Radon Mitigation in Milwaukee, WI: What Wisconsin Homeowners Need to Know

Wisconsin's Radon Profile

Wisconsin has a split radon profile by geography. The northern part of the state — on Precambrian granite and crystalline bedrock with high uranium content — has elevated radon in a more rural context. Southeastern Wisconsin, including Milwaukee, sits on Silurian dolomite and Ordovician limestone overlaid by glacial materials from multiple ice sheet advances.

The glacial till and outwash in Milwaukee County is generally permeable, allowing radon to migrate efficiently from the bedrock below to homes above. Milwaukee County and surrounding counties (Waukesha, Ozaukee, Washington) show consistent elevation above the national average.

Milwaukee's Housing Characteristics

Milwaukee has a diverse housing stock with significant pre-1960 inventory, particularly in city neighborhoods and close-in suburbs like Wauwatosa, West Allis, and Shorewood. Key considerations:

• Block foundations: Common in post-war construction; hollow block cores require specific mitigation approaches
• Basement garages: Milwaukee's cold climate makes attached basement garages common; the garage-basement connection is a radon pathway that should be sealed
• Older sump systems: Many older Milwaukee homes have open sump pits — seal them as part of mitigation
• Newer construction: Suburbs like Brookfield, New Berlin, and Menomonee Falls have more modern construction with potentially better sub-slab conditions

Winter Radon in Milwaukee

Milwaukee winters are severe and long. Buildings are sealed for 5–6 months, eliminating natural ventilation. The stack effect in Milwaukee's older multi-story homes is pronounced — warm air rising through the structure creates significant negative pressure at the basement level, pulling in soil gas.

Testing in January–March typically yields the highest readings of the year. If you test in summer and get borderline results (3–4 pCi/L), consider running a long-term test that captures the winter period before concluding no action is needed.

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