Homeowning 101: Radon

Radon has been in the news the last couple of months with some changes to Minnesota law, and the EPA designated January as Radon Action Month, so this week I’m taking a few minutes to give a quick overview of radon, the risks it poses, regulations and recommendations, and what you can do to protect yourself and your family. I’ve tried to walk that fine line between too vague for those wanting exact information and too technical for those looking for a quick read, so bear with me. The numbers are important, and so is accessibility.

First things first. Radon is a naturally occurring gas, a direct product of the radium that is created as uranium and thorium in the earth decay. It’s an element in its own right, the only radioactive one among the noble gases that you had the pleasure of learning about in high school chemistry class (Symbol: RN; Atomic number: 86). Though its very short half-life (3.8 days) makes it one of the rarest elements, there’s always some radon in the air around us as it seeps up from underground, and it has a tendency to get trapped and concentrated in buildings, including our homes. If the concentrations are too high, radon can pose some serious risks.

Before I get into too much detail on these risks and how to mitigate them, it’s worth getting to know just how radon works and what radon measurements mean. As we breathe radon in the air, radioactive particles from it can get trapped in our lungs and then release bursts of energy as the unstable atoms blast off excess energy. These bursts damage lung tissue and can cause lung cancer over time (multiple studies, two of which can be found here and here have confirmed the direct link between radon and lung cancer). Though no amount of radon is particularly good for us, it starts to get noticeably dangerous at concentrations of about 2 picocuries per liter, and the risk of health effects increases again sharply at about 4PCi/liter. What is a picocurie, you ask? Well, maybe you didn’t ask, but I did, and now I’m sharing whether you like it or not. A picocurie is one trillionth of a curie, which probably doesn’t clear much up unless you know that a curie is a unit of measure for the intensity of radioactive activity. So measuring in picocuries of radon is measuring how many radioactive disintegrations occur in a liter in a fixed time. If air has one picocurie of radon per liter, it means that there are 2.22 of the tissue-damaging bursts of energy in each liter of air each minute.

Outside, the air has an average radon level of 0.4PCi/liter, and the indoor average is 1.3PCi/L, so a concentration of 2PCi/L is elevated, and a concentration of 4PCi/L is quite high; at these higher levels the risk of radon-related lung cancer increases sharply. According to the EPA, at the average indoor concentration of 1.3 PCi/L, about 2 non-smokers in a thousand could end up with radon-related lung cancer; at 2PCi/L that number doubles to 4 (the same risk of dying of poison), and at 4PCi/L it almost doubles again to 7 (the same risk as dying in a car crash). For smokers, the story is much, much worse, as you might expect: at 2PCi/L radon could contribute to lung cancer in 32 of a thousand people and at 4PCi/L that number jumps to 62. In recent years, radon has been the second leading cause of lung cancer, right behind smoking, and the WHO says that it is responsible for some 15% of lung cancers worldwide. According to EPA estimates, radon-related lung cancer kills some 21,000 people per year, including 2,900 people who have never smoked. Just for context, about 17,400 people per year die because of drunk driving, according to CDC and National Safety Council reports in 2005 and 2006.

The EPA estimates that about 1 in 15 homes in the US has a radon level above 4PCi/L, and any age, style, or configuration of house can be affected. And because of Minnesota’s geology – lots of granite bedrock with uranium happily decaying in it – we are particularly prone to high concentrations of radon (not being able to open a window for months at a time doesn’t help, either). According to the Minnesota Department of Health, the average level in Minnesota is actually three times the national average, and instead of 1 in 15 homes having high radon levels, our number is closer to 2 in 5. In Rice county, 3 in 5 homes have levels above 4PCi/L, with an average of about 5.9PCi/L, according to Rice County public health. Sort of horrifying, right? Fortunately, it’s actually very easy to test radon concentrations in your home and to bring levels down if they’re elevated.

The first step is to test your home’s radon levels; because radon is colorless and odorless and exposure causes no immediate symptoms, and because radon levels vary widely even in a small area, a test is really the only way to determine your home’s radon level. The EPA recommends testing when you move in, every two years after that, and if you make structural changes to your home or begin using a lower level like a basement more often (because radon enters the home from the ground, lower levels have higher concentrations than upper storeys). Testing is surprisingly easy to do and mostly consists of leaving a testing device alone in your home for a while and then having the levels read from the device. You can do it yourself or hire a professional, and there are two main types of test, a short-term test and a longer term one. The short-term test stays in your house anywhere from two to 90 days, depending on what kind of test you’re using, and is good to give you a quick picture of current radon levels. The long-term test stays for more than 90 days and is more reliable for telling you the year-round average level in your home. One common strategy for getting an accurate picture is to take a short-term test and follow up with another test if the initial reading is in the danger zone.

