What Homeowners Should Know About Radon Levels Illinois

When I bought my first house in the Metro East area, back when I was still learning the difference between a sump pump and a French drain, the inspector mentioned radon. He said it was worth testing but didn't push hard. So I bought a short-term radon test kit from a hardware store, left it in the basement for three days, and sent it off. The number that came back was around 5.0 pCi/L. The EPA action level is 4.0. I had a problem.

That experience taught me more about radon in Illinois than any brochure could. The reality is that radon levels Illinois can vary wildly even between two houses on the same street. One neighbor might test at 2.0 pCi/L, perfectly acceptable, while the house next door hits 8.0. The geology under our feet is layered and unpredictable, and the Metro East region sits on glacial till and fractured limestone that can channel radon gas straight into a basement slab.

Why Radon Matters in Illinois

Illinois has some of the highest average radon readings in the country, partly because of the state's geology and partly because of how our homes are built. The IL Department of Public Health keeps maps that show large swaths of the state in Zone 1, meaning predicted average indoor radon levels above 4.0 pCi/L. The Metro East counties, including parts around Belleville, Edwardsville, O'Fallon IL, and Collinsville, are right in that zone.

Radon is a radioactive gas that comes from the natural decay of uranium in soil and rock. You cannot see it, smell it, or taste it. The only way to know it is there is to test for it. And because radon levels Illinois are not uniform, a map can only tell you the risk category, not your actual exposure. The only reliable method is a proper radon test in your own home.

How Radon Gets Into a Home

Radon gas moves from the soil into a house through any opening between the building and the ground. Common entry points include cracks in concrete slabs, gaps around pipes, sump openings, crawl spaces, and even the porous nature of concrete itself. The pressure inside a typical home is slightly lower than the pressure in the soil around the foundation, so the house acts like a vacuum, pulling radon gas indoors.

This is not a problem limited to old houses with crumbling foundations. I have seen brand new construction in Edwardsville test above 10.0 pCi/L because the builders did not install any radon-resistant features. The house was tight, energy-efficient, and pulling radon from the soil like a straw. Modern building codes in Illinois do require some radon-resistant construction in high-risk areas, but the requirements are not always enforced uniformly, and they do not guarantee low levels. Testing is still necessary.

Testing: Short-Term vs. Long-Term

There are two main approaches to radon testing, and each serves a different purpose. A short-term radon test stays in the home for two to seven days. These are the most common tests sold in hardware stores and the ones typically used during a real estate transaction. They give a quick snapshot, but radon levels fluctuate with weather, season, and how the home is used. A short-term test can be influenced by a heavy rain, an open window, or a change in the heating system.

A long-term radon test runs for 90 days to a full year and gives a much more accurate picture of the annual average exposure. Because radon levels change day to day and season to season, a long-term test smooths out those variations. The National Radon Program recommends a long-term test for every home. But I understand that most people start with a short-term test, especially if they are in the middle of buying or selling a home. The key is to follow the instructions exactly. Close the windows, keep doors closed as much as possible, and place the radon detector in the lowest livable level of the house.

In the Metro East area, companies like Air Sense Environmental offer both types of testing and can interpret the results in the context of local conditions. They also handle the more technical aspects, like placing multiple detectors in a large home or dealing with unusual foundation layouts.

What to Do With a High Result

If your test comes back above 4.0 pCi/L, the EPA recommends taking action to reduce the level. The most common and effective method is sub-slab depressurization, also called soil suction. This involves drilling a small hole through the basement floor, creating a suction point under the slab, and venting the radon gas to the outside using a fan and pipe system. The pipe runs up the side of the house and exits above the roofline, so the gas disperses safely into the air.

Sub-slab depressurization can reduce radon levels by 50 to 99 percent, depending on the house. I have seen it drop a reading from 12.0 pCi/L to 1.5 pCi/L in a house in Collinsville. The system runs continuously, uses very little electricity, and is usually invisible from the inside. The only visible part is the vent pipe outside, which can be painted to match the siding.

Other mitigation methods include sealing cracks and openings in the foundation, improving ventilation in the basement, and installing a heat recovery ventilator to exchange indoor air with outdoor air. But for most homes in this region, sub-slab depressurization is the proven solution. A professional radon mitigation contractor can evaluate the specific conditions of your home and recommend the right approach.

Radon in the Real Estate Transaction

If you are selling a home in the Metro East area, a radon test is not required by Illinois law, but it has become a common contingency in purchase agreements. Buyers are increasingly aware of radon, especially if they have read about radon levels Illinois online or heard stories from neighbors. A clean test can make the sale smoother. A high test does not have to kill the deal, but it usually means the seller will need to pay for mitigation or credit the buyer at closing.

I have seen sellers panic when a test comes back high, thinking they have a health hazard that will scare off buyers. But radon is a fixable problem. A properly installed mitigation system adds value to the home and removes the uncertainty. In fact, many buyers see a pre-installed system as a plus. They know the house has been taken care of.

Seasonal and Weather Factors

Radon levels are not static. They rise and fall with barometric pressure, rainfall, temperature, and even wind. In the winter, when homes are closed up tight and the furnace runs, radon levels often climb. The same house tested in July might show a reading of 3.5, but tested in January it could hit 6.0. That is why a long-term test is more reliable, and why short-term tests should be interpreted with caution.

If you are using a short-term test, try to do it during a period of normal weather. Avoid testing during a heavy rainstorm or when the ground is frozen solid. And always run the test with the house in closed conditions, meaning windows and doors closed as much as possible, except for normal entry and exit.

Final Thoughts on Testing and Mitigation

Radon is a serious issue, but it is not mysterious or impossible to handle. The first step is testing. You can order a kit online, buy one at a local hardware store, or hire a professional like Air Sense Environmental to do the testing for you. The cost is small compared to the peace of mind. If the test shows a problem, mitigation is straightforward and effective.

In the Metro East area, the combination of geology and housing stock means that radon levels Illinois are worth paying attention to. Whether you live in Belleville, Edwardsville, O'Fallon IL, Collinsville, or anywhere in between, a simple test can tell you what you need to know. And if the number is high, you can fix it. I have been through the process myself, and I can tell you that the relief of knowing the air in your home is safe is worth every bit of effort.