Why Radon Testing for Businesses Matters More Than You Think

When I started in this field, most calls came from homeowners who had just read a news article or received a test kit from a hardware store. Commercial property owners and property managers were a different story. They rarely called unless a lender or a tenant demanded it. That has changed in the last decade. Today, more business owners and investors understand that radon testing for businesses is not a nice-to-have. It is a due diligence step that protects health, property value, and legal standing.

I have walked through basements of multifamily properties in St. Louis where the readings made everyone pause. I have also seen brand-new office buildings that tested fine. The difference is not about age or location. It is about whether anyone ever bothered to check. Radon is a radioactive gas that comes from the natural decay of uranium in soil. It moves up through the ground and enters buildings through cracks, sump pumps, utility openings, and gaps around pipes. You cannot see it, smell it, or taste it. The only way to know if it is present is to test.

Why Commercial Properties Are Different

Radon testing for businesses is not the same as testing a single-family home. A commercial building has different ventilation systems, occupancy patterns, and floor layouts. A multifamily property has shared spaces, multiple units, and common areas that all need attention. The stakes are higher because more people are exposed. Tenants, employees, and visitors spend hours each day inside those walls. If radon levels are high, the liability falls on the building owner.

I have seen cases where a property owner ignored radon for years and then faced a costly retrofit because a real estate transaction required a test. Fannie Mae and HUD both have guidelines that often mandate radon testing for certain loans. When a property is being sold or refinanced, a failed test can delay the closing or force the seller to install a radon mitigation system at the last minute. That is a stressful and expensive way to discover a problem.

Testing Methods and What They Tell You

There are two main approaches to radon testing: short-term and long-term. A short-term radon test typically lasts between two and seven days. It gives you a quick snapshot. This is the most common method used during a real estate transaction because the timeline is tight. A long-term radon test runs for at least 90 days. It provides a more accurate picture of the average radon level over time because radon concentrations can fluctuate with weather, ventilation, and occupancy.

Within those categories, you have choices in hardware. A passive radon monitor is a small device that you place in the building and send to a lab for analysis. It is simple and cost-effective, but you have to wait for results. A continuous radon monitor, also called a CRM, gives you hourly readings and can detect short-term spikes. That real-time data is useful for troubleshooting or for verifying that a radon mitigation system is working properly. Both methods have their place, and the right choice depends on the situation.

I have used all of these tools over the years. In St. Louis, where soil conditions vary block by block, I often recommend a combination approach. Start with a short-term test using a CRM to get baseline data. If the results are borderline, follow up with a long-term test using passive monitors. That saves time and money while still giving you reliable information.

Standards and Credentials Matter

Not all radon testing is done to the same standard. The EPA has published protocols for testing and mitigation, but the actual implementation depends on who is doing the work. ANSI standards provide another layer of guidance, especially for multifamily properties. When you hire a tester, you want someone who is certified by the National Radon Proficiency Program, or NRPP. That certification means the person has passed an exam, follows a code of ethics, and stays current with industry practices.

I have seen tests performed by uncertified individuals who placed monitors in the wrong locations or left them in place for the wrong duration. The results were useless. In one case, a property manager had to redo the entire testing process because the initial test did not meet HUD requirements. That cost time and money that could have been avoided with a qualified professional from the start.

What Happens After the Test

If the test shows radon levels above the EPA action level of 4 picocuries per liter, the next step is radon reduction. The most common method for commercial buildings is sub-slab depressurization. This involves creating a suction point under the concrete slab and venting the gas above the roofline. It is a proven technique that works well in most buildings. But every building is different. The design of the system depends on the foundation type, the soil composition, and the layout of the mechanical systems.

After the radon mitigation system is installed, a post-mitigation test is necessary to confirm that the system is effective. This test should be done by the same certified professional who did the initial testing, or by another qualified tester. I have seen systems that looked good on paper but failed the post-mitigation test because of a hidden crack or a poorly sealed sump pump. The test catches those issues before they become health problems.

Radon Testing in Real Estate Transactions

If you are involved in a real estate transaction involving a commercial or multifamily property, expect radon to come up. Fannie Mae requires radon testing for certain loan types, especially for multifamily properties with five or more units. HUD has its own requirements for properties with federal housing assistance. Some lenders offer a product called LenderPlus that bundles radon testing into the loan process. If you are buying or refinancing, it is worth asking your lender what they require.

I have worked with buyers who assumed radon was not an issue because the building was newer or because they had never heard of a problem in that neighborhood. Those assumptions are risky. Radon does not follow property lines. It follows the geology. Two buildings on the same street can have very different readings. The only way to know is to test.

A Practical Example

Not long ago, I was called to a multifamily property in St. Louis that was being sold. The buyer’s lender required radon testing as part of the due diligence. The building had four units and a finished basement that the owner used as a common area. I placed continuous radon monitors in the basement and on the first floor. The basement readings came back at 6.2 picocuries per liter, well above the action level. The first floor was fine.

The seller had two options. They could install a radon mitigation system before closing, or they could negotiate a credit with the buyer. They chose to install a sub-slab depressurization system. The post-mitigation test showed levels below 2 picocuries per liter. The transaction closed on time. The buyer was relieved, and the seller avoided a last-minute deal collapse. That is the kind of outcome that proper radon testing for businesses makes possible.

Choosing a Testing Provider

When you look for a company to handle radon testing for businesses, experience matters. The provider should understand commercial and multifamily properties specifically. They should use calibrated equipment and follow EPA and ANSI protocols. They should be able to explain the results and recommend next steps. In St. Louis, Air Sense Environmental is a company that fits that description. They have been doing this work for years and know the local geology and building stock.

I am not here to pitch one company over another. But I will say this: do not hire someone who shows up with a single test kit and a vague plan. Radon testing in a commercial setting is not a DIY job. It requires professional judgment about monitor placement, building dynamics, and interpretation of results. The cost of a proper test is small compared to the cost of getting it wrong.

Final Thoughts

Radon is a serious health risk, but it is also a manageable one. The first step is testing. If you own or manage a commercial building or multifamily property, schedule a test. If you are buying or selling, make sure radon is on your checklist. The process is straightforward, and the information you get is invaluable. You cannot fix a problem you do not know about. Once you know, you can act.