Wisconsin Radon: Testing, Levels, and Mitigation
Wisconsin sits on some of the most radon-prone ground in the country. Large parts of the state are EPA Radon Zone 1, and about one in 10 homes tests above the level where the EPA recommends action. This guide pulls the whole picture together for Wisconsin homeowners: where radon comes from, how the county map looks, how to test, what your number means, how mitigation works, what it costs, and how the whole thing plays out during a home sale. Badger State Radon is a free service that connects you with independent local radon professionals, so wherever you land in this guide, the next step is a quick match, not a sales pitch from us.
What radon is, and why Wisconsin
Radon is a naturally occurring radioactive gas produced as uranium breaks down in soil and rock. It has no color, odor, or taste, so a home can hold high levels for years without anyone noticing. The gas seeps up through cracks in foundations and floors, gaps around pipes, sump openings, and it can even arrive dissolved in well water. Wisconsin geology makes this a statewide issue rather than a local one. The EPA Map of Radon Zones ranks counties by their predicted average indoor level, and 29 of the 72 counties in Wisconsin fall in Zone 1, the highest category. Every Wisconsin county is EPA Radon Zone 1 or Zone 2. The state has no Zone 3 county.
Radon and your health
The reason any of this matters: radon is responsible for about 21,000 lung cancer deaths a year in the United States and is the leading cause of lung cancer among people who do not smoke, according to the EPA and the U.S. Surgeon General. That is the one health fact worth stating plainly. What you do with it is simple and practical: test your home, and if the level is high, get it fixed. This guide does not offer medical advice, and no one can tell you your personal risk from a single number. Testing and mitigation are the levers you actually control.
Wisconsin radon levels by county
The table below shows the EPA Radon Zone for the areas we cover, from Madison and Dane County across central and western Wisconsin. Zone is a countywide screening designation, not a reading for any single home, which is why testing still matters even in a Zone 1 county. For a deeper breakdown, see our guide to Wisconsin radon levels by county.
| Area (anchor city) | County | Region | EPA Radon Zone |
|---|---|---|---|
| Madison | Dane | south-central Wisconsin | Zone 1 |
| Dane County | Dane | south-central Wisconsin | Zone 1 |
| Eau Claire | Eau Claire | west-central Wisconsin | Zone 2 |
| La Crosse | La Crosse | the western Wisconsin Coulee Region | Zone 2 |
| Wausau | Marathon | north-central Wisconsin | Zone 1 |
| Stevens Point | Portage | central Wisconsin | Zone 1 |
| Janesville | Rock | south-central Wisconsin | Zone 1 |
| Fond du Lac | Fond du Lac | east-central Wisconsin | Zone 1 |
| Appleton | Outagamie | the Fox Valley | Zone 2 |
| Green Bay | Brown | northeastern Wisconsin | Zone 2 |
Zone 1 means the EPA predicts an average indoor level at or above 4 pCi/L; Zone 2 means 2 to 4 pCi/L. Every Wisconsin county is EPA Radon Zone 1 or Zone 2. The state has no Zone 3 county. Zone is a countywide screening designation, not a reading for any one home, so check your address on the WI DHS radon results map and test to learn your level. Sources: EPA Map of Radon Zones and Wisconsin DHS.
Testing your home
There are three common ways to measure radon. A short-term test uses an activated-charcoal kit and runs two to 90 days, most often just a few days, which makes it the fast option during a sale. A long-term test uses an alpha-track detector for more than 90 days and gives a better estimate of your year-round average. A continuous radon monitor logs the level hour by hour. For a real-estate test, the protocol is a minimum 48-hour test under closed-building conditions: windows and outside doors stay shut, with those conditions started at least 12 hours before the test and held throughout, so the result reflects a fair reading. The EPA radon standards of practice spell this out. In Wisconsin, 17 regional Radon Information Centers serve all 72 counties, and a test kit runs about $15 including lab analysis. You can reach them at 1-888-LOW-RADON (1-888-569-7236). Learn more on the radon testing page.
Understanding your result
Results come back in picocuries per liter, written pCi/L. At or above 4.0 pCi/L, the EPA recommends fixing the home. Between 2 to 4 pCi/L, it recommends you consider a fix, since there is no level with zero risk. One high short-term test is a reason to confirm, not to panic: the EPA suggests a follow-up test before you commit to a system. Our guide to radon test results explained walks through what each number means and when a retest makes sense.
How mitigation works
The standard fix in Wisconsin is active sub-slab depressurization. A radon professional runs a suction pipe through the foundation slab and connects it to an inline fan that runs continuously, drawing radon from beneath the home and venting it above the roofline before it enters your living space. The right design depends on the foundation: a poured basement or slab often needs a single suction point, block walls may need wall depressurization, and a crawl space calls for a sealed membrane with suction beneath it. Sealing cracks supports the system but is not a fix on its own. Systems should meet the ANSI and AARST standards, and a manometer on the pipe shows the fan is working. See radon mitigation and crawl space and basement radon for the details, and the EPA Consumer's Guide to Radon Reduction for the national standard.
What it costs
Wisconsin DHS estimates a contractor-installed system typically costs $1,000 to $2,000. Where you land in that range depends on your foundation type, the square footage the system covers, the number of suction points, and how the pipe is routed. After the install, the fan runs around the clock and adds a few dollars a month to the electric bill. Publishing honest ranges is deliberate: it helps you budget and weeds out sticker shock. The full breakdown lives in our Wisconsin radon mitigation cost guide.
Radon during a home sale
Radon shows up most often at the worst time: mid-transaction. It is usually tested during the inspection contingency, and a high result tends to leave days, not weeks, to sort out. Wisconsin sellers complete a Real Estate Condition Report under Wisconsin Statutes chapter 709, which asks about property conditions including radon, and a buyer who does not receive it within 10 days of accepting an offer may rescind. Who pays for a fix is negotiable, and mitigation can often be installed within a few days. For the play-by-play, see radon mitigation at a home sale and the guide to selling a house with high radon in Wisconsin. None of this is legal advice; confirm specifics with your agent or attorney.
Radon in well water
If your home is on a private well, radon can arrive in the water as well as the soil gas. It escapes into the air when you shower, wash clothes, or run the dishwasher, and roughly 10,000 pCi/L in water adds about 1 pCi/L to the air. The highest levels are in the granite formations of northcentral and northwestern Wisconsin. Public water systems are already treated, so this is a private-well question. WI DNR suggests considering treatment when well-water radon tops 4,000 pCi/L. See radon in water and the radon in well water guide, and the Wisconsin DNR page on the topic.
A Wisconsin homeowner radon checklist
- Test your home, ideally in winter, with a short-term kit from a Radon Information Center or a certified professional.
- If the result is at or above 4.0 pCi/L, run a follow-up test to confirm.
- If you are on a private well, test the water separately.
- If levels are high, get matched with an independent local radon professional for a mitigation quote.
- After a system is installed, retest to confirm it worked, then retest every two years and after major renovations.