What Property Managers Should Know About HUD Radon Testing Requirements

If you manage or own multifamily housing in St. Louis, you have probably heard about radon. It is a radioactive gas that comes from the natural decay of uranium in soil. It seeps into buildings through cracks in the foundation, gaps around pipes, and other openings. The problem is that you cannot see it, smell it, or taste it. The only way to know if a building has a radon problem is to test for it. And when a property is involved in a HUD transaction, HUD radon testing becomes a specific requirement that cannot be ignored.

I have spent years working with commercial and multifamily properties in the St. Louis area, and I can tell you that radon testing is not a one-size-fits-all process. HUD has its own set of rules, and those rules differ from what the EPA recommends for a typical home. For property managers who are used to residential testing, the shift to HUD radon testing can feel like learning a new language. But it is straightforward once you understand the key differences.

Why HUD Radon Testing Exists

HUD requires radon testing for any property that uses FHA loan programs or involves HUD-insured financing. This includes multifamily buildings, assisted living facilities, and some single-family rentals. The reason is simple: radon exposure is the second leading cause of lung cancer after smoking. HUD wants to protect tenants and borrowers. If a property has elevated radon levels, HUD requires mitigation before the loan closes or before tenants move in.

Let me give you a real example. I worked with a property manager in St. Louis County who was refinancing a 12-unit building through an FHA loan. The lender required radon testing as part of the due diligence. The manager assumed a short-term radon test placed in the basement would be enough. But HUD requirements are more detailed. They specify where to place the monitors, how many to use, and how long to test. The property manager had to redo the testing twice before it met HUD standards. That cost time and money.

What HUD Radon Testing Requires

HUD radon testing is based on EPA protocols but with some important additions. The first thing to know is that HUD requires testing in all occupied ground-level spaces. That means every unit on the ground floor, plus any common areas like laundry rooms, community rooms, and offices. If a building has a basement that is used as living space, that basement must be tested too.

The testing period is usually a minimum of 48 hours, but HUD prefers a longer test when possible. A short-term radon test using an activated carbon filter or a continuous radon monitor (CRM) is acceptable as long as it is placed correctly. A continuous radon monitor is often a better choice because it records readings over time and cannot be tampered with. Devices like Radalink or Airthings are common in the industry. They give you a digital readout and a data log that satisfies the documentation HUD expects.

One detail that trips people up is that HUD requires testing during the heating season or under closed-building conditions. That means all windows and doors must stay closed for at least 12 hours before the test starts and for the entire testing period. This is not always easy in a multifamily building where tenants want fresh air. But it is a non-negotiable part of the HUD radon testing protocol. If you open a window for even an hour, the test result may be invalid.

Testing for Different Loan Programs

HUD radon testing is not the only program that requires radon checks. USDA Rural Development and some conventional lenders also have radon testing requirements. USDA Rural Development follows similar protocols to HUD, but their focus is on rural properties. I have seen cases where a property needed to satisfy both HUD requirements and a separate lender’s radon policy. That can be frustrating because the requirements do not always align perfectly. In those cases, it pays to use a testing company that knows the differences.

The Missouri Department of Health offers guidance on radon testing and mitigation, but they do not enforce HUD rules. That is left to the lender or the HUD field office. So if you are working with a lender who is not familiar with HUD radon testing, you may have to educate them. I have had to send lenders copies of HUD Handbook 4000.1 just to prove that the testing I performed meets their requirements.

What Happens When Radon Levels Are High

If a test shows radon levels at or above the EPA action level of 4.0 pCi/L, the next step is radon mitigation. For a multifamily building, the most common method is sub-slab depressurization. This involves drilling a hole through the concrete floor, running a pipe down into the soil, and attaching a radon fan that pulls the gas from under the building and vents it safely above the roofline. A manometer is installed on the system to show that it is working. The manometer is a simple U-shaped tube with colored fluid that indicates whether the fan is creating enough suction.

Sometimes a passive radon system is already in place. A passive system uses natural air pressure differences to draw radon out, without a fan. But passive systems often do not reduce radon enough to meet the EPA action level. In those cases, a radon fan is added to convert the passive system into an active one. This is called soil suction, and it is the most reliable method for reducing radon in a concrete slab building.

I once consulted on a 40-unit building in St. Louis County where the initial HUD radon testing showed levels above 6 pCi/L in three ground-floor units. The building had a passive radon system that was installed during construction, but it was not working well. The manometer showed no fluid movement, meaning the system was not pulling any soil gas. We installed a radon fan on each of the three passive vents and retested. The levels dropped below 2 pCi/L within 48 hours. That property was able to close its FHA loan without further delay.

Mitigation and Construction Considerations

For new construction, radon-resistant construction techniques can prevent problems before they start. This includes placing a layer of gravel under the slab, a vapor barrier, and a sealed sump with a pipe stub that can later be connected to a radon fan if needed. Many builders in St. Louis now include a passive radon system as standard, but not all do. If you are building a multifamily property that will eventually use HUD financing, it is wise to include radon-resistant construction from the beginning. Retrofitting a sub-slab depressurization system later is more expensive and disruptive.

One thing I want to emphasize: radon mitigation is not a one-time fix. After a system is installed, it must be maintained. The radon fan has a lifespan of about five to ten years. The manometer should be checked periodically to confirm the system is still running. And the building should be retested every two years or whenever there is a major renovation that could affect airflow.

Practical Advice for Property Managers

If you are preparing for HUD radon testing, here are a few things to keep in mind:

• Start the testing process early. Do not wait until the week before closing. If levels are high, you need time to install mitigation and retest.
• Use a certified radon measurement professional. Many lenders will accept test results from any certified tester, but some have their own approved list. Ask before you test.
• Keep records of every test, including the monitor placement log, the closed-building conditions, and the lab results. HUD may request this documentation years later.

HUD radon testing is not just a box to check. It is a real protection for the people who live and work in your building. And for property managers who understand the process, it is something that can be handled smoothly and without surprises. The key is to know the rules, use the right equipment, and work with someone who has done it before.

In St. Louis County and the surrounding area, radon levels vary block by block. I have tested buildings that were completely clean and others that needed major mitigation. There is no substitute for actual testing. If you rely on a neighbor’s test result or a county map, you are taking a risk. The only way to know your building’s radon level is to test it yourself, using a method that meets HUD requirements.

Whether you are refinancing with an FHA loan, applying for USDA Rural Development funding, or just want to keep your tenants safe, proper radon testing is the first step. And if you are dealing with HUD, make sure the testing you do is the testing they expect. It will save you time, money, and a lot of frustration.