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St. Louis Radon Testing Considerations

There are outside circumstances that can have an effect on radon measurement. These unique situations can become more of a concern for borderline, time sensitive measurements. If you have questions about your radon measurement, please discuss your test results with a certified professional.

Testing Concerns

  • Homes with more than one lower level type should test on each lowest level directly above ground (i.e. basement, & room directly over crawl space & room addition(s) directly on ground)
  • Radon will likely be highest in the lowest level, decreasing as much as 50% on subsequent floors
  • Radon concentration is highest in areas that are close to, or surrounded by, the ground.
  • A vacant home will measure similar to an occupied home, assuming normal temperatures are maintained
  • Radon concentration will vary within the home, but not much on the same level
  • Room to room measurements in large buildings may vary considerably
  • Charcoal testing can sometimes have a bias toward the latter part of the testing period

It is important to remember that Radon continuously fluctuates.

Wind, Rain and other Natural Forces

  • Light rain has little effect on radon concentration
  • Extended rain can block soil pathways and either raise or reduce indoor radon levels
  • Indoor concentrations may be higher during rainy seasons
  • Indoor radon concentration may be higher in the winter months, while the heating system is pulling air up and out of the home via natural heat convection, -"the stack effect".
  • Frozen ground can cap the homes surrounding soil and elevate radon levels
  • Daily radon variation is greater in the summer than the winter
  • High winds can either raise or lower radon levels, depending if the wind creates a positive pressure interior or a negative interior pressure.
  • Low barometric pressure can force soil gases and radon into a home
  • An activated sump pump could pump out radon with the water
  • Radon is usually higher at night and lower during the day

Outside of a real estate transaction and where the measurement was taken in a level not regularly occupied, occupants may also consider testing upper levels and/or areas occupied most frequently. This is not to suggest complacency, there is no known safe level of radon and even low levels present some risk.

Homes, outside of a real estate transaction, with moderate to low levels may consider measuring a second time with either a short term or a long term test.

Most short term tests provide the same mitigation decision as a long term test


The first step to help ensure the safety of you and your family’s health and safety is to have your home tested for radon. At St. Louis Radon, our professional testers deploy the latest in computerized electronic real-time radon monitoring technology to provide you with a comprehensive report, including a complete visual graph of radon level data points as recorded over a 48-hour sampling period.

Learn More About Testing


If testing indicates levels of radon that require action, our team of engineers and technicians will design and install a custom radon mitigation system to safely and effectively redirect radon and other soil gasses out of your home. We also take additional measures to seal and close other possible breaches in the foundation that could let soil gasses into the through cracks or drain tiles systems.

Learn More About Mitigation

New Construction

With new home construction projects, it is crucial to determine the level of radon that may be present in the soil before the home is built. It’s also critical to have the new home retested for potential radon concentrations immediately following occupancy. We also highly recommend installing an Active Dampness Control System (ADC) with every new build.

Learn More About New Construction