What your radon test result means

Your radon result comes back as a number in pCi/L. Here is what that number means and what to do if it is high.

What is pCi/L?

Radon is measured in picocuries per liter (pCi/L). It tells you how much radon gas is in the air. A picocurie is a tiny amount of radioactivity, and "per liter" means per liter of the air that was tested.

The average home in the U.S. has about 1.3 pCi/L of radon inside. Outdoor air is usually around 0.4 pCi/L.

When does EPA say to fix it?

The U.S. Environmental Protection Agency recommends fixing your home if radon is 4.0 pCi/L or higher. EPA says there is no known safe level of radon exposure, so it also recommends thinking about a fix between 2.0 and 4.0 pCi/L.

Illinois rules for radon work

32 Ill. Adm. Code Part 422 holds the Illinois rules for radon testing and mitigation work. Section 422.130 covers how to measure, Section 422.140 covers the test devices, and Section 422.150 sets the standard for systems in homes that are already built. Anyone who offers radon testing or mitigation in Illinois needs the license for that work.

What if your number is high?

It depends on why you tested. For a homeowner's first test outside a sale, Illinois Appendix A lays out a follow-up test after a high short-term result. For a proper home-sale test, Appendix B says to fix the home at 4.0 pCi/L or higher. If the test rules were not followed or two results do not agree, talk with an Illinois-licensed measurement professional before you count on the number.

If you need a system, an Illinois-licensed mitigator looks at your foundation, the layout, and your test results, and designs a system for your home. A fan system that pulls radon from under the floor is common, but the design may also need to handle drain tile, a crawlspace, or block walls.

Illinois requires a test after the system goes in. The test can start no sooner than 24 hours after the system is running, and no later than 30 days after it is finished and turned on. The system runs normally the whole time. You can run that test yourself, or an independent Illinois-licensed measurement professional can do it. Illinois also recommends a new test at least every two years and after big changes to the building.