, tells the opposite story. This is the unglaciated Driftless Area, also called the Paleozoic Plateau, a region the glaciers largely missed. Instead of deep till, the bedrock here is Paleozoic limestone and dolomite that is heavily fractured, with sinkholes, caves, and the dissolved-rock features known as karst. Those fractures and voids act like chimneys, giving radon a direct, fast path from the bedrock straight into the foundations above. So while the mechanism differs, glacial permeability in most of the state and karst fracturing around Dubuque, both routes deliver the same result, elevated radon in Iowa homes.
The Numbers, Each One Sourced
Iowa is not a marginal case. The data put it at the top of the national radon map. The state average indoor level is about 8.5 pCi/L according to Iowa HHS, compared with a US average of roughly 1.3 pCi/L. Around 71.6% of Iowa homes have tested above the EPA action level of 4 pCi/L per the Iowa Radon Survey reported by Iowa HHS, and the EPA places all 99 Iowa counties in Radon Zone 1, its highest-risk category. There is no low-risk pocket of the state where testing can be safely skipped.
Key Iowa Radon Facts
| Fact | Detail | Source |
|---|---|---|
| Iowa average indoor radon is about 8.5 pCi/L | Roughly six to seven times the US average of about 1.3 pCi/L. | Iowa HHS |
| About 71.6% of Iowa homes test above 4 pCi/L | Nearly three in four homes sit at or above the EPA action level. | Iowa Radon Survey / Iowa HHS |
| All 99 Iowa counties are EPA Radon Zone 1 | Zone 1 is the highest-risk designation, predicted average above 4 pCi/L. | EPA |
| Radon is the #2 cause of lung cancer after smoking | Linked to about 21,000 lung cancer deaths per year in the US. | EPA |
| About 400 Iowans die of radon-related lung cancer per year | A state-level estimate for Iowa specifically. | American Cancer Society Cancer Action Network |
| The EPA action level is 4.0 pCi/L | There is no risk-free level, so lower is always better. | EPA |
| Mitigation systems reduce radon by 50 to 99% | When properly installed, per the EPA. | EPA |
Sources: US EPA, Iowa Department of Health and Human Services (Iowa HHS), the Iowa Radon Survey, and the American Cancer Society Cancer Action Network. Verify current figures with each agency.
The Health Stakes
Radon matters because of what long-term exposure does to the lungs. The EPA identifies radon as the second leading cause of lung cancer in the US after smoking, and links it to about 21,000 lung cancer deaths every year nationwide. The risk is not theoretical for Iowa. The American Cancer Society Cancer Action Network estimates that roughly 400 Iowans die of radon-related lung cancer each year.
The risk builds quietly over years of breathing elevated levels, which is why radon is so easy to ignore. There is no smell, no taste, and no immediate symptom. The only way to know a home's level is to test, and the good news is that radon is one of the most fixable environmental hazards a homeowner can face.
If you want a fuller picture of the risk, see our guide on whether radon is dangerous in Iowa.
The EPA Standard
The EPA sets the action level for radon at 4.0 pCi/L. At or above that level, the EPA recommends fixing the home. It is important to understand what the action level is and is not. It is a practical threshold for when action is clearly warranted, not a line below which radon is harmless. The EPA is explicit that there is no risk-free level of radon, so the agency notes that homeowners may also consider action between 2.0 and 3.9 pCi/L, and lower is always better.
The encouraging part is how effective fixing a home can be. Properly installed systems typically reduce radon by 50 to 99% according to the EPA. The most common approach, active sub-slab depressurization, uses a fan and a vent pipe to draw radon out from beneath the foundation and release it safely above the roofline.
To see what your own test number means, try our radon action level calculator, or read our guide to radon mitigation cost in Iowa.
The Iowa Credentialing Standard
Radon work in Iowa is regulated. Radon mitigation specialists are credentialed by the Iowa Department of Health and Human Services (Iowa HHS), which recognizes training from the National Radon Proficiency Program (NRPP) and the National Radon Safety Board (NRSB). If you have seen older references to the Iowa Department of Public Health, note that it merged into Iowa HHS on July 1, 2023, so Iowa HHS is the current credentialing body.
