What Causes Radon in Homes?

House cutaway shows how radon enters.
credit: Image © ResCom Inspections LLC
Radon infiltrates through gaps and cracks in your foundation and through walls, floors, and windows.

Radon is a naturally occurring radioactive gas emitted by uranium ore as a product of its radioactive decay. Uranium is commonly present in igneous (volcanically produced) rock such as granite, and its radon gas emissions can be found in soils of all 50 states of the U.S.

Radon gas is released naturally in the outdoor environment, but outdoors it is much too diffuse to be harmful. It's only when radon is able to seep into confined spaces and settle there that it becomes a health hazard. Radon may also be present in water, especially the water of private wells, and even municipal well water can be a source of radon unless it's properly treated. Generally, water from surface sources like rivers, lakes, or reservoirs does not contain radon because the gas dissipates quickly when mixed with the open air.

Chemical symbol for radon
credit: Image © Everest Inspections
Radon is a radioactive gas, atomic number 86.

The Chemistry of Radon

Chemically, radon is an element, a single atom. It's classified as a noble gas, one of a group of elements that resist combining with other elements to form compound molecules. That means that radon gas atoms are smaller than those of air or water molecules and thus can more easily penetrate common building materials such as concrete, plastic sheeting, gypsum wallboard and wood paneling.

Radon atoms are nine times heavier than air, so radon gas naturally seeks the lowest levels of a home. Unless displaced with an inflow of fresh air, it accumulates at these low levels of the home, where it can build to dangerous levels. In addition to infiltrating your home through the walls and floors themselves, radon gains access through cracks in the foundation and where gaps around pipes or fixtures have not been adequately sealed.

Short-term radon testing kit.
credit: Image © Central Virginia Testing
Passive radon testing uses charcoal canisters.

Detecting Radon in Your Home

The presence of radon is not something you can see or smell. It can only be determined by testing. Do-it-yourself home testing kits are available in many forms and are sometimes available at no cost from municipalities. These home testing devices are known as passive tests. Passive test kits are available in two categories: short-term and long-term. Short-term tests are typically left in place for two to seven days. Long-term tests require from 90 days to as much as a year. In either case, the homeowner is instructed to place the device in a low area for the prescribed amount of time and then to send the exposed unit to a laboratory for analysis. Passive devices, especially the ones that are set for only a few days, are only approximate in their accuracy and are most appropriately used to signal whether a problem may exist.

An accurate, conclusive reading of the radon level in your home requires an active testing device. These active devices track and record the radon levels in your home over time and are administered by air quality specialists. These specialists should also be able to advise you on next steps should the radon concentration in your home prove problematic.

If you are building a new home, find out if radon has been a problem in your area. While radon contamination levels can vary from house to house, a greater determinant is the soil composition and your region's geology, so the prevalence of high readings locally is a strong indicator. Installing a radon reduction system as the home is built will be less expensive and likely more effective than one added later.

Confronting the Danger of Radon

Radon level is expressed in picocuries per liter, abbreviated as pCi/L. The Environmental Protection Agency recommends that you take action to mitigate the radon contamination in your home if testing indicates levels of 4 pCi/L or higher. Naturally, once mitigation is in place, you will want to retest.

The EPA has estimated that radon is responsible for approximately 21,000 lung cancer deaths per year. After smoking, it's the second highest cause of deaths from lung cancer. Smokers are especially susceptible to the effects of radon exposure, accounting for about 85 percent of those 21,000 deaths.

The hazard presented by radon comes from prolonged exposure to unacceptably high levels of the gas. The need to know and control the concentration level of radon in your home is a cause for action but not one for panic. Begin the process of testing and then, if necessary, explore the radon mitigation options available to you. Your state radon office should be able to provide you with a list of qualified contractors.