Radon Testing: When, How, and What the Numbers Mean

Radon is a radioactive gas that comes up from the soil. You can't see it, smell it or taste it, and it can build up inside a house, especially in the basement and lower floors. The EPA says radon is the second leading cause of lung cancer in the U.S. after smoking, and the leading cause among people who don't smoke.

The good news: testing is cheap and easy, and high levels can be fixed.

01How radon gets in

Radon forms naturally when uranium in soil and rock breaks down. It moves up through the ground and into a house through:

• Cracks in floors and walls
• Gaps around pipes and wires
• Construction joints where the floor meets the wall
• Sump pits and floor drains
• Crawlspaces

Any home can have high radon: new or old, drafty or tight, with or without a basement. Levels can be very different even between neighboring houses, so the only way to know is to test.

02The numbers

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

• 4 pCi/L or higher: the EPA recommends fixing your home.
• Between 2 and 4 pCi/L: the EPA says to consider fixing it.
• Below 2: lower risk, but no level of radon is completely safe.

03When to test

• Any time, if you've never tested.
• When you're buying a house. Many buyers add a radon test to the home inspection.
• After renovations, especially if you finish a basement or change the heating system.
• Every couple of years, or after major changes to the house.

Winter is a good time, since houses are closed up, but you can test year-round.

04How to test it yourself

1. Buy a test kit. Hardware stores and many state radon programs sell them, and some states offer them free or at low cost.
2. Pick the spot: the lowest level of the house that's lived in (a finished basement, or the first floor if the basement isn't used). Not in a kitchen, bathroom, laundry room or crawlspace.
3. Close up the house: keep windows and outside doors closed for at least 12 hours before and during a short-term test, except for normal coming and going.
4. Place the kit about 20 inches or more off the floor, away from drafts, exterior walls and heat sources.
5. Leave it for the time on the package (usually 2 to 7 days for a short-term test).
6. Mail it to the lab right away, following the instructions.

Short-term tests (2 to 90 days) give a quick snapshot. Long-term tests (more than 90 days) give a better picture of the yearly average. If a short-term test comes back high, the EPA suggests a second test to confirm before you fix it.

Continuous electronic radon monitors are another option; they show levels in real time.

05When you're buying or selling

In a real estate deal, a short-term test is common. The EPA's guidance for home buyers and sellers covers test placement and timing. A certified radon tester can run the test so it holds up in negotiations.

06Fixing high radon

The most common fix is sub-slab depressurization: a pipe through the basement floor and a fan that pulls radon from under the house and vents it above the roof. It's a proven, widely used system. Sealing cracks helps but usually isn't enough on its own.

Hire a contractor certified by your state or a national radon certification program. After the system is installed, test again to make sure it worked.

07Learn more

Your state radon program has local information, and the EPA's "A Citizen's Guide to Radon" is the standard plain-English guide.

Add a radon test to your list along with checking your smoke and CO alarms.

Sources (2)

U.S. EPA: A Citizen's Guide to Radon; U.S. EPA: Radon.

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