Why Radon Measurement Matters for Commercial and Multifamily Properties

Understanding the Hidden Risk in Your Building

For years, the conversation around radon focused almost exclusively on single-family homes. Homeowners were told to test their basements, seal cracks, and install mitigation systems. But as a professional who has worked on dozens of commercial and multifamily projects in St. Louis, I can tell you that the risk is just as real in larger buildings. The difference is that the path to finding and fixing the problem is often more complex. That is where proper radon measurement becomes critical.

Radon is a radioactive gas that comes from the natural decay of uranium in soil and rock. It moves up through the ground and can enter any building through gaps in the foundation, around pipes, or through cracks in slabs. In a commercial building or a multifamily housing complex, the sheer size of the footprint means more entry points and more potential for radon to accumulate. The EPA has set an action level of 4 picocuries per liter of air, but levels below that can still pose a long-term health risk. The only way to know what you are dealing with is through accurate radon measurement.

How Radon Testing Differs in Larger Buildings

When you are responsible for a commercial property or a multifamily building, you cannot just place a single test canister in the basement and call it done. The dynamics of air movement, the number of floors, and the variety of uses across the building all affect how radon gas behaves. I have seen cases where the ground floor had elevated radon levels while the upper floors were fine, and other cases where a ventilation system actually pulled radon from the soil into upper-level spaces. That is why a thorough radon measurement plan must account for the building's layout and mechanical systems.

Short-term tests are the most common starting point. They usually last between two and seven days and give a quick snapshot of radon levels. These are useful for initial screening or when you need results quickly for a real estate transaction or lender testing. But short-term tests can be influenced by weather, building operation, and even how the occupants use the space. A short-term test taken during a week of heavy rain might show higher levels than a dry week. That is why many experts, including the team at Air Sense Environmental, recommend following up with long-term tests whenever possible. Long-term tests run for at least three months and give a much more reliable average of radon levels over time.

For properties that need the highest level of accuracy, especially when HUD or lender testing is involved, continuous radon monitors are the tool of choice. These electronic devices record radon levels hour by hour and can detect short spikes or patterns that passive tests might miss. They also reduce the chance of tampering or error because they log data continuously. I have used continuous radon monitors in multifamily housing projects where each unit needed its own assessment, and the data they provided helped us target mitigation efforts precisely.

Radon Measurement and Building Code Compliance

In St. Louis, as in many parts of the country, building code requirements for radon are becoming more common. Some municipalities now require radon testing before a certificate of occupancy is issued for new construction or major renovations. This is especially true for commercial buildings and multifamily housing that receive federal funding or are part of HUD programs. The goal is to protect occupants before they move in, rather than discovering a problem years later.

Meeting these requirements means working with a certified professional who understands both the science of radon measurement and the local regulations. It is not enough to just buy a test kit from a hardware store and hope for the best. The placement of the test device, the duration of the test, and the conditions during testing all affect the validity of the results. A failed test can delay a project or cost thousands in unnecessary mitigation work. A properly conducted test, on the other hand, gives you the confidence that your building is safe and compliant.

When Elevated Levels Are Found: Mitigation Options

If radon measurement reveals levels above the EPA action level, the next step is mitigation. The approach depends on the building's construction and the source of the radon. In many commercial and multifamily buildings, the most effective solution is sub-slab depressurization. This involves creating a vacuum beneath the concrete slab that draws soil gas away from the building and vents it safely above the roof. It is the same principle used in homes, but the scale is much larger and requires careful engineering to ensure even coverage across the entire footprint.

Sealants also play a role. Cracks in the foundation, gaps around utility penetrations, and joints between walls and floors can all be sealed to reduce the pathways for radon entry. But sealants alone are rarely enough, especially in buildings with expansive slabs or complex foundations. They work best as part of a system that includes active soil depressurization.

In some buildings, the existing ventilation system can be modified to help control radon levels. Increasing the air exchange rate in basement or ground-floor spaces can dilute radon concentrations, but this approach must be balanced with energy costs and comfort. It is not a substitute for source removal, but it can be a useful supplement. The key is to have a professional evaluate the building and design a mitigation strategy that fits the specific conditions.

Why Professional Radon Measurement Matters

I have been in buildings where the owners thought they were fine because they had tested once five years ago. But radon levels can change over time due to shifts in the soil, changes in the building structure, or even new construction nearby. Regular radon measurement is the only way to stay on top of the risk. For commercial buildings and multifamily housing, where dozens or hundreds of people may spend their days, the stakes are even higher.

Professional radon measurement also provides documentation that can be important for liability and compliance. If a tenant or employee raises concerns about radon, having a record of recent testing and mitigation work shows that you take the issue seriously. It can also be a requirement for obtaining financing or insurance on certain types of properties. Lenders and HUD often require testing as part of their due diligence, and they expect the results to come from a reliable source using approved methods.

Practical Steps for Property Owners and Managers

If you manage a commercial building or a multifamily complex in St. Louis, here are some practical steps to consider:

Start with a baseline radon measurement using short-term tests placed according to EPA guidelines. Test on every floor that has contact with the soil or is below the third floor.
If initial results are near or above the action level, follow up with long-term tests or continuous radon monitors to get a more accurate picture of average radon levels.
Work with a certified radon professional, like those at Air Sense Environmental, who has experience with commercial and multifamily properties. They can help you design a testing plan that meets your specific needs, whether it is for HUD, lender testing, or general occupant safety.
If mitigation is needed, consider sub-slab depressurization as the primary solution, supplemented with sealants and ventilation adjustments as needed.
Re-test after any major renovation or change to the building's foundation or HVAC system, and at least every two years as a general rule.

Final Thoughts on Radon Measurement

Radon is a silent hazard, but it does not have to be a mystery. With the right approach to radon measurement, you can identify problems early and take effective action. Whether you are dealing with a single commercial building or a large multifamily housing complex, the principles are the same: test thoroughly, understand the data, and address the source. St. Louis has its own geological characteristics that influence radon potential, so working with local experts who know the area adds another layer of confidence. The investment in proper testing and mitigation is small compared to the health and legal risks of doing nothing. And with the right partner, the process is straightforward and manageable.