How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
Can a mobile/manufactured home have a high radon problem?
Friday, July 20, 2018
This is what the United States Environmental Protection Agency (EPA) has to say about mobile homes and radon: “Unless these buildings are set up on piers without any skirting placed around them, interior vacuums can cause radon to enter these types of homes as well.” So, the EPA confirms that it is possible for a mobile home to have elevated radon levels. But, as we will explain later, it is less likely than in an average site-built home.
People that have heard about radon, but don’t know too much about it, typically fall into one of two camps. Either they think it’s a deadly gas and, if you have it in your home, you are doomed; or that it’s nothing to worry about, just some psuedo-science mumbo-jumbo that’s been blown out of proportion by the media. The truth falls between those two extremes.
Radon is a colorless, tasteless, odorless gas that is a Class A carcinogen, and the second leading cause of lung cancer, after smoking. Radon comes from the radioactive breakdown of naturally occurring uranium and radium, found in most soils. It’s important to know that a low level of radon is in the air we breathe every day, even outdoors. The health risk occurs when high levels of radon accumulate in a home.
The “interior vacuums” that the EPA refers to in their official radon statement is the natural chimney-effect that occurs in almost any home. The air pressure difference between the interior and exterior of a home draws in air around the bottom, then exhausts it through the upper portion. The diagram below shows how it works. Radon starts as a gas in the soil, and rises up into a site-built home through the inevitable cracks and small openings in the foundation, basement, or floor slab. But most manufactured homes have an advantage in that they are elevated, the crawl space has some ventilation, and the bottom of the home is sealed with the plastic sheet “belly board”—that is, as long as the ventilation is not blocked and the belly board remains intact and sealed. Also, some mobile homes have a plastic-sheet vapor barrier on the ground under the home that further limits radon. These built-in features can reduce the amount of radon that enters a manufactured home compared to a site-built home with a similar amount of radon in the soil below it. But, if there is a high level of radon to begin with, you may have an unsafe level of radon inside your home anyway and mitigation would be necessary.
Radon is measured in pico-curies per liter of air, and 4.0 pCi/L or higher is defined by the EPA as an unsafe level of interior air. If you live in an area of the U.S. known as having elevated radon readings, we recommend testing with a simple home-test kit available at most hardware and home improvement stores. In our area of Florida, Alachua County maintains a website with a map indicating the areas of the county that have been found to have high radon (http://radon.alachuacounty.us/). Many other parts of the U.S. have similar maps for your reference. Also, the U.S. Environmental Protection Agency’s radon homepage is at http://www.epa.gov/radon/ for more information on radon.
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