Radon, Explained

Radon is the second-leading cause of lung cancer overall, and the #1 cause among people who have never smoked. The EPA estimates it causes about 21,000 lung cancer deaths in the US every year, more than drunk driving. When radon gas decays, it releases tiny radioactive particles that lodge in lung tissue and damage it over years of exposure.

The US Surgeon General and the EPA recommend that every home below the third floor be tested for radon. There is no known safe level of radon exposure, the goal is simply to get your home as low as reasonably possible.

Your house acts like a slow vacuum. Warm air rising through the building pulls soil gas up through every available opening: cracks in the slab or foundation walls, the gap around sump pits, crawlspace floors, utility penetrations, even well water. This "stack effect" is strongest in basements and lowest levels, which is why radon concentrates there.

It doesn't matter whether a home is old or new, drafty or tight, with or without a basement. Two houses next door to each other can have wildly different levels, because it all depends on the soil, the foundation, and the pressure dynamics under that particular home.

Testing is cheap and easy. You can hire a radon measurement professional for a precise 48-hour continuous-monitor test, standard in real-estate transactions, or start with a DIY kit from a hardware store or your state radon program. Short-term tests run 2–7 days; long-term tests (90+ days) capture seasonal swings and give the truest picture of annual exposure.

If a short-term result comes back at 4.0 pCi/L or higher, confirm with a follow-up test or move straight to mitigation. Retest every two years even after a good result, and after any major renovation, foundation work, or new HVAC system.

The standard fix, active sub-slab depressurization, is refreshingly effective. A certified mitigation contractor seals a pipe into the foundation, and a quiet inline fan pulls radon-laden soil gas from beneath the slab and vents it above the roofline, before it can enter your home. Most systems install in a single day, cost $800–$2,500, reduce levels by up to 99%, and run on about as much electricity as a light bulb.

Building a new home? Ask about radon-resistant new construction (RRNC), the passive piping costs a few hundred dollars at build time and can be activated with a fan later if needed.