Weather, Seasons, and Radon Levels in Milwaukee, WI Homes

Radon levels indoors can change with outdoor weather, indoor heating habits, air pressure, wind, and the way a home exchanges air with the soil beneath it. In Milwaukee, WI, the effect is often most noticeable during the heating season, when homes are closed up and warm indoor air creates pressure differences that can draw soil gases indoors.

Weather does not create radon, but it can change how much enters a building and how long it remains there. Because radon is invisible and odorless, testing is the only dependable way to know the level inside a particular home.

Why can radon levels rise during cold weather?

Cold weather often increases indoor radon readings because homes are more tightly closed and heated. Warm air naturally rises through a house and exits through small openings in the upper portions of the building. This can create lower air pressure near the foundation, sometimes called the stack effect.

When indoor pressure is lower than the pressure in the soil, soil gas can be pulled through openings such as:

• Cracks in concrete floors or foundation walls
• Gaps around plumbing, wiring, sump pits, or floor drains
• Joints between floors and foundation walls
• Porous masonry or unfinished block walls
• Crawl spaces and exposed soil

During a Milwaukee winter, windows and exterior doors generally remain closed for long periods. Furnaces and other heating systems operate regularly, and basements may be connected to upper living areas through stairways, utility openings, or gaps around ductwork. These conditions can increase the movement of soil gas into the home.

That does not mean every winter test will be higher than a summer test. Radon varies from house to house and from day to day. Winter simply tends to provide more consistent closed-building conditions and more opportunities for pressure-driven entry.

How do storms and barometric pressure affect radon?

A rapid drop in outdoor barometric pressure can temporarily increase radon movement from the soil into a building. Storm systems may also change wind direction, temperature, humidity, and soil moisture at the same time.

The pressure difference between the soil, the building, and the outdoor air can shift quickly during severe weather. As a result, radon readings may become more variable. A short-term test conducted during unusually stormy or windy conditions may not represent the home’s typical average level.

This does not make the test automatically useless. It does mean the result should be interpreted in light of the testing conditions. If a reading is unexpectedly high or differs sharply from earlier results, a follow-up test may help determine whether the result reflects a temporary weather pattern or a persistent indoor condition.

Does wind increase indoor radon?

Strong wind can affect radon levels by changing air pressure around the home. Wind moving across a roof, wall, chimney, or foundation can create areas of higher and lower pressure. Those changes may increase air movement through cracks and openings in the building envelope.

Wind can also make radon concentrations fluctuate rather than simply rise. In some homes, increased ventilation may lower the concentration temporarily. In others, wind-driven pressure differences may pull more soil gas indoors.

For that reason, unusually high winds are not ideal conditions for a two- or three-day test. A test performed during normal weather is generally easier to interpret. Long-term testing is less affected by any single windy day because the result averages conditions over a much longer period.

Why are radon readings sometimes higher in the basement?

Radon usually enters from the soil beneath or alongside a building, so the lowest occupied level commonly has the highest concentration. In homes with basements, the basement floor and foundation walls provide the closest pathways between indoor air and the surrounding soil.

A finished basement is not necessarily protected. Flooring, wall coverings, carpeting, and finished ceilings may hide cracks or openings without stopping soil gas from entering. If the basement is used as a bedroom, office, playroom, or family room, testing should be performed in the lowest level that is regularly occupied.

Homes without basements can also have elevated radon. Entry may occur through slab foundations, crawl spaces, attached garages, or foundation penetrations. Construction age, appearance, and renovation history cannot reliably predict the indoor level.

Does rain affect radon levels?

Rain may influence radon indirectly by changing soil moisture and air movement. Wet soil can alter the pathways through which soil gas travels. Heavy rain may also raise the water level around a foundation or change pressure beneath a slab.

The effect is not predictable in every home. Some houses may show a temporary increase after major rainfall, while others may show little change or even a decrease. Rain is one factor among many, including wind, temperature, barometric pressure, ventilation, and building operation.

A leaking foundation or wet basement should be addressed for moisture reasons, but drying the space alone does not remove the need for radon testing.

Is winter the best time to test for radon?

Winter is often a practical time to conduct a short-term test because closed-building conditions are easier to maintain. Windows and exterior doors are usually kept closed, and normal heating systems can continue operating.
Before and during a short-term test:

• Keep windows and exterior doors closed as much as practical.
• Continue normal heating or cooling operation.
• Avoid placing the device near drafts, direct sunlight, high heat, or excessive humidity.
• Do not move or cover the testing device.
• Postpone testing during unusually severe storms or very high winds when possible.

A short-term test generally lasts from two to 90 days, depending on the device and purpose. A long-term test lasts more than 90 days and can provide a better picture of the home’s average exposure across changing weather conditions.
If a test shows a result at or above 4 picocuries per liter, the U.S. Environmental Protection Agency action level, the result deserves follow-up and consideration of radon reduction measures. Results below that level are not considered risk-free, so a lower reading should not be treated as a permanent guarantee.

Can weather explain a high radon result?

Weather can contribute to a high reading, but it should not be used to dismiss one. A high result may reflect normal seasonal conditions, a temporary pressure change, or a persistent entry problem.
The most useful response depends on the test type, the result, the weather during testing, and whether the home has previously shown elevated levels. When results are near or above the action level, repeat testing or longer-term testing can help clarify the home’s typical condition. If a mitigation system is already installed, unusually high readings may indicate a system problem, a change in building conditions, or a need for further evaluation.
Testing at different times of year can also reveal patterns. For example, a home may show higher readings during cold, closed-up months and lower readings during mild weather when more outdoor air enters naturally. That seasonal difference still matters because residents may spend substantial time indoors during the heating season.

What should Milwaukee households remember?

Weather affects radon mainly by changing air pressure, soil conditions, ventilation, and the way a home operates. Cold weather and closed windows can increase entry and concentration, while storms and strong winds can make short-term readings more variable.

A single reading is useful, but it is a snapshot. Testing under proper conditions, considering the season and weather, and repeating an unexpected result provides a more reliable understanding of indoor radon exposure.