What is it? – Uranium is present in the soil virtually everywhere on the planet. Uranium decays into radium (that green glow in the dark stuff), and radium decays into radon, a radioactive gas that freely moves through the soil.
How does it get into my house? – Your house is like a big smoke stack stuck in the ground. Its air is continually rising, leaving the basement like a warm air balloon and rising to the top floor, where it pushes against the walls and ceiling and leaks out. As the air leaves the basement, a vacuum is created at the basement floor, and underground air is literally sucked into the house. Most homes will change their entire volume of air every two or three hours through this process. About 20% of the air in the average home was drawn in from underground through this process.
Health effects – When radon decays, it shoots out a microscopic spark called an alpha particle (alpha radiation). When this happens in your lungs, it leaves a microscopic burn on your lung cells. The burn damages the cell’s DNA bonds. When the damaged cell replicates itself, the new, defective cell, is more receptive to invasion by carcinogens than a healthy lung cell. One out of 16 smokers and one out of 140 non-smokers exposed to a lifetime of 4 pCi/L of radon (the EPA action level) can expect to get lung cancer due to the radon exposure. Radon risk is linear, meaning that if you double the exposure, you double the risk. It’s estimated that someone in the 7 county Twin Cities metro area dies of lung cancer caused by radon every 72 hours. The EPA estimates that radon gas kills over 21,000 Americans annually.
How common is it? – 1 of 15 US homes, 2 of 5 Minnesota homes and 4 of 10 metro area homes exceed 4 pCi/L, the EPA’s “action level”. The chart below shows the radon levels in various Twin Cities zip code areas.
|% over 4 pCi/
|550xx North of 94
|550xx South of 94
Are some homes less likely to have radon? – Studies show that a home’s tightness, foundation type and soil type have no predictable effect on radon levels A home with an air exchanger, such as a VanEE, can have a radon level 20% to 50% below comparable homes, if the air exchanger is properly cleaned and balanced and runs continuously. Studies have also shown that it is not possible to do soil tests on a lot to predict whether a house on the site will have elevated radon.
Is a mitigated home stigmatized? – No more than a home that’s had an unsafe furnace removed. In fact, a mitigated home has several advantages.
No surprises: Your long-term radon level is usually guaranteed to be less than 4pCi/L.
Low radon level: The average radon level in Minnesota is 4.6 pCi/L, but most mitigated homes are less than 1 pCi/L.
Higher overall air quality: About 20% of the air in the average home was drawn in from the dank, humid area below the basement floor. This air often contributes to high humidity and may contain unhealthy spores of mold and mildew. But homes with an SSD system have virtually no underground air.
Granite countertops – We have never come across a home where granite tops were identified as a radon source, and I doubt if we ever will. For advice on testing your granite, see Granite Countertops and Radon Gas by AARST.