Radon test results explained

Radon is a radioactive gas that comes from the natural breakdown of uranium in soil, rock and water [1]. You can't see, smell or taste it, and the U.S. Environmental Protection Agency (EPA) says any home may have a radon problem [1]. The only way to know a home's level is to test.

A radon report can look confusing the first time you see one. This guide explains the numbers and what to do about them. It's based mainly on two EPA guides: A Citizen's Guide to Radon and the Home Buyer's and Seller's Guide to Radon.

Why it matters

Radon is a health concern because breathing it over time raises the risk of lung cancer. The EPA estimates that about 21,000 lung cancer deaths a year in the U.S. are related to radon [1].

What pCi/L means

Radon results in the U.S. are usually reported in picocuries per liter of air (pCi/L). A picocurie is a tiny unit of radioactivity, so pCi/L tells you how much radiation from radon is in each liter of air. Some reports use other units. The EPA's action level of 4 pCi/L is the same as 150 becquerels per cubic meter (Bq/m³), a metric unit you may see on some reports [3].

For comparison, the EPA estimates the average indoor radon level in U.S. homes is about 1.3 pCi/L, and outdoor air normally has about 0.4 pCi/L [1].

The 2.0 and 4.0 levels

Result	What the EPA says
4.0 pCi/L or higher	Fix the home [1, 2]
2.0 to 3.9 pCi/L	Consider fixing the home [1, 2]
Below 2.0 pCi/L	No EPA action, though the EPA notes that levels below 4 pCi/L still carry some risk [1]

The 4.0 level is the EPA's action level, not a line between safe and unsafe. The EPA says levels below 4 pCi/L still pose some risk, and that radon levels in many homes can be brought down to 2 pCi/L or less [2].

Short-term vs long-term tests

There are two kinds of tests [2]:

Short-term tests stay in the home for 2 to 90 days, depending on the device. Tests done during a home sale are usually short-term.
Long-term tests stay in the home for more than 90 days.

Radon levels tend to change from day to day and season to season. That's why the EPA says a long-term test is more likely to show a home's year-round average than a short-term test [1].

For a home you already live in, the EPA recommends [1]:

Start with a short-term test.
If the result is 4 pCi/L or higher, follow up with either a long-term test or a second short-term test. Use a second short-term test if you need results quickly.
Fix the home if the long-term result is 4 pCi/L or more, or if the average of the two short-term tests is 4 pCi/L or more.

Tests should be placed in the lowest lived-in level of the home, and not in a kitchen or bathroom [1].

Why results can differ

Two tests on the same house can give different numbers. Common reasons:

Season and weather. Levels vary from day to day and season to season [1].
Where the test sat. The EPA says to test in the lowest level of the home that could be used regularly, finished or not [2]. A test in a basement and a test on the main floor may not match.
House conditions. For tests shorter than four days, windows and outside doors should be closed for at least 12 hours before the test starts and kept closed during it [2].

Your neighbor's result won't tell you yours. The EPA says you can't predict a home's radon level from state, local or neighborhood measurements, and homes next to each other can have very different levels [2]. Every home needs its own test.

Reading a real estate radon result

During a home sale there's usually no time for a long-term test. The EPA's buyer and seller guide gives three short-term options, each at least 48 hours long [2]:

Option	How it works	When to fix
Two tests at the same time	Two short-term tests side by side in the same spot	If the average of the two is 4 pCi/L or more
Two tests back to back	A second identical test in the same spot, started right after the first ends	If the average of the two is 4 pCi/L or more
Continuous monitor	An electronic monitor that records levels over the test period	If the average level is 4 pCi/L or more

Whichever option is used, the number the EPA's guidance looks at is the average, not the single highest reading.

What to do with a high result when buying

A high result is usually fixable. The EPA says most homes can be fixed for about the same cost as other common home repairs [2]. Here's how it usually goes:

Talk about it in the contract. The EPA says buyers and sellers should discuss timing and costs, and that a contract can spell out when radon reduction will be done and who will pay for it [2]. Your real estate agent can help with the wording.
Use a qualified radon professional. Mitigation is usually done with a vent pipe and fan that pull radon from under the house and vent it outside. The details depend on the foundation.
Retest after the work. The EPA says to test again after the mitigation system is installed, to confirm it lowered the level [2].
Check an existing system. If the house already has a radon system, ask the seller for past test results and test again. One finding that can show up on a report is a radon vent pipe that ends below the roofline.

State radon resources

Radon programs are run by states, and what they offer changes over time.

North Carolina: The North Carolina Radon Program, part of NCDHHS, recommends that every home be tested and links to lists of certified radon measurement and mitigation professionals [4].
Georgia: The University of Georgia Extension Radon Education Program offers low-cost radon test kits to Georgia residents [6].
Texas: The Texas Department of State Health Services says its radon program is now managed by Texas Tech University [5], which runs the Texas Radon Information site and offers a free test kit request [7].

Rules on radon testing, disclosure and contractor certification can differ by state. For your situation, check with your state program or your real estate agent.

Next steps

If your result is 4.0 pCi/L or higher, or between 2.0 and 4.0 and you want it lower, see what radon testing and mitigation costs. While you're thinking about air safety, read where to put smoke and carbon monoxide detectors. HomeCloud is a licensed general contractor that evaluates homes and prices and does the repairs, and you can request an estimate.