Why Every St. Louis Homeowner Should Consider a Home Radon Test

If you own a home in St. Louis, you already know the region has its share of basement flooding, tricky clay soils, and older construction. But one hazard you cannot see, smell, or taste is radon. This radioactive gas seeps up from the ground, and the geology of eastern Missouri makes it a real concern. I have spent years working with local homeowners, and the single most useful step I can recommend is a proper home radon test. Not the kind you buy at a big-box store and mail away, but a professional assessment that gives you a clear, defensible reading.

Radon is a decay product of uranium, which is naturally present in the soil and rock under much of the St. Louis area. As it breaks down, radon gas moves through pores in the soil and can enter your home through cracks in the foundation, gaps around pipes, or even through the crawl space. Once inside, it can accumulate to levels that pose a serious health risk. The EPA estimates that radon causes about 21,000 lung cancer deaths per year in the United States. That is a number that should get your attention.

I have seen too many homeowners assume that because their neighbor tested low, they are safe. Radon levels can vary dramatically from one lot to the next, even on the same street. The only way to know your situation is to run a home radon test. And I mean a real test, not a quick screening with a charcoal canister that you leave out for a few days and then forget about. A professional test uses a continuous radon monitor, which records levels over a set period and gives you an hour-by-hour picture. That matters because radon levels change with weather, barometric pressure, and how you run your HVAC system.

What a Professional Home Radon Test Involves

A proper home radon test starts with a conversation about your house. Is there a basement? Is it finished or unfinished? Do you have a crawl space? Is the slab on grade? The technician from Air Sense Environmental will place a continuous radon monitor in the lowest livable area of the home, typically the basement or the first floor if there is no basement. The monitor runs for at least 48 hours, often longer for a long-term radon test, which can last 90 days or more. The device takes readings every hour, and at the end of the test, the data is downloaded and analyzed.

One thing I appreciate about this approach is that it eliminates the guesswork. With a radon test kit you buy at a hardware store, you have to follow exact instructions about keeping windows closed, avoiding exhaust fans, and mailing the kit within a specific window. If you slip up, the results are meaningless. A continuous monitor does not rely on your memory. It logs everything, and the technician can see if any unusual events, like a storm or a furnace malfunction, skewed the numbers. That kind of detail is invaluable when you are trying to decide whether to invest in a radon mitigation system.

Short-Term vs. Long-Term Testing

The two main approaches are a short-term radon test and a long-term radon test. A short-term test, usually two to seven days, gives you a quick snapshot. It is useful during a home inspection when you are buying or selling a property and need answers fast. But it has limits. Weather can swing the numbers. A short-term test might show high levels during a cold snap when the house is sealed tight, and low levels during a warm spell when windows are open. That does not mean the problem is gone.

A long-term radon test, on the other hand, runs for three months to a year. It captures seasonal variations and gives you an annual average. That is the number the EPA uses to determine whether you need action. If your long-term average is above 4 picocuries per liter (pCi/L), the EPA recommends installing a radon mitigation system. I have seen homes in St. Louis with readings over 20 pCi/L. Those are not rare outliers. They are common in certain neighborhoods built on glacial till or limestone bedrock.

If you are selling a home, a short-term test is usually enough to satisfy a buyer's radon contingency. But if you are buying, I would push for a longer test if time allows. A home inspection often happens over a few days, so a short-term test is the standard. Just understand that it is a screening tool, not a definitive answer. If the short-term test comes back high, do not panic. It means you should do a follow-up long-term test or move straight to mitigation.

What Happens If Levels Are High?

If your home radon test shows elevated radon levels, the next step is radon remediation. The most common method is sub-slab depressurization, sometimes called soil suction. A contractor drills a small hole through the basement floor, inserts a pipe, and attaches a fan that draws the radon-laced air from beneath the slab and vents it safely above the roofline. It is a straightforward fix, usually costing between $800 and $2,500 depending on the house. For homes with a crawl space, a similar system can be installed under a vapor barrier.

I have seen this work in dozens of St. Louis homes. After installation, the radon levels almost always drop below 2 pCi/L, well under the EPA action level. The system runs continuously and uses very little electricity. It does not require any changes to your daily routine. You do not need to seal your basement or avoid the laundry room. It just quietly does its job.

Some homeowners ask whether they can just seal cracks and call it done. Caulking and sealing can help, but it is rarely enough on its own. Radon can enter through invisible gaps in the slab, around sump pumps, or through the block walls themselves. A radon mitigation system is the only reliable way to bring levels down permanently.

The Health Rationale

The health effects of radon are not something to brush off. Radon is the second leading cause of lung cancer after smoking, and the leading cause among non-smokers. When you breathe in radon, its decay products attach to lung tissue and emit alpha particles that damage DNA. Over years of exposure, that damage can lead to cancer. The risk is cumulative, so the sooner you test and fix, the lower your lifetime risk.

I have had clients tell me they are healthy, they eat right, they exercise, and they do not want to worry. But radon does not care about your lifestyle. It is a physical hazard, like lead in water or asbestos in insulation. You cannot outrun it. The only rational response is to measure it and, if necessary, reduce it.

Why Local Expertise Matters

St. Louis has unique radon geology. The Missouri Department of Health and Senior Services publishes radon potential maps, and large swaths of the metro area are in Zone 1, meaning predicted average indoor radon levels above 4 pCi/L. That includes much of St. Louis County, St. Charles County, and the city itself. Yet many homeowners have never tested. I think part of the reason is that radon is invisible, and people assume that if they cannot see it, it must not be there. But the data says otherwise.

Air Sense Environmental focuses entirely on radon testing for St. Louis homes. They know which neighborhoods tend to run high, which foundation types are most vulnerable, and how to place a radon detector for an accurate reading. That kind of local knowledge makes a difference. A national chain might send you a generic radon test kit with instructions written for a house in Florida. A local professional understands that your basement has a sump pit, or that your crawl space has a dirt floor, and adjusts the test accordingly.

If you are doing a home inspection before a sale, ask the inspector whether they include a home radon test. Many do not. Some offer it as an add-on. If you are buying a home, make sure the test is done by someone who uses a continuous radon monitor, not a passive device. The extra cost is small, and the peace of mind is large.

Making the Decision

Testing for radon is not expensive. A professional test runs a couple hundred dollars. A mitigation system, if needed, is a few thousand. Compare that to the cost of treating lung cancer, or simply the worry of not knowing. For most St. Louis homeowners, the answer is clear. Get a home radon test. If the levels are low, you are done. If they are high, you fix it and move on. Either way, you have taken control of a risk that was invisible before.

I have done this work long enough to see the relief on people's faces when they get a low result. And I have seen the determination of those who get a high result and decide to mitigate. In both cases, they are better off than before. They know. And knowledge, in this case, is the difference between a hidden danger and a managed one.