Radon

Radon is a radioactive gas that comes from the natural breakdown of uranium in soil and rock. It seeps into homes through cracks and openings in the foundation, and you can’t see, smell or taste it. Radon is the leading cause of lung cancer among people who have never smoked. The only way to know your level is to test, and high levels can be fixed.

• Homeowners
• Renters
• Home buyers

Why radon matters

• EPA estimates radon causes about 21,000 lung cancer deaths in the U.S. each year.
• Radon is the second leading cause of lung cancer overall, after smoking.
• For smokers, radon and smoking together greatly increase the risk.
• Nearly 1 in 15 U.S. homes is estimated to have radon at or above EPA’s action level.

Any home can have high radon: new or old, drafty or tight, with or without a basement. Two houses next door to each other can have very different levels.

How radon gets in

• Cracks in basement floors and walls
• Gaps around pipes, wires and sump pits
• Construction joints and gaps in suspended floors
• Crawl spaces with dirt floors
• Well water, in some areas

Homes tend to pull air up from the soil, especially in winter when warm air rises and escapes through the top of the house. That’s why radon levels are often highest in the lowest lived-in level and in colder months.

What the numbers mean

Radon is measured in picocuries per liter of air (pCi/L).

There’s no known safe level of radon. Lower is always better.

How to test

• Short-term tests (2 to 90 days) give a quick answer. Most are small charcoal canisters or devices you leave out and then mail to a lab.
• Long-term tests (more than 90 days) give a better picture of your year-round average.
• Continuous digital monitors show readings over time. Choose one that has been tested for accuracy.

Tips for an accurate test

• Test in the lowest level of the home that is used regularly (a finished basement or the first floor)
• Keep windows and outside doors closed for 12 hours before and during a short-term test, except for normal coming and going
• Place the test at least 20 inches off the floor, away from drafts, kitchens, bathrooms, exterior walls and heat
• Don’t move or disturb the test while it’s running
• Follow the kit’s instructions, and mail it to the lab right away

Low-cost test kits are sold at hardware stores and online, and many state radon programs offer free or discounted kits. You can also hire a certified radon measurement professional.

If your level is high

Radon problems can be fixed. The most common method is active soil depressurization (also called sub-slab suction):

• A pipe is installed through the basement floor or crawl space liner.
• A fan pulls radon from under the house and vents it above the roof.
• Cracks and openings are sealed to make the system work better.
• A gauge (manometer) on the pipe shows the system is running.

Systems can usually cut radon levels by up to 99%. The cost is often about the same as other common home repairs. Retest after the system is installed, and every two years after that.

Hiring a radon contractor

• Hire a contractor certified by a national radon proficiency program (such as NRPP or NRSB) or licensed by your state, if your state requires it.
• Get more than one estimate and a written contract.
• Ask about a warranty and how the system will be tested after installation.

Buying, selling or building a home

• Buying: ask for a radon test as part of your home inspection, and get the results before closing.
• Selling: some states require you to disclose known radon test results.
• Building: ask your builder for radon-resistant construction: a gas-permeable layer under the slab, a vapor barrier, sealed openings and a vent pipe. It’s much cheaper to install during construction, and the fan can be added later if needed.

Renters

You can test your apartment or rental home yourself. If your level is high, give the results to your landlord in writing and ask them to fix it. Some states and cities have rules about radon in rental housing.

Radon in well water

If you have a private well in an area with high radon, radon can come out of the water when you shower or wash dishes. Test your water if your air radon is high or your state recommends it. Treatment systems are available.

Radon at work

Workers in basements, tunnels, mines, utility vaults and some buildings can also be exposed. Radon mitigation contractors and others who work with radon should follow worker protection rules and their certification program’s safety practices.

Last updated: October 1, 2026