Featuring America's Home Inspector: Nationally Syndicated Columnist, Barry Stone

The House Detective:  by Barry Stone, Certified Home Inspector

Dear Barry: We are in the process of buying a house and were informed that the sellers installed a radon mitigation system last year. Radon levels before the system was installed were about 7 picocuries per liter. What should we do about this situation, and what are the effects of radon exposure to occupants?  Ananda

Dear Ananda:  If the mitigation system that was installed in the home has effectively reduced the radon level below 4 picocuries per liter, there is no need to worry. Ask the sellers for radon test results taken after the system was installed. If a follow-up test was not done, or if they do not have documentary results of the test, you should request that a test be done as a condition of the purchase.

Radon is a radioactive gas that is produced by the decay of uranium in the soil or in ground water. It is particularly common in areas where the soil contains granite or shale. Radon is regarded as the second highest cause of lung cancer (next to smoking) and is credited with approximately 21,000 deaths annually in the United States.

Radon gas is emitted from the earth worldwide, with an average outdoor level of 0.4 picocuries per liter. When radon emerges from the ground beneath a building, indoor levels can become concentrated. The average indoor radon level in American homes is about 1.3 picocuries per liter. The threshold level for concern, according to the EPA, is 4 picocuries per liter. When indoor radon is measured at that level, mitigation is recommended for the health and safety of occupants.

Fortunately, mitigation systems are simple and relatively inexpensive. The type most commonly used is known as the soil suction radon reduction system. It consists of vent pipes with a fan that pulls radon from beneath the building. For increased effectiveness, cracks and seams in the floor should be thoroughly sealed.

Again, be sure to verify that radon levels have been sufficiently lowered. You should also ask for proof that the mitigation system was installed by a contractor who is licensed as a radon mitigator.

For more information on radon, visit www.epa.gov/radon/pubs.