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

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