If you want to have a professional perform the test for you, you can find one by going to the Minnesota Department of Health’s Radon Service Providers page and search for one near where you live. Personally, I’d call Premier Property Inspections if you live in the Northfield Area; their phone number is 612-849-2221. If you’re administering your own radon test in Rice County, you can get a kit for free either at Rice County Public House in the Government Services building in Faribault or in the Rice County office in Northfield City Hall (while supplies last!). You can also order a kit online or buy one at a home-improvement store. Many of these kits include mailers to return the device for analysis at the end of the test period, because the reading should be done by licensed professionals.

Once you have the kit, make sure you are doing the test on the lowest occupied level of your home and in a room that is used regularly (but not a kitchen or bathroom, since we use fans so much more often in those rooms); the device should be at least 20 inches from the floor and away from exterior walls, drafts, excessive heat, and other sorts of atmospheric disturbances. During the test, keep windows and outside doors closed as much as possible, and don’t use fans or other things that might bring in air from outdoors. If there’s unusually windy weather in the forecast, it might be best to wait until it passes, and if you’re using a very short term test of only a few days, keep windows and doors closed for 12 hours before you begin as well. The idea behind all of this is that if you’re bringing in too much fresh air, you won’t get an accurate reading of the radon that is hanging out in your home. You can still use ventilation fans for short periods, and if you already have a radon mitigation system, it can of course be on. Once the test is done, package it up and send it to whatever lab the packaging tells you to. They’ll send your results back within a few weeks.

Radon test kit


If your test results come back showing a radon level of 4PCi/L or higher, you should take fairly immediate action bring that level down through a mitigation system, and if the level is between two and four PCi/L, you should consider a mitigation system. The conventional wisdom on this has changed recently, so you’ll still see a lot of information that says only measurements over four should be acted on. Given what we know about the health effects of radon, experts are now encouraging people to consider mitigating radon levels anywhere above 2PCi/L.

Most mitigation systems involve installing a vent pipe and fan to pull air out from under your home so radon doesn’t have a chance to become trapped there and seep in through cracks and foundations. According to a recent article from WCCO, radon mitigation for an average size home in our area costs about $1700. These systems should be installed by licensed professionals, and the Minnesota Department of Health has a very useful website to help you locate these professionals and know what to look for when hiring. In 2018, the Minnesota Legislature passed statutes requiring that all radon contractors be licensed by the state. This Minnesota Radon Licensing Act also allows for homeowners to have radon mitigation inspected and for the Department of Health to maintain a database of these repairs. The changes were set to take effect on January 1st of this year, but due to an injunction, the statutes applying to radon mitigation professionals may not be enforced until further notice. Note that this applies only to mitigation in residences. Anyone who is testing in a building they don’t own or lease or performing radon mitigation in non-residential buildings must be licensed, as must the laboratories that analyze the results of radon tests. 

Of course, radon is also an issue when you’re buying or selling a home or when you’re considering new construction. Though radon tests are not required as part of a real estate transaction, the EPA and other agencies and organizations strongly recommend them, and Minnesota does require sellers to disclose any information they possess about radon to potential buyers, including whether the home has been tested, the radon levels recorded in those tests, and whether any radon mitigation has taken place, as well as information about whatever system is in place. The state also requires sellers to supply a warning statement and 2-page publication as part of the disclosure statement. 


Since 2009, Minnesota has required that new homes include passive radon resistant features. Passive features are those that are meant to limit radon’s ability to infiltrate buildings without actively moving air around. The most common passive strategies include having a permeable layer under the foundation to allow air to move away from the structure instead of through the foundation, putting a plastic sheeting barrier between this layer and the foundation, sealing and caulking openings in foundation walls, running a pipe from the permeable layer through the house to the roof to allow radon to move past the house rather than into it, and placing an electrical box in the attic to allow for easier installation of a fan later. These systems are highly effective, and it’s much less expensive to include them in new construction (typically between $250 and $750 in additional costs, according to the EPA) than it is to install a mitigation system later. They have the added bonus of making it very easy to activate the system – essentially to add a fan to draw air through the vent pipe – later if radon levels are still high, though the Department of Health in Minnesota actively encourages builders to install the fan during initial construction.

If you want to know more, the EPA and Minnesota Department of Health both have extensive websites dedicated to the hazards posed by radon and procedures for testing and mitigation. As for me, I’ll be looking into having our home retested in the near future, because there’s no sense messing around with a hazard so very easy to counteract.


Interactive Map for Minnesota