The Invisible Gas in Your Home

What Radon Is and Where It Comes From

Radon is a naturally occurring noble gas in the uranium decay chain. It's produced wherever uranium-containing rock and soil exist — which is practically everywhere, though concentrations vary enormously by geography. Granite-rich areas, the Midwest, and parts of the Mountain West tend to have the highest levels, but elevated radon has been found in homes in all 50 states.

Because radon is a gas, it migrates upward through soil and enters homes through:

• Cracks in foundations and concrete floors
• Gaps around pipes and cables entering the building
• Sump pits and floor drains
• Crawl spaces and porous construction materials

Once inside, radon can accumulate — especially in basements and ground-floor rooms with limited ventilation. When radon decays, it produces radioactive particles called radon progeny (polonium-218, lead-214, bismuth-214, polonium-214) that you inhale. These particles lodge in lung tissue and emit alpha radiation that damages DNA directly.

How Much Is Too Much?

The US EPA sets an action level of 4 picocuries per liter (pCi/L) — above this, remediation is recommended. The EPA also suggests considering action above 2 pCi/L. The average indoor level in US homes is about 1.3 pCi/L; outdoor air averages around 0.4 pCi/L. In Europe, the World Health Organization action level is 100 Bq/m³ (approximately 2.7 pCi/L).

There is no known safe threshold — the risk appears to be linear with no lower bound, meaning even modest elevations carry some increased risk [2]. But the practical risk jumps significantly above 4 pCi/L, where the EPA estimates that lifetime exposure increases lung cancer risk by about 7 per 1,000 people for non-smokers, and by 62 per 1,000 for smokers.

The Smoking-Radon Combination Is Particularly Dangerous

Radon and cigarette smoke don't just add — they multiply. Data from European pooling studies found that heavy smokers exposed to radon levels above 200 Bq/m³ had an odds ratio of 29.3 for lung cancer compared to non-smoking, low-radon households [2]. The two carcinogens amplify each other's damage to lung tissue. This means smokers living with elevated radon have an especially urgent reason to both quit and test their home.

How to Test Your Home

Testing is easy, affordable, and the only way to know your radon level:

Short-term tests (2–90 days): Charcoal canisters or alpha track detectors placed in the lowest livable area. Available at hardware stores for $15–30. Results come back by mail in 1–2 weeks.

Long-term tests (90+ days): Alpha track detectors give a better average that accounts for seasonal variation. More accurate than short-term tests for determining actual exposure.

Testing tips:

• Test the lowest level you regularly use (basement if you use it, ground floor if not)
• Close windows and doors 12 hours before and during a short-term test
• Don't test during unusually stormy weather
• Retest after any major renovation or sealing of the home

Reducing Radon Levels

If your home tests above 4 pCi/L, professional mitigation is highly effective:

Sub-slab depressurization (the gold standard): A pipe is drilled through the foundation and connected to a fan that draws radon from beneath the slab and vents it outside. Reduces levels by 50–99% in most homes. Cost: $800–2,500 depending on foundation type.

Crawl space mitigation: A sealed cover over the crawl space with a vent pipe and fan. Very effective for homes on crawlspaces.

Ventilation improvements: Heat recovery ventilators (HRVs) and improved basement ventilation can reduce levels modestly. Less reliable than active depressurization but helpful as a supplemental measure.

For new construction, radon-resistant techniques (passive pipes, sealed membranes) can be installed at low cost and make active mitigation easier if levels are still elevated.