Radon Map of Wisconsin

This radon map, representing the yearly averages of radon levels in the main floor, is from the Wisconsin Department of Health and Family Services. This map is derived from 87,000 basement test results obtained from companies that sell radon detectors.

The conversion to the main-floor average shown on the map is based on a random survey of 1,100 houses, in which one-year follow-up measurements were done on the first floors in 200 houses where basement 2-day screening levels were over 4 pCi/L (picoCuries per liter). Year-average main-floor radon levels for individual houses were typically 40% of the corresponding basement short-term levels. They ranged from 10% to 100% of the basement short-term results, with the distribution peaking at 40%, the average.

For the radon map, basements with short-term test results over 10 pCi/L were taken to correspond statistically (though not for any particular house) to main-floor year averages higher than the EPA 4 pCi/L guideline. The more radon measurement results there are for a given zip code, the better this estimating procedure is.

Estimated Percentages of Homes with Radon >4pCi/L, Main Floor Year Average

  • Zone 1. Zone 1 – Highest Potential (greater than 20% > 4pCi/L)
  • Zone 2. Zone 2 – Moderate Potential (from 10-20% > 4pCi/L)
  • Zone 3. Zone 3 – Lower Potential (from 1-10% > 4pCi/L)
  • Zone 4. Zone 4 – Low Potential (from 0-1% > 4pCi/L)
  • Zone 5. Zone 5 – Low tested areas (less than 4 measurements)


Radon Test Measurements by County & Zip Code

You can also look at radon test data by county and zip codes within the following south-east Wisconsin counties:

If you are interested in other counties not listed above, we recommend you check the Department of Health & Family Services website.

Radon testing can be performed as part of your home inspection or on its own. Radon gas, an invisible, odorless, radioactive gas created during the natural decay of uranium in the soil, has been shown to cause lung cancer in people who are exposed to elevated levels over a long period of time. Wisconsin has moderate to high concentrations of radon and radon levels vary from house to house and have nothing to do with age, quality or upkeep of the home.