Radon testing when buying a house: options, results and fixes

Why test during a purchase

You cannot predict a home's radon level from its location. EPA says homes next to each other can have different levels, and testing is the only way to find out. During a purchase you have leverage: you can ask the seller to fix a problem or adjust the price before you own the house. After closing, the cost is yours.

Ask the seller for any previous results. If the home has a radon reduction system, ask for information about it. A good result from years ago, or one taken before a renovation, may not reflect the home now.

EPA's short-term testing options

EPA's guide recognizes that buyers work on deadlines. It recommends short-term options designed for real estate, all lasting at least 48 hours:

Passive devices, two at once. Place two short-term tests side by side in the same location for at least 48 hours. Fix the home if the average is 4 pCi/L or more.

Passive devices, one after another. Run one short-term test for at least 48 hours, then immediately a second identical test in the same spot. Fix the home if the average is 4 pCi/L or more.

Active device. Test with a continuous monitor for at least 48 hours. Fix the home if the average is 4 pCi/L or more.

EPA notes the trade-offs. Simultaneous tests improve precision, while sequential tests better reflect the seasonal average. Your state radon office can help you choose.

Where to test. EPA says to test in the lowest level of the home that could be used regularly, even if the seller does not use it, since you might turn the basement into a family room.

Interference. Opening windows, moving the device or running fans can skew results. EPA recommends steps to prevent or detect interference, and a qualified tester can explain the ones they use.

Reading the result

EPA's action level is 4 pCi/L. It estimates the average indoor level in U.S. homes at about 1.3 pCi/L and outdoor air at about 0.4 pCi/L. EPA also stresses that no level of radon is safe, so even results below 4 pCi/L can be worth reducing.

Results near 4 are uncertain. EPA's example: if two short-term tests average 4.1 pCi/L, there is about a 50 percent chance the year-round average is somewhat below or above 4. That is a reason to negotiate a fix rather than argue about decimals.

Putting radon in the contract

EPA's guide suggests the contract say where the test will be located, who will do it, what type of test, when, how results and costs will be shared, and when any mitigation will happen and who will pay. Settle these points before you sign.

Fixing a high level

EPA says even very high levels can be reduced. In existing homes, the cost of a mitigation system is about the same as other common home repairs, and EPA recommends getting estimates from one or more qualified mitigators. Many states license or certify radon professionals. Your state radon office can tell you how to check a contractor.

The bottom line

Test every home you are buying unless it is on the third floor or higher. Use one of EPA's short-term options in the lowest livable level, and write testing and mitigation into the contract. If the result is 4 pCi/L or more, negotiate a professional fix before closing.