Don asks: Our house measures just over the EPA limit for radon. Is this something we should be concerned about or are the risks overblown? How effective are radon mitigation systems and what do they cost? — Doug M.
Steve Bliss, of BuildingAdvisor.com, responds: While radon stories rarely appear in the news anymore, the health risk from exposure to high levels is real and significant. Public health experts agree that radon is a leading cause of cancer in the U.S. It is the second leading cause of lung cancer and is responsible for approximately 20,000 deaths each year in the U.S., 3,000 more than are killed in drunk-driving accidents. Smokers are at the greatest risk, roughly ten times greater than non-smokers – because smoking and radon have a combined “synergistic” effect.
To put the risk in perspective, the lifetime cancer risk from living in a home with a radon level of 4 pCi/L (the EPA “action level”) is about 6 in 1000 – about the same risk you have of dying in a car crash. For smokers, the risk is 6 in 100, a pretty scary number. By comparison we don’t allow any substance in drinking water that poses a cancer risk greater than 1 in 100,000. The radiation level at 4pCi/L is 35 times higher than we accept for people living near nuclear waste sites. Because radon is invisible, odorless, and difficult to regulate since it occurs naturally, we tend to ignore it.
The EPA recommends corrective measures when indoor radon levels exceed of 4 pCi/L of air. This “action level” has become the threshold level for many real estate deals. The goal of mitigation work is to get the level below 2 pCi/L, closer to the national average of about 1.3 for indoor levels (vs. 0.4 for outdoors). There is nothing magical about the action level of 4. A level of 3 carries ¾ the risk of a level of 4 and so on. The World Health Organization recommends an action level of 2.7 pCi/L.
Radon is found in all 50 states, but those in EPA Zone 1 have the highest risk. Some neighborhoods have higher average levels than others, but two houses next door to each other can vary by a factor of 100.
Testing is easy and inexpensive and the only way to determine if you have a problem. Short-term tests of a week or less are good for screening purposes, but long-term tests are more accurate. The test should be done in the lowest level of house usable as living space.
Controlling radon levels is fairly easy in most homes. Typically, a high-quality inline fan is used to draw the gas out from below the crawlspace, slab, or basement, where radon enters a house though cracks and construction joints. PVC drain pipe directs the radon gas to the outdoors. Sometimes a sump, existing foundation drain, or hollow-core block wall can be used as a collection point, but often a hole gets drilled through the concrete slab (see photo).
The fan can go in an unoccupied attic or outdoors. You don’t want it in a location where it will send radon gas into your house in the event of a leak or break in the piping. A good quality installation is extremely quiet and the fan should last 10 years or more. I recently installed a system with the fan in an attic space adjacent to the master bedroom (see photos above). The fan noise is not detectable. Despite a long duct run with several elbows, basement radon levels have dropped from about 6pCi/L to under 0.4pCi/L, which is the average outdoor level.
Homes with course gravel or crushed stone below the slab are easier to fix than home with a dirt crawl space or a slab directly on dense soil (illustration below). If you hear a hollow sound when you tap on your basement floor, that’s a good indicator that you have a nice layer of stone beneath. With dense, impermeable soil under the slab, you will need a more powerful fan and may need multiple suction points through the slab, which can be determined with simple diagnostic testing. However, nearly all homes can be fixed by an experienced radon contractor. Typical costs range from $1,000 to $2,000 for a professional installation.
The EPA has excellent guides on radon risks, testing, treatment, and construction techniques. including what to look for in a radon mitigation contractor. Also, most states have a radon office or specialist as part of their state health department that can provide expert advice and often offer free testing services. — Steve Bliss, BuildingAdvisor
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