Radon: The Silent Risk Hiding in Basements and Crawl Spaces

Radon is a radioactive gas that comes from the natural decay of uranium in soil. It seeps into homes through foundation cracks, sump pumps, and crawl spaces. You can't see it, smell it, or taste it — and according to the EPA, it causes about 21,000 lung cancer deaths in the U.S. every year.

The action level

The EPA recommends action at 4 picocuries per liter (pCi/L). The World Health Organization sets its threshold lower, at about 2.7 pCi/L. There's no truly safe level — risk rises with both concentration and time exposed.

Where radon is highest

Radon levels vary by geology, not by climate. The Upper Midwest, Appalachia, and parts of the Mountain West tend to have the highest readings. But high results have been found in every state and every type of home — old, new, slab, basement. Your neighbor's result tells you nothing about yours.

How to test

• Short-term tests (2 to 7 days) give you a fast baseline — best for first-time screening

• Long-term tests (90+ days) give you a more accurate annual average

• Continuous radon monitors plug in and give ongoing readings — best if you've already mitigated

If your level is high

Radon mitigation is well-understood and usually costs $800 to $2,500. A licensed contractor installs a sub-slab depressurization system that vents radon to the outside before it enters your living space. Most systems reduce indoor radon by 50 to 99 percent. Re-test 30 days after installation, then every two years.