Radon in Iowa Basements: The Published Numbers

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

Iowa has the worst measured indoor radon in the United States, and the figures are not close. The state health agency publishes an Iowa average indoor level of 8.5 picocuries per liter of air against a national average of 1.3 pCi/L, and reports that the Iowa Radon Survey found the largest percentage of any state - 71.6 percent - of homes above the EPA's action level of 4 pCi/L. Every county in Iowa is classified Zone 1. None of that is a marketing claim. It is what the state publishes, and every number on this page is linked to the document it came from.

This matters for a basement finish for one blunt reason: radon is a soil gas, it enters through the lowest level of the house, and finishing a basement turns the room with the highest concentration into the room where people spend the most time. Nothing about framing and drywall changes the level in the air. It changes how many hours a week somebody breathes it. What follows is the published data - state averages, the EPA's own risk tables, the 2026 Iowa statute and what it does and does not cover, and the certification rules that govern who is allowed to test and mitigate for hire in this state.

How does Iowa compare with the rest of the country?

The gap between Iowa and the national picture is a factor of roughly six on the average indoor reading, and it is a function of geology rather than housing. Glacial deposits across the state carry uranium-bearing material, and the soil gas produced by its decay moves into houses through footing joints, sump openings, floor cracks and utility penetrations. The practical consequence for a homeowner is that the national rules of thumb understate the problem here. A reading that would be unusual in most states is close to routine in central Iowa, which is why the state publishes a home buyer and seller fact sheet on the subject at all.

Iowa figures from Iowa HHS; U.S. averages and the national death estimate from EPA's A Citizen's Guide to Radon.

What risk does the EPA attach to a given reading?

The EPA publishes lifetime lung cancer risk per 1,000 people at fixed radon levels, split by smoking history, in A Citizen's Guide to Radon. The split is the striking part: at every level, the risk for someone who has smoked is several times the risk for someone who never has, because radon and tobacco smoke compound each other. The guidance column is the agency's own recommendation at each level - fix at 4 pCi/L and above, consider fixing between 2 and 4. Read the table against the Iowa average of 8.5 pCi/L and the state's position becomes obvious without anyone editorializing about it.

Lifetime risk of lung cancer death per 1,000 people at each level, from EPA's A Citizen's Guide to Radon.

What did Iowa actually pass in 2026?

House File 2297 created a new Iowa Code section 103A.8E, requiring that new single-family or two-family residential construction include a passive method for the mitigation of radon listed in appendix AF of the International Residential Code, 2021 edition. A companion amendment to section 103A.10 makes the state building code's radon provisions applicable to all new single-family and two-family residential construction in Iowa, closing the usual gap between cities that adopt a code and cities that do not. The bill's own text limits it to construction commenced after the adoption of the requirement, which is why it does nothing for an existing house.

Recorded actions from the Iowa Legislature's bill history for HF 2297, 91st General Assembly.

Who is allowed to test or mitigate radon in Iowa?

Iowa Code chapter 136B governs this, and the rule is short. Section 136B.1(3) provides that a person who is not certified, as appropriate, shall not test for the presence of radon gas and radon progeny, and a person who is not credentialed, as required, shall not perform abatement measures. That is a licensing rule with teeth attached: section 136B.5 makes a violation of the chapter a serious misdemeanor. It applies to the person doing the work for hire, not to the homeowner deciding what work to have done.

The chapter carves out two exemptions that homeowners use constantly. It does not apply to a person performing the testing or abatement on a building which the person owns, and it does not apply to a person performing testing or abatement without compensation. So a do-it-yourself short-term test kit in your own basement is entirely lawful, and so is a neighbor helping for free. Paying someone uncertified to install a mitigation system is not. When you collect quotes for a system ahead of a basement finish, ask for the credential before you ask for the price.

What do these numbers change about finishing a basement?

Sequence, mostly. A short-term test costs very little and takes days, and it has to happen before the walls go up rather than after, because the cheapest time to run a mitigation stack is when the slab, the sump and the rim joist are all still exposed. Retrofitting the same system into a finished room means cutting drywall, chasing pipe through a soffit you just paid for, and finding a discharge route that does not run through the middle of a new theater wall. The order that saves money is test, decide, mitigate if needed, then frame.

It also changes how you think about the room's purpose. A basement bedroom or a home office is occupied for thousands of hours a year; a storage room and a laundry are not. With an Iowa average of 8.5 pCi/L and 71.6 percent of tested homes above the action level, the odds that a given central Iowa basement reads high are better than even. That is not a reason to skip the project. It is a reason to spend a small amount on a test kit before spending a large amount on finishes, and to know the answer before a bedroom door goes on.

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. Iowa HHS - Radon Home Buyers and Sellers Fact Sheet — Iowa average of 8.5 pCi/L, national average of 1.3 pCi/L, the 4 pCi/L action level, Zone 1 classification for all Iowa counties, and approximately 400 radon-attributed deaths a year in Iowa.
2. Iowa HHS - Radon Resources — The Iowa Radon Survey finding that Iowa has the largest percentage of any state, 71.6 percent, of homes above the EPA action level of 4 pCi/L.
3. EPA - A Citizen's Guide to Radon — The lifetime risk table by smoking history, the EPA guidance column, the 0.4 pCi/L average outdoor level, and the estimate of about 21,000 radon-related lung cancer deaths per year nationally.
4. Iowa Legislature - HF 2297 Bill History — Every date and vote in the legislative timeline table, including the May 19, 2026 signing and the Acts chapter 1124 citation.
5. Iowa Legislature - HF 2297 Enrolled Text — The text of new Iowa Code section 103A.8E, the reference to appendix AF of the 2021 IRC, and the limitation to construction commenced after adoption.
6. Iowa Code Chapter 136B - Radon Testing and Abatement — Section 136B.1(3) certification and credentialing requirements, the owner-performed and uncompensated exemptions, and the serious misdemeanor penalty at section 136B.5.
7. Iowa Administrative Code 481-301 - State Building Code — Rule 481-301.8 adopting the 2024 International Residential Code as the state building code, including the emergency escape opening requirements at section R319.