Wisconsin has significant radon risk across much of the state, with an estimated 30–40% of Wisconsin homes testing above the EPA action level of 4.0 pCi/L. The Wisconsin Department of Health Services estimates that radon may be responsible for over 600 lung cancer deaths in Wisconsin annually. Wisconsin’s geology — including granitic bedrock in the northern shield area, glacial till across the state, and limestone formations in the southwestern driftless area — creates varied but often significant radon potential.
EPA Radon Zone Designation
Wisconsin is predominantly EPA Radon Zone 1. Most Wisconsin counties are Zone 1 or Zone 2. The highest-radon areas tend to be in the northern Wisconsin shield counties where granitic bedrock is close to the surface, and in the central sand plain counties where glacial outwash creates radon transport pathways. Southern Wisconsin counties overlying carbonate rock also show elevated levels.
Radon Contractor Licensing in Wisconsin
Wisconsin requires radon contractors to hold current NRPP or NRSB national certification to perform radon measurement and mitigation services. Wisconsin’s radon program is administered through the Wisconsin Department of Health Services. Wisconsin does not have a separate state-specific radon contractor licensing statute — national certification is the operative requirement. The WDHS maintains resources and information on certified professionals. Verify contractor credentials at nrpp.info or nrsb.org before hiring.
Radon Disclosure Requirements in Wisconsin
Wisconsin’s real estate disclosure law requires sellers to complete a Real Estate Condition Report disclosing known defects and conditions. The Wisconsin Real Estate Condition Report includes questions about environmental conditions including whether the property has been tested for radon and the results of any such tests, and whether a radon mitigation system is present. Sellers with knowledge of radon test results must disclose them. Radon testing is common in Wisconsin real estate transactions, particularly in high-radon areas.
Radon-Resistant New Construction (RRNC) in Wisconsin
Wisconsin does not have a statewide RRNC mandate for new residential construction. The Wisconsin Uniform Dwelling Code does not require RRNC features statewide. However, Wisconsin DHS recommends RRNC for new construction in Zone 1 areas. The IRC Appendix F provisions are available for local adoption. Some Wisconsin municipalities have incorporated RRNC requirements. Buyers of new Wisconsin construction should ask builders about RRNC inclusion.
Highest-Radon Counties and Areas in Wisconsin
Wisconsin’s highest-radon areas include the northern shield counties where granitic bedrock is prevalent: Iron, Ashland, Bayfield, Douglas, and Vilas counties. The glaciated central Wisconsin sand plain counties (Adams, Portage, Waushara, Waupaca, Marathon) also show elevated levels. The Milwaukee metropolitan area (Milwaukee, Waukesha, Ozaukee, Washington counties) spans the transition between Zone 1 and Zone 2 areas. The Wisconsin DHS publishes county-level radon data from testing surveys.
Testing Resources for Wisconsin Residents
The Wisconsin Department of Health Services administers the state radon program and provides resources for homeowners including lists of certified contractors, low-cost or free test kit programs (availability varies by year and funding), and technical guidance on radon mitigation. Contact the state radon program directly for the most current contractor list, any available test kit distribution programs, and jurisdiction-specific requirements that may have changed since this page was last updated.
Frequently Asked Questions
Does Wisconsin require radon disclosure when selling a home?
Yes. The Wisconsin Real Estate Condition Report requires sellers to disclose known radon test results and the presence of any radon mitigation system. Sellers with knowledge of elevated radon must disclose it.
What parts of Wisconsin have the highest radon?
Northern Wisconsin shield counties — Iron, Ashland, Bayfield, Douglas, Vilas — have the highest radon potential due to granitic bedrock. Central Wisconsin sand plain counties and parts of southern Wisconsin with carbonate geology also show elevated levels.
Does Wisconsin require radon contractor certification?
NRPP or NRSB national certification is required for radon professionals in Wisconsin. No separate state licensing statute exists. Verify credentials at nrpp.info or nrsb.org before hiring.
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