Phudradontestingfacts.publishlane.com
←Back

Navigating HUD Radon Testing for Commercial and Multifamily Properties

If you own or manage a commercial or multifamily property in St. Louis, you have probably heard about radon testing requirements tied to HUD loans, FHA loans, or USDA Rural Development financing. What many property owners do not realize is how much the process differs from a typical home inspection. HUD radon testing is not a simple pass-fail checkbox. It involves specific protocols, equipment, and timing that can make or break a closing date. I have seen too many deals stall because someone assumed a short-term radon test would be enough, or because the testing company did not understand HUD requirements.

Let me walk through what HUD radon testing actually entails for commercial and multifamily buildings, why it matters, and how to avoid the common pitfalls that trip up property owners and lenders alike.

Why HUD Radon Testing Exists

Radon is a radioactive gas that comes from the natural breakdown of uranium in soil. It can seep into buildings through cracks in slabs, gaps around pipes, and other openings in the foundation. The EPA has set an action level of 4 picocuries per liter of air. Above that level, the EPA recommends radon mitigation to reduce health risks. For properties financed through HUD, FHA loans, or USDA Rural Development, radon testing is typically required before closing. The goal is to ensure that the property is safe for occupants and that the lender's investment is protected from future liability.

But here is where it gets tricky: HUD requirements are not uniform across all programs. Some loans mandate testing only in areas with elevated radon potential, while others require it regardless of location. St. Louis County, for example, is in EPA Zone 1, meaning it has the highest potential for radon levels above the action level. That means almost any property in the county that goes through a HUD-backed loan will need testing.

What Makes HUD Radon Testing Different

HUD radon testing is more rigorous than a typical residential test. For one thing, the testing period must be at least 48 hours, and the test device must be placed in the lowest livable area of the building. In a multifamily property, that often means the basement or a ground-floor unit. The test cannot be disturbed during that period, so you cannot open windows, run exhaust fans, or operate HVAC systems in ways that would dilute the air. That is harder to control in a commercial setting where tenants come and go.

Another difference is the type of equipment allowed. HUD accepts both short-term radon tests and long-term radon tests, but the short-term option is more common because it fits into the typical closing timeline. However, short-term tests are more sensitive to weather and ventilation changes. A heavy rainstorm or a sudden drop in barometric pressure can cause radon levels to spike temporarily, leading to a false high reading. That is why I always recommend using a continuous radon monitor, or CRM, for HUD radon testing. Devices like the Radalink continuous radon monitor or the Airthings CRM give hour-by-hour readings and can detect tampering or placement issues. They are more expensive than a charcoal canister or an activated carbon filter test, but they provide data that holds up under scrutiny from lenders and the Missouri Department of Health.

The Role of Radon Mitigation in HUD Transactions

If the test comes back at or above 4 pCi/L, the property will need radon mitigation before the loan can close. This is where many property owners get blindsided. Mitigation is not cheap, and it is not always straightforward in a commercial or multifamily building. The most common approach is sub-slab depressurization. That involves drilling a hole through the concrete slab, creating a suction point under the foundation, and installing a radon fan that pulls the gas out before it can enter the building. The fan vents to a safe location above the roofline. This is often referred to as soil suction. A manometer is installed on the pipe to show that the system is working.

In some buildings, a passive radon system can be installed during new construction. Passive systems rely on natural convection to draw radon out, without a fan. But for existing buildings, passive systems rarely reduce radon levels enough to pass HUD requirements. You almost always need an active system with a fan. I have seen property owners try to save money by installing a passive radon system, only to fail the post-mitigation test and have to pay for a fan installation anyway. That is a costly mistake.

Practical Planning for Property Owners

If you are selling or refinancing a commercial or multifamily property through a HUD-backed loan, start the radon testing process early. Do not wait until the week before closing. Here are a few things to keep in mind:

  • Hire a testing company that is certified by the state or by a national radon proficiency program. In Missouri, the Missouri Department of Health maintains a list of approved testers.
  • Ask specifically for a continuous radon monitor. A CRM gives you a digital record of the test, which is harder to dispute than a charcoal test.
  • Plan for at least 48 hours of closed-building conditions. Coordinate with tenants to avoid opening windows or running exhaust fans during the test.
  • If the property has a sump pump, a floor drain, or a crawl space, those areas may need separate testing. HUD requirements often demand testing in every ground-contact space that is accessible.
  • If mitigation is needed, budget for sub-slab depressurization with a radon fan and a manometer. Do not assume a passive radon system will work.

Long-Term Considerations

Even after closing, radon levels can change. Soil shifts, foundation cracks develop, and new construction nearby can alter the gas flow. I recommend installing a continuous radon monitor in the basement or lowest livable area as a permanent fixture. Many modern CRMs connect to Wi-Fi and send alerts if levels rise. That kind of ongoing monitoring can save you from future liability and from having to redo HUD radon testing if you ever refinance.

Some property owners also look into radon-resistant construction when renovating. That means installing a vapor barrier under the slab, sealing all foundation openings, and including a sub-slab depressurization pipe stub that can be connected to a fan later if needed. Radon-resistant construction is not a substitute for testing, but it makes future mitigation much easier and cheaper.

Common Misconceptions

One misconception I hear often is that radon testing is only for residential properties. That is not true. HUD radon testing applies to multifamily buildings with five or more units, as well as commercial properties used for childcare, education, or healthcare. Another myth is that radon is only a problem in basements. Radon can enter through any slab-on-grade foundation, including ground-floor slabs in buildings without basements. I have tested strip malls and office buildings where the highest radon levels were in first-floor storage rooms.

Some property owners also think that if the test comes back low once, they are done forever. But HUD requirements for FHA loans and USDA Rural Development loans typically require a new test before each transaction. If you have a continuous radon monitor already installed, you can often use the data from the previous year to satisfy that requirement, but you need to check with the lender first.

Working with a Qualified Tester

The biggest piece of advice I can give is to work with a tester who understands HUD requirements. Not every radon testing company knows the difference between a HUD test and a routine real estate test. A good tester will arrive with a Radalink or Airthings CRM, place it in the correct location, log the start time and conditions, and provide a detailed report that includes the closed-building verification. They will also know how to handle borderline results. For example, if the test shows 3.9 pCi/L, a single short-term test may not be reliable. A long-term radon test over 90 days gives a more accurate annual average. HUD allows long-term tests in some cases, but it depends on the program.

In St. Louis County, where radon potential is high, I strongly recommend using a company that specializes in commercial and multifamily testing. Air Sense Environmental is one example of a local provider that focuses on this niche. They understand the nuances of HUD radon testing and can coordinate with lenders and the Missouri Department of Health if issues arise. That kind of expertise is worth paying for, because a failed test or a delayed closing costs much more than the testing fee.

Final Thoughts

HUD radon testing does not have to be a headache, but it does require planning and the right approach. If you treat it as a last-minute step, you are asking for trouble. Start early, use the right equipment, and budget for mitigation if needed. A continuous radon monitor gives you the best chance of a clean test and a smooth closing. And remember, radon mitigation is not a failure. It is a standard fix that makes the property safer and more valuable in the long run.