Most advice about buying or selling in Iowa City repeats the same line: Iowa has a radon problem, so test the house. That's true, and it's also not very useful, because it treats every property in Johnson County as the same risk. The variable that actually predicts your exposure, and your leverage at the closing table, is a question almost nobody asks out loud: what year was this house built, and which construction rule was in force the day the foundation went in.
That question matters more this year than it has in a long time. On July 1, 2026, a new statewide building code took effect requiring passive radon mitigation systems in every new single- and two-family home built in Iowa. Johnson County and the city of Iowa City didn't wait for the state to catch up. They were already requiring it.
The Statistic Everyone Quotes, and Why It Doesn't Tell You Much
Iowa has the largest share of homes above the EPA's action level of any state in the country. Iowa's Department of Health and Human Services puts the average indoor radon reading statewide at 8.5 picocuries per liter, against a national average of 1.3, and reports that 71.6 percent of tested Iowa homes come in above the EPA's 4.0 action threshold.
That statistic is real and it's a good reason to test. It's a poor reason to assume anything about a specific address. It's a state average built from a mix of building eras, soil conditions and foundation types, and it flattens a distinction that matters a great deal if you're actually buying or selling in Iowa City this year: whether the home was built before or after a passive mitigation system was legally required where it stands.
Iowa City Was Ahead of the State, Not Behind It
Before the statewide code took effect, radon-resistant new construction was already mandatory in a specific, named list of Iowa jurisdictions: the counties of Bremer, Johnson, Linn and Polk, and the cities of Altoona, Bondurant, Carroll, Iowa City, North Liberty, Norwalk and Pella. Johnson County and Iowa City are both on that list. So is North Liberty, a few miles north.
That means a home built inside Iowa City limits after that local requirement took hold almost certainly has a passive radon system built into its foundation, a design choice that typically adds somewhere between $300 and $500 to the cost of new construction according to county building code guidance. That's a fixed line item baked in at the framing stage, not a retrofit installed after a bad test result. A buyer looking at a newer Iowa City build isn't guessing whether that protection exists. It was required before the state made it the law everywhere.
What Build Year Actually Tells You
| If the home was built... | What you can reasonably assume |
|---|---|
| Before Johnson County's radon-resistant construction rule | No passive system, unless a prior owner added one |
| After Johnson County's rule, before July 1, 2026 | Passive system required within Johnson County and Iowa City limits |
| After July 1, 2026, anywhere in Iowa | Passive system required under the new statewide building code |
This is the table that should replace "Iowa has a radon problem" in a buyer's mental model of Iowa City. A lot of Iowa City's housing stock, especially the Victorian and Craftsman-era homes downtown and on the Northside that predate any of these rules by close to a century, falls into that first row by default. That's not a defect. It's just a gap the new law doesn't reach, because the July 2026 code only governs new construction going forward. It does nothing for a house that's already standing.
What the Disclosure Law Actually Asks For
Iowa's property disclosure statute, Iowa Code chapter 558A, requires a seller to give a written disclosure statement to a buyer before an offer is accepted, covering known material conditions including environmental hazards like radon. Separately, under Iowa Code sections 543B.9 and 543B.18, administered by the Iowa Real Estate Commission, a seller must disclose the date and result of any radon test they know about and must provide the buyer with a copy of the state's official Radon Home Buyers and Sellers Fact Sheet, with the buyer signing to confirm they received it.
What none of that requires is a test before listing.
Iowa's disclosure law asks what a seller knows about radon. It does not ask what a seller tested for.
That distinction shows up in real Iowa City listings. It's common to see agent remarks stating the seller has no knowledge of radon, that the buyer may test at their own expense, and that the seller won't participate in mitigation or even be told the result. That language is legal. It should not be read as reassurance. It means the seller chose not to find out, and the law doesn't penalize that choice the way it would penalize hiding a known result.
If You're Buying an Older Iowa City Home
The practical move is a radon contingency written into your purchase agreement, not a passive request during the walkthrough. Testing itself is inexpensive: Johnson County Public Health sells short-term kits for $12 in person or $15 by mail, and long-term kits for $30 or $33. A licensed professional test typically runs somewhere in the same low range plus a service fee.
Timing matters too. The EPA recommends testing under closed-house conditions, windows shut, doors closed, because that's when radon has the least opportunity to disperse. Iowa's winter naturally produces those conditions without anyone trying. A test run in January or February on a closed-up house gives you a more honest baseline than the same test run in May with the windows cracked open. If you're closing on an older Iowa City home and the inspection period lands in a warm month, ask whether a short-term test under artificially closed conditions is being used, or push for it explicitly.
If you want a sense of what "older Iowa City home" actually spans architecturally, from the pre-war bungalows near downtown to the postwar ranches further out, our guide to Iowa City home styles breaks down what different building eras typically mean for buyers, radon exposure being one more thing that tracks with the calendar rather than the neighborhood.
If You're Selling
Testing before you list turns an unknown into a documented condition, and documented conditions are negotiable in a way surprises aren't. A seller who tests ahead of time and, if needed, installs mitigation and keeps the report, walks into showings with a number instead of a question mark. A seller who never tests is legally in the clear, but hands the buyer's inspector the opening to find the number for you, at a point in the transaction when you have far less control over the narrative.
If your home was built after Johnson County's local rule took effect, the passive system already in the foundation is worth stating plainly in your listing. It's a real cost you or a previous owner already absorbed, and it's the kind of detail a buyer comparing your house to an older one down the block will actually weigh.
The Question to Ask Before You Waive Anything
Skip "does Iowa have radon." Everyone already knows the answer. Ask instead when this specific house was built relative to Johnson County's rule and the statewide code that followed it in July. That answer tells you more about your actual risk, and your actual leverage, than any statewide average ever will.
A Few Straight Answers
Do I have to test for radon before selling my Iowa City home? No. Iowa law requires you to disclose radon test results you already have. It does not require you to run a test before listing.
If I'm buying new construction, does the July 2026 code mean the home is radon-free? No. A passive mitigation system reduces the risk of elevated radon, it doesn't guarantee a reading under 4.0 pCi/L. Test anyway, and treat a passive system as a head start rather than a finish line.
Does it matter what season I test in? Yes. Closed-house conditions produce more reliable readings, and Iowa winters create those conditions naturally. If your test happens during a warm month with windows open, ask about testing under closed conditions instead so the number you're negotiating around actually reflects the home's typical air exchange.
Whether you're weighing an older Northside bungalow against new construction on the edge of town, or trying to figure out what a radon disclosure actually protects you from, this is exactly the kind of local detail worth having an advisor for rather than a search engine. Blank & McCune has been reading Johnson County's building codes and disclosure forms for a long time. If you're buying or selling in Iowa City, our buyers and sellers resources are a good place to start, or you can go straight to Find Your Agent and ask the build-year question in person.
