Radon in Iowa: A Homeowner's Guide

Iowa has the most serious residential radon problem in the country, and it is a problem with a known, reliable fix. The EPA designates the entire state of Iowa as Zone 1, the highest of its three radon zones — there is no low-risk county here. Iowa HHS states that the Iowa Radon Survey found Iowa has the largest percentage of homes above the EPA action level of 4 pCi/L of any state, at 71.6 percent. Radon is invisible, has no odor, and over years of exposure is a leading cause of lung cancer. It is also measurable for very little effort and fixable with well-understood technology. This guide covers why Iowa reads so high, how to test correctly, what your number means, and what mitigation actually involves.

Why is radon so high in Iowa?

Iowa is entirely EPA Radon Zone 1, meaning every county in the state is in the highest-risk category. Iowa HHS explains the designation directly: Zone 1 means at least 50 percent of homes are projected above EPA's recommended action level. Iowa HHS also states that the Iowa Radon Survey indicated Iowa has the largest percentage of homes above the EPA action level of 4 pCi/L — 71.6 percent. We attribute that figure to Iowa HHS rather than asserting it ourselves, because the state publishes it without a data vintage.

The cause is geology. Radon is produced continuously as uranium in soil and rock decays. Iowa's glacial drift and the deep windblown loess that mantles much of the state contain the parent material, and those soils are permeable enough to let the gas migrate. The gas follows the path of least resistance, and in an occupied house that path leads through foundation cracks, control joints, the gap where the slab meets the wall, plumbing and utility penetrations, sump pits, crawlspace floors and block wall cavities.

The practical consequence is that radon here is not a neighborhood problem or an old-house problem. It is a soil problem, and it is house-specific. A 1910 farmhouse and a home finished last year on the same road can produce very different numbers, and neighboring houses routinely do. The only way to know a house's level is to measure that house.

How do you test a house for radon in Iowa?

You have two honest options, and which one you use depends on why you are testing. A short-term test — a charcoal kit or a continuous radon monitor left in place for at least 48 hours under closed-house conditions — gives a fast snapshot and is what nearly every real estate transaction uses, because transactions run on deadlines. A long-term test, left in place for 90 days or more, averages across weeks and gives a truer picture of what you actually live with year-round.

Placement and conditions decide whether the result means anything. Put the device in the lowest level of the home that is used or could reasonably be used as living space, roughly two to six feet off the floor, away from exterior walls, drafts, windows, HVAC registers, sump pits and areas of high humidity. Closed-house conditions mean windows and exterior doors stay shut except for normal entry and exit, starting at least twelve hours before the test and continuing throughout it. Whole-house fans and window air conditioners stay off. Normal furnace and central air operation is fine.

For a transaction, a continuous monitor placed by a professional is worth it: it logs hourly readings, records tampering such as an opened window, and produces a report both sides can trust. For a home you already own, a long-term test is the better information, because it tells you what you actually live with rather than what one week looked like.

What radon level is dangerous, and when should you mitigate?

EPA's action level is 4.0 pCi/L. At or above that number, the recommendation is to fix the home. Iowa HHS points homeowners to that same EPA action level, and given that the state is Zone 1 statewide, a result at or above 4.0 is a common outcome here rather than an unusual one.

Below 4.0 is not the same as safe. There is no threshold below which radon is known to carry no risk, and EPA notes that homeowners may consider fixing between 2 and 4 pCi/L. That is a judgment call and it turns on how you use the house. A finished basement bedroom where a child sleeps every night is a different exposure than an unfinished basement nobody enters. Smoking in the home multiplies radon risk substantially, which is worth weighing in the decision.

One result is not a verdict. Radon varies day to day with weather, barometric pressure and how the house is being operated, and it varies seasonally. If a short-term test lands close to the action level, the right response is usually a second test or a long-term test rather than either panic or dismissal. If it lands well above, mitigation is the answer and there is little reason to keep measuring first. If a seller offers an old test result, treat it as history — levels change with foundation work, new windows, added insulation, HVAC changes and settling.

Does winter change Iowa radon readings?

Yes, and usually upward. Iowa's heating season tends to produce the highest readings of the year for two reasons that compound each other. First, the house is closed and the furnace is running, which drives the stack effect: warm air rises and leaks out the upper part of the house, the house pulls makeup air in from below, and that slight negative pressure at the foundation actively draws soil gas indoors. Second, frozen and snow-covered ground around the foundation caps the soil surface, so radon that would otherwise vent harmlessly to open air is steered toward the warmer, lower-pressure space under your slab.

That seasonality has a practical consequence for testing. A short-term test run in July with the house open can substantially understate winter exposure. It is still a valid test if closed-house conditions were held, and it is often the only option a transaction timeline allows — but a summer result near the action level deserves a follow-up during the heating season.

Iowa also has strong wind and pressure swings, and a continuous monitor will show readings moving with a passing front. That is normal and it is exactly why a single grab sample is not how radon is measured. If you own the home and want a real answer, run a long-term test through a winter.

What does radon mitigation involve?

The standard fix is active sub-slab depressurization. A contractor cores a hole through the basement slab, excavates a suction pit in the aggregate beneath it, runs a sealed pipe from that pit up through the house or along the exterior, and installs an inline fan that runs continuously and discharges above the roofline. The fan holds the space under the slab at slightly lower pressure than the house, so soil gas is pulled out and vented rather than drawn in. Sealing cracks, sump covers and other openings supports the system but does not replace it — sealing alone is not a reliable fix.

Crawlspaces are handled differently, usually with a sealed membrane over the soil and suction drawn from beneath it. Homes with multiple foundation types, additions on separate slabs, or block walls acting as a radon pathway may need more than one suction point. A working system includes a manometer or other monitor you can read at a glance to confirm the fan is still running.

Always re-test after installation. A system that was not verified is a pipe, not a solution. Retest again every couple of years and after any significant change to the foundation, HVAC or building envelope. Keep the installation paperwork and every test result on file — Iowa buyers ask about radon, and documentation that shows a measured problem and a measured fix is worth having when you sell.

Radon FAQs for Iowa homeowners

Is Iowa really Zone 1 everywhere? Yes. Iowa HHS states that EPA designates the entire state as a Zone 1 state. There is no Iowa county exempt from the recommendation to test.

Does a new home need testing? Yes. Radon comes from the soil, not from the age of the house. Some newer Iowa homes are built with a passive radon-resistant rough-in — gas-permeable fill, a sealed membrane and a capped vent pipe. That pipe makes a future fix simpler; it does not guarantee a low number, because passive venting relies on natural air movement that is weakest exactly when radon is highest. Test the house.

Can radon come in through well water? It can. Radon dissolves in groundwater and is released into the air when water is agitated by showers, dishwashers and laundry. Waterborne radon is usually a smaller contributor than soil gas, but on a private well it is worth ruling out if an air test comes back high and the source is not obvious. It takes a separate water test.

Does an open basement window fix it? No. It changes the reading while the window is open and invalidates a test in progress. It does not address the pressure difference pulling gas in.

Who should I hire? Use a radon measurement or mitigation professional who holds a current national certification and can show you their credential and their proposed system design.