Why Radon Testing Apartments Is Essential for St. Louis Property Owners and Managers

If you manage or own an apartment building in St. Louis, you have probably heard about radon. You might even know it is a naturally occurring radioactive gas that can seep into buildings from the soil. But what you might not realize is how common elevated radon levels are in the St. Louis area, especially in older multifamily housing with basements or slab-on-grade foundations. I have spent years working in this field, and I can tell you that radon testing apartments is not just a good idea. It is a responsibility that touches on health, legal obligations, and property value.

Over the past decade, I have been involved in hundreds of tests across commercial and multifamily buildings. The single biggest gap I see is that many property owners assume radon is only a problem in single-family homes. That assumption can be costly. When I talk to managers of apartment complexes, they often tell me they never considered testing because they thought the issue was confined to houses with basements. But radon does not discriminate. It enters any building that sits on soil containing uranium, which is common in much of the Midwest. In St. Louis, the geology is a contributing factor, and we see elevated readings in apartments, condos, and commercial spaces regularly.

Let me walk you through why radon testing apartments is something you should prioritize, how the testing works in practice, and what the results mean for your tenants and your bottom line.

The Health Imperative and Tenant Notification

The EPA has set a recommended action level of 4 picocuries per liter (pCi/L) for radon in indoor air. Above that level, the agency suggests taking steps to reduce exposure. Radon is the second leading cause of lung cancer after smoking, and it is responsible for an estimated 21,000 lung cancer deaths per year in the United States. For tenants living in your apartments, the risk is real. And if you are a property manager, you have a duty to ensure a safe living environment.

Tenant notification laws vary by state, but Missouri does not have a specific statute requiring landlords to test for radon. However, the federal HUD guidelines for radon in multifamily housing are increasingly strict. If you have a property that is financed or insured by HUD, you are expected to follow their radon policies. That usually means testing all ground-floor units and common areas, and if levels are high, installing radon mitigation systems. I have worked on several HUD-related projects in St. Louis, and the agency is serious about this. They require testing by a licensed radon professional, and they accept only certain types of radon detectors.

Beyond legal requirements, there is the question of tenant notification. Even if you are not required to test, if you do test and find elevated levels, you generally need to inform tenants. Some property owners worry about liability, but in my experience, being proactive builds trust. A simple letter explaining that you tested, what the results were, and what steps you are taking goes a long way. It shows you care about their health.

How Radon Testing Works in Apartments

Testing an apartment building is different from testing a single home. In a single-family house, you place a detector in the lowest livable area. In multifamily housing, you need to sample multiple units, especially those on the ground floor and basement levels. The goal is to get a representative picture of the entire building.

There are several types of radon detectors commonly used. The most basic are charcoal canisters, which are cheap and easy to deploy. You leave them in place for two to seven days, then send them to a lab for analysis. They work well for a short-term test, but they can be affected by humidity and temperature. Another option is an alpha track detector, which uses a plastic film that records alpha particles. These are good for long-term tests, typically 90 days to a year, and they give a more accurate annual average.

For commercial and multifamily buildings, I often recommend a continuous radon monitor. These are electronic devices that measure radon levels hour by hour. They cost more, but they provide real-time data and can detect fluctuations that a single canister might miss. For example, if the weather changes or a window is left open, a continuous monitor catches that. In a real estate transaction or a lender testing scenario, a continuous radon monitor is often preferred because it produces a detailed report that lenders and buyers trust.

When I perform testing for Air Sense Environmental in St. Louis, we usually start with a walk-through. We check the basement slab for cracks, look at sump pumps, floor drains, and any other openings that could let radon in. Then we place detectors in the lowest occupied units, common areas like laundry rooms, and sometimes the mechanical rooms. We always follow the EPA's guidelines for radon on placement: detectors should be at least 20 inches off the floor, away from drafts, and away from exterior walls. We also make sure tenants understand not to disturb the devices.

Interpreting Results and Next Steps

Once the test is complete, the lab sends back a report. If the levels are below 4 pCi/L, you are in good shape. But if they are above that threshold, you need to take action. That is where radon mitigation comes in. The most common method for apartments is sub-slab depressurization. This involves drilling a small hole through the basement slab, installing a pipe, and attaching a fan that pulls radon from beneath the slab and vents it outside. It is effective and usually does not disrupt tenants if done correctly.

I have seen buildings where the initial test showed 8 or 10 pCi/L, and after mitigation, the levels dropped to well below 2 pCi/L. That is a significant reduction in health risk. The cost of mitigation varies, but it is far less than the potential legal and health costs of doing nothing.

One thing I always tell property managers: do not rely on a single short-term test for a final decision. Radon levels fluctuate seasonally. A short-term test is a good first step, but if you are making a long-term investment, consider a long-term test or at least do two short-term tests in different seasons. The EPA recommends testing in the winter when windows are closed and radon tends to build up. But that is not always practical for a busy apartment building. A continuous radon monitor can give you a reliable reading in just 48 hours, which helps when you need results quickly for a real estate transaction or a lender testing requirement.

Practical Advice for Property Owners

If you own or manage apartments in St. Louis, here is my advice:

Start with a discrete radon test on the ground floor and any basement units. You do not need to test every unit, but sample enough to cover different areas of the building.
Hire a licensed radon professional. In Missouri, there is no state licensing requirement, but a professional will have the right equipment and know how to interpret results. Companies like Air Sense Environmental have experience with multifamily buildings and understand HUD and lender requirements.
If you find elevated levels, do not panic. Mitigation is well understood and usually straightforward. Get quotes from two or three contractors who specialize in radon mitigation.
Keep records. If you ever sell the building or refinance, having a radon test report from a reputable company can smooth the transaction. Some lenders now require a radon test as part of their due diligence.

I have also seen cases where a property owner tried to save money by using a home test kit from a hardware store. Those kits are fine for a homeowner, but for an apartment building, they often produce unreliable results. The instructions are written for a single-family home, and placement can be tricky in a shared building. Plus, if you need the test to satisfy a lender or HUD, you need a certified professional to perform it.

The Bottom Line

Radon is a hidden hazard, but it is one you can manage with the right approach. Radon testing apartments in St. Louis is not just about compliance. It is about protecting the people who live in your buildings and protecting your investment. I have seen too many property owners wait until a tenant complains or a buyer demands a test. By then, you are reacting instead of leading.

Take the time to understand the radon risk in your building. Work with a professional who knows multifamily housing. And remember, a test is just the first step. If you need mitigation, do it right the first time. Your tenants will thank you, and your property will hold its value better in the long run.

If you have questions about specific testing methods or what the EPA guidelines mean for your building, I encourage you to reach out to a local expert. The St. Louis area has qualified professionals who can help you navigate the process from start to finish.