Radon: Facts and Advice

Radon Testing in Michigan

Everything you need to understand the geology and building science aspects of radon. Michigan maps show where it comes from in our state. Other material, on what radon is, how it gets into homes, how to measure it, and how much is too much, is of general interest, as is the information, including photos, on how to reduce indoor radon. Michigan homeowners, homebuyers, REALTORS®, property managers and day care operators will find this portion of our website of of special interest.

What Makes Michigan Radon Different from the Rest of the Country?

Radon in water is not a problem in Michigan, with the possible exception of mountainous areas of the Upper Peninsula. The reason: Our radon is emanating from shallow glacial till, while water is drawn from deeper aquifers where it is never in contact with uranium-bearing rocks.

The conventional wisdom is that your neighbor’s radon reading says very little about what you will find in your own home. That may be true of geographic areas where the uranium is in well-defined seams in rock, but not in most of the lower peninsula of Michigan. Radon here is characterized by broad swaths of relatively uniform glacial rocks. Except in parts of the UP, in Michigan if your neighbor has a radon problem, it’s almost a certainty that you do too.

Basics of Radon (Michigan and Elsewhere)

The EPA classifies much of Michigan as a radon hot spot, a result of uranium dropped off by the glaciers thousands of years ago. In some areas (notably Hillsdale and Lenawee counties, and parts of Washtenaw, Livingston, Wayne and Oakland counties), most homes will “fail” the radon test. Maps and further details are found here.

Over the course of 5 billion years, an atom of uranium in the soil will be transformed by radioactive decay into an atom of ordinary lead. For only 4 days in this time (!), the atom is a gas (Radon) that can move through the soil; the rest of the time it’s a solid, unable to move and cause mischief.

If our radon atom is to enter the breathing space of a home it must move rather quickly in its brief lifetime. This means that problem homes are either built very close to the source, or are on loose soil (sand or gravel) that allows easy migration of the gas.

Radon concentrations are measured in picoCuries per liter (pCi/l). One pCi produces 2.2 radioactive events per minute. The US EPA has established an Action Level of 4 pCi/l for residential radon.

Radon concentrations tend to be the highest in rooms near the source, i.e. that contact the soil. In a typical two-story home, the average concentration on the first floor is 50-70% of that in the basement, and the second floor concentration is somewhat higher. Why is that?

Radon concentrations depend strongly on weather. Winter readings are higher than those in summer (even in closed-up homes) for three reasons:

• A house acts like a giant chimney, with warm air rising and escaping at the top, creating a slight vacuum (“draft”) at the bottom. In winter, the warm air in the house is quite buoyant, and so this chimney effect is stronger, creating a stronger vacuum in the basement and drawing in more “soil gas.”
• Most furnaces steal air from the basement for combustion, sending it up the chimney. That air has to be replaced (otherwise the house would deflate), and some of the replacement will come from underground.
• When the ground freezes, there is no exchange of air between ground and atmosphere. In other words, there is nowhere else for the radon to go except through homes.

The magnitude of the effect varies from home to home. In extreme cases winter radon readings may be double those found in summer.

Wind perpendicular to the ridgeline creates lift (just as it would in passing over an airplane wing), sharply increasing the stack effect and raising radon levels.

More Info

Now you know more than 99% of the public about the basics of radon. For specific info on radon topics (testing, fixing, water, etc.) please explore the links in the left panel. The FAQ would be a good place to start.