This is why credentials matter when you hire. Iowa Radon Professionals is a marketing and lead-routing service, not a contractor, so we do not test or install anything ourselves. What we do is connect you with an NRPP-certified, Iowa HHS-credentialed specialist who can do the work properly. For help evaluating a contractor, see our guide on choosing an Iowa radon contractor.
HF 2412: The Gail Orcutt Radon School Safety Act
Iowa has also acted on radon in its schools. HF 2412, the Gail Orcutt Radon School Safety Act, requires every Iowa school attendance center to test for radon by July 1, 2027 and every five years after that. The law is named for an Iowa teacher who died of radon-related lung cancer, and it reflects a broader recognition that the places Iowans spend the most time, homes and schools, are exactly where radon exposure adds up. See our full guide to the Iowa school radon mandate (HF 2412) for the testing deadlines, re-test rules, and the new 2026 radon code for homes.
For families, the school mandate is a useful prompt. If the buildings where children spend their days are now required to test, the home where they sleep deserves the same attention.
What to Do About Radon in Your Iowa Home
Given the numbers, the path forward is straightforward. First, test. With about 71.6% of Iowa homes above the action level per Iowa HHS and all 99 counties in EPA Radon Zone 1, testing is the only way to know where your home stands. Short-term test kits are widely available, and county health departments often offer them.
Second, if your result is at or above 4.0 pCi/L, mitigate. That is the point at which the EPA recommends fixing the home, and properly installed systems typically reduce radon by 50 to 99% according to the EPA. Use an NRPP-certified, Iowa HHS-credentialed specialist so the system is sized, sealed, and tested correctly.
We can connect you with a credentialed specialist for a free, no-obligation quote, whether you are in Sioux City, Dubuque, or anywhere else in Iowa. You can also reach out directly to get started.
Frequently Asked Questions
Why does Iowa have the highest radon in the US?
Iowa combines two radon-favorable geologies. Most of the state is covered by glacial till, fine and permeable ground-up bedrock and soil that lets radon migrate easily toward homes. Northeast Iowa around Dubuque is the unglaciated Driftless Area, where fractured limestone and karst give radon a direct path to the surface. The result, per Iowa HHS, is a state average around 8.5 pCi/L, well above the US average of about 1.3 pCi/L.
What percentage of Iowa homes have high radon?
About 71.6% of Iowa homes tested above the EPA action level of 4 pCi/L, according to the Iowa Radon Survey reported by Iowa HHS. That is nearly three out of four homes, which is why testing is recommended for every Iowa home regardless of county.
What is the EPA radon action level?
The EPA action level is 4.0 pCi/L. At or above that level, the EPA recommends fixing the home. There is no completely risk-free level of radon, so the EPA notes that homeowners may also consider action between 2.0 and 3.9 pCi/L.
How dangerous is radon in Iowa?
Radon is the second leading cause of lung cancer after smoking and is linked to about 21,000 deaths per year in the US, according to the EPA. The American Cancer Society Cancer Action Network estimates roughly 400 Iowans die of radon-related lung cancer each year. Because Iowa radon levels are the highest in the nation, the risk here is elevated, which is why testing is so important.
Who credentials radon mitigation specialists in Iowa?
Radon mitigation specialists in Iowa are credentialed by the Iowa Department of Health and Human Services (Iowa HHS), which recognizes National Radon Proficiency Program (NRPP) and National Radon Safety Board (NRSB) training. The former Iowa Department of Public Health merged into Iowa HHS on July 1, 2023, so the current credentialing body is Iowa HHS.
Do Iowa schools have to test for radon?
Yes. HF 2412, the Gail Orcutt Radon School Safety Act, requires every Iowa school attendance center to test for radon by July 1, 2027 and every five years after that. The law was named for an Iowa teacher who died of radon-related lung cancer.
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