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