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Frequently Asked Questions: Indoor Exposures - Radon

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Q:  What is radon?

A:  Radon (Rn) is a naturally occurring radioactive gas produced by the breakdown of uranium in soil, rock, and water. Because the air pressure inside a home is often lower than the pressure in the soil underneath and surrounding a home’s foundation, a home acts as a vacuum and draws the gas through foundation cracks and other openings.  Radon levels are often represented as picocuries per liter of air or pCi/L. The average indoor air radon level is 1.3 pCi/L of air. The average outdoor ambient level is 0.4 pCi/L. Radon is odorless and colorless. On a U.S. map, Montana is listed as a Zone 1 region for radon. Zone 1 regions are those with the highest natural occurance of radon where the predicted average indoor levels are greater than 4 pCi/L.

Q: What are the health risks of radon exposure?

A:  Once inside the home, radon and it’s decay products can be inhaled into the lungs, resulting in cellular damage that can lead to disease. Radon exposure is the 2nd leading cause of lung cancer (tobacco smoke being #1) and it is estimated that in the U.S. > 20,000 deaths/yr are attributable to radon exposure. Another way of representing this is that about 14% of all lung cancers are from radon. If you smoke and your home has high radon levels, the risk of developing lung cancer is higher than either of the two alone.

Q:  Should I test my home for radon?

A:  The only way to know your radon level is to test. Tests can be either short term (2-90 days) or long term (> 90days). Short term tests are inexpensive and available at the Health Department and local hardware stores. Test kits are also available at the radon hotline 1-800-SOS-RADON (767-7236).

Q:  Are levels of radon below 4pCi/L considered safe?

A: The EPA has established that a level of 4pCi/L is the action level or the level above which homes should be fixed. Does this mean that it is safe if you are at 3.9pCi/L? The answer is no. There is no safe level of radiation. A radon level of 4.0pCi/L is equal to 200 chest x-rays per year or 16 cigarettes per day. The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels, about 0.4 pCi/L.

Q:  If my neighbor's home has low levels of radon can I assume my home is safe?

A:  Radon levels can vary wildly between homes. Variability in the housing techniques, age, materials, heating/air conditioning systems, geological features, venting, floor spaces, additions, foundation, plumbing, etc. all can influence levels. The only way to know your radon levels is to test.

Q:  How can I fix my radon problem?

A:  Locate a qualified radon mitigation contractor. Montana does not require radon mitigation contractors to be certified so do due diligence on any contractor claiming to be qualified. The National Environmental Health Association (NEHA) and NRPP (National Radon Proficiency Program) do offer certifications. The good news is that radon reduction systems work. In most cases mitigation systems can reduce radon exposure by 99%. Many contractors will tell you that if the soil is permeable enough to emit radon into home, it is permeable enough to mitigate. Radon mitigation can be a relatively inexpensive home repair ($800-$2500). Contact the State radon office (1-800-546-0483) or the Yellow pages to locate a radon contractor.

There are a variety of techniques used by contractors to mitigate radon levels including subslab suction, sump hole suction, submembrane suction in crawlspaces, sealing cracks, house pressurization, and air-to-air heat exchange. Since the house acts as a vacuum and draws radon inside, often times the most effective way to mitigate radon is to simply apply stronger suction to the soil underneath the house and vent it through a pipe to the outside air above the home.

 After successful installation, a radon reduction system can add value to a home. Inform potential buyers of the radon system – it can be a real selling point to know that a home has been made safe from radon.

Q:  What are some ways radon can be prevented while building a new home?

A:  Build the home to be radon resistant. A number of the same approaches used in mitigating (sealing, passive and active depressurization, etc.) can be more easily applied during the initial phases of construction than after a home has been built. Radon-resistant new construction has many advantages over remediation including aesthetics and efficiency. Additionally, the EPA has recently developed a new building label called Indoor airPLUS. The building practices incorporated as part of this label maximize radon reductions, moisture control, HVAC, and pest control. From the EPA’s website. 

By constructing homes that meet EPA's Indoor airPLUS specifications, builders can distinguish themselves by being among the first recognized by EPA to offer homes designed to truly deliver better indoor air quality. Participating builders can expect higher levels of quality assurance, improved reputation, reduced callback and warranty costs, and less business risk. Partners are also eligible to use Indoor airPLUS marketing materials and tools to help promote their qualified homes, access technical and marketing assistance, and receive awards. Go to to find out more information

Also see the publication: Building Radon Out: A Step-by-Step Guide On How To Build Radon-Resistant Homes on the EPA website (

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