Home Radon Levels Go From Low to Dangerous within 150 Feet

Building Clean and its Habitat for Humanity partner in Rochester, N.Y., have found a cautionary example of how radon exposure can vary greatly even in the same neighborhood.

By Michael Miranda, LEED AP, HERS Rater, Building Clean Outreach Manager


Radon is a naturally occurring radioactive gas that can cause lung cancer. Radon is released as radioactive metals uranium, thorium, and radium break down in rocks, soil, and groundwater. It enters homes primarily through openings in the basement or slab. You can’t see or smell radon. The only way to know your level of exposure is to test for it.

After reviewing state historical testing data for radon levels in the Rochester area, Building Clean suggested that Flower City Habitat for Humanity—a builder of high-quality and healthy affordable housing—perform radon testing on its latest homes. Flower City Habitat for Humanity conducted radon testing on four new homes built within 300 feet of each other.


Despite the four homes having been built the same way—by the same builder and during the same time period—the tests found that radon levels varied significantly within just 150 feet. The results found low levels of radon on one side of the street but dangerous levels on the other side. 

Radon testing in three of the homes on the same side of the street found levels of 1.0 pCi/L or less. Testing in the fourth home, which is across the street from the other three homes, found a radon level of 8.12 pCi/L. To put these numbers in context, the U.S. Environmental Protection Agency (EPA) considers it necessary to remediate a home if the radon level is 4 pCi/L or higher, and urges remediation if the level is between 2 and 4 pCi/L. Internationally, the World Health Organization recommends action if radon levels are above 2.7 pCi/L.

Luckily Flower City Habitat has a valued volunteer in Jim Bradley, who has been working closely with the Building Clean team and has experience dealing with radon.

To test the Flower City Habitat homes, Jim used his own electronic radon monitor. Testing was performed in the basements of the homes while the homes were in the final phases of construction with finishes and appliances being installed. The electronic radon monitor has a screen that constantly displays the long-term and short-term radon level, updated daily and hourly respectively.

The electronic radon monitor results were confirmed with a traditional short-term radon test kit that is mailed to a lab for analysis. The short-term radon test kit revealed that sealing the sump pump cover produced a small reduction in radon levels.


The EPA classifies every U.S. county into one of three radon zones—Zone 1, 2, or 3—based on predicted average indoor radon levels. The four homes that were tested are in a Radon Zone 2—counties with predicted average indoor radon levels from 2 to 4 pCi/L. During its Rochester work, Building Clean found New York State Department of Health data showing that 10% of homes with basements in Rochester have radon levels greater than 4 pCi/L.

Zone 1 counties are expected to have the highest radon levels, with predicted average indoor levels greater than 4 pCi/L. Zone 3 counties are expected to have the lowest radon levels with predicted average indoor levels less than 2 pCi/L.

The EPA stresses that no matter where you live, and no matter the radon zone, the best practice is to test your home for radon. In multifamily buildings, the EPA and the Surgeon General recommend testing all units below the third floor for radon.

After the test findings, the next step was to install a pipe from the sealed sump pump cover to the outdoors, so that radon under the foundation has an easy path out before having a chance to enter the house. Installing the pipe is called “passive radon ventilation,” but that is not always enough and a fan (powered ventilation) is sometimes needed to pull the radon out. Follow-up electronic radon monitor results showed no impact from passive ventilation connected to the sump pump cover, and powered fan ventilation would be needed.


With energy efficiency and healthy homes being more valued, closing openings that let in pests and pollution and let out expensive conditioned air also has the potential to change home radon levels. Home improvement work such as installing a sump pump, adding a bath fan in the basement, air-sealing, weatherization, and more may allow more radon in or stop it from leaving. Re-testing your home’s radon levels after making these types of improvements is highly recommended. Because radon levels tend to vary from day to day and season to season, a short-term test (2 to 90 days) is less likely than a long-term test (more than 90 days) to tell you your year-round average radon level.

There are two types of do-it-yourself radon test methods, a traditional radon test kit that is mailed to a lab for analysis and an electronic radon monitor that displays radon results on a screen or a smart-phone app.

Both methods can be used to perform a short-term test (2 to 90 days) and a long-term test (more than 90 days). Before buying a mail-in short-term radon test kit, be sure to confirm how long you can test as some only test for 2 to 7 days.

Builders might consider investing in an electronic radon monitor, like the one Flower City Habitat for Humanity used, so they can monitor radon levels within multiple homes and buildings. According to the EPA, nearly 1 out of every 15 homes in the United States is likely to have elevated radon levels. Radon is estimated to cause about 21,000 deaths from lung cancer each year.


Remediation techniques can differ by home. An experienced radon mitigation professional should be consulted to reduce elevated radon levels.

Building Clean offers free assistance to non-profit affordable housing organizations to help build healthier and energy-efficient affordable housing with American-made building products. If you are interested in learning more about Building Clean’s free services, email danap@bgafoundation.org.

Radon Testing Resources

  • Check with the local or state health or environmental protection agency to see if they offer radon test kits for low or no cost.
  • The EPA lists organizations within your state that you can contact about possible discounted or free radon test kits.
  • If you would like to have a professional conduct the radon testing, the EPA offers direction.

Resources to Reduce Radon Levels

If elevated radon levels are found, the following information can help:

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