MARSHFIELD, Mo. –If you have made your home more energy efficient, or plan to do so, you might want to test for radon, says a University of Missouri Extension natural resource engineering specialist.

“If you have significantly tightened up your home through weatherization or if you have closed foundation crawl space vents to reduce heat loss, you should test or retest the home for radon,” said Bob Schultheis. “That’s because radon might have been leaking harmlessly outdoors through the cracks and vents that are now sealed up.”

Radon is a naturally occurring radioactive gas found in the soil that can enter buildings through holes and cracks in foundations. Long-term exposure to high levels of radon can greatly increase the risk of lung cancer, especially among people who smoke.

According to the Environmental Protection Agency, radon is the second-leading cause of lung cancer, and the leading cause of lung cancer among nonsmokers. EPA estimates about 21,000 U.S. deaths each year are related to radon exposure, including about 3,000 deaths of people who have never smoked.

“All counties in Missouri have radon and 18 percent of homes in the state have radon levels above the level considered dangerous,” Schultheis said.

The amount of radon in the soil can vary greatly from place to place. A house with dangerously high radon levels might stand next to one with low levels, he said.

Missouri residents can get a free radon test kit from the Missouri Department of Health and Senior Services (see Low-cost kits are also available from hardware stores and home improvement centers. These test kits are typically placed in the lowest lived-in level of the house for two to seven days, then mailed to a lab for analysis. Depending on the lab, you might receive test results by mail or access them online.

While there is no level of radon that is considered absolutely “safe”—even exposure to the low concentrations of radon typically found outdoors carries some small risk—the Environmental Protection Agency has set an “action level” of 4 picocuries per liter of air (“curie” is a unit of measure for radioactivity).

If your house tests at 4 pCi/L or higher, EPA recommends a second, long-term test—three to 12 months—to verify the initial results. EPA also advises homeowners to at least consider taking action if their home tests at 2 pCi/L or higher.

If you decide you need to take action on radon in your house, take the time to carefully evaluate your options, Schultheis said. The dangers of radon come from long-term exposure—years, even decades.

Relative risk is one way for people to assess the danger, he said. For example, the risk of lung cancer with 4 pCi/L of lifetime radon exposure is about five times the risk of dying in a vehicle crash.

Sometimes fixing the problem may be as simple as sealing cracks in the foundation. Schultheis said that was the case for his own house in Webster County, Mo.

Gaps in the foundation slab had appeared because form boards left in place after the concrete was poured had shrunk. “I put mastic in the gaps and the radon problem went away,” he said.

Other inexpensive measures you might take to reduce radon include making sure your sump pit is tightly sealed and caulking joints where the floor slab meets the walls.

In some cases, reducing radon to acceptable levels might involve installing a system that uses a vent pipe and fan to pull radon from under the foundation and vent it through the roof.

For more information:

-“Radon: An Indoor Health Hazard?” (MU Extension guide G1968), available for download at

-Information from the Missouri Department of Health and Senior Services:

-Information from the Environmental Protection Agency: