Commercial Radon Testing: How Buildings Are Tested

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Radon does not stop at the property line between homes and businesses. The same soil gas that seeps into a basement can move into an office on a slab, a ground-floor retail unit, a school classroom or the lower floors of an apartment building. What changes is the testing. A house can often be screened with one or two detectors in the lowest lived-in level, but a larger building has many rooms, several foundation types, mechanical systems that push and pull air, and occupants who are present only during certain hours. This guide explains how commercial radon testing differs from home testing, which rooms usually get tested, how continuous monitors and passive devices fit in, what schools should know and what happens after a high result. It draws on EPA and CDC material available in 2026 and is general information, not a protocol for any specific building. A qualified radon measurement professional should design the plan for a particular property.

Part of our Radon Levels guide — start there for the full picture →

What Commercial Radon Testing Involves

Commercial radon testing is the measurement of radon in nonresidential and larger shared buildings: offices, retail, warehouses with occupied areas, schools, daycare centers, medical offices, hotels and multifamily housing. The basic science is the same as in a house. Radon is a radioactive gas from the natural breakdown of uranium in soil and rock, and it enters through cracks, joints, utility penetrations and other openings in contact with the ground. CDC notes that radon is the second leading cause of lung cancer deaths in the United States after cigarette smoke, and its guidance lists testing a home or office among the steps to measure and reduce radon levels.

The difference is scale and complexity. A commercial test plan usually answers questions a homeowner rarely needs to ask:

• Which rooms are in contact with the ground, and which are frequently occupied?
• How many detectors are needed so that every relevant room is covered?
• How does the HVAC system operate during the test, and does it match normal occupied conditions?
• Are results needed for a sale, a lender, a lease, a school policy or occupant health?
• Who will review the results and decide on follow-up testing or mitigation?

The radon testing guide and the radon levels hub cover the basics of how radon behaves and what the numbers mean, which is useful context before planning a larger building.

Why Commercial Buildings Need Radon Testing

The health case for testing a workplace or school is the same as for a home. CDC states that the EPA and the Surgeon General’s office estimate radon is responsible for more than 21,000 lung cancer deaths each year in the United States, and it explains that radioactive particles from the decay of radon gas can get trapped in the lungs when radon is breathed in. CDC also notes that the only way to know if a home or office has unsafe levels of radon is by testing.

Beyond health, there are practical reasons owners order commercial radon testing:

• Transactions and financing. Some lenders and buyers ask for radon results on multifamily and commercial properties as part of due diligence.
• Leases and tenant questions. Tenants, employees and parents increasingly ask about indoor air, and a recent test result gives a clear answer.
• Renovations and HVAC changes. New slabs, additions, sealed windows or changed ventilation can shift radon levels, so a test before and after major work is useful.
• Policy and program requirements. Some states, school programs and housing programs set testing expectations for certain building types.

How Commercial Testing Differs From Home Testing

Many rooms, not one location

Radon levels can vary sharply from room to room in a large building. One office over a crack in the slab or near a utility trench may read far higher than its neighbor. A single detector in a hallway can miss a high room entirely. Commercial plans therefore usually place detectors in every frequently occupied room that is in contact with the ground, and often in a sample of rooms on the floor above.

Ground-contact rooms and lower floors

Rooms built on slabs, over crawl spaces, or partly below grade are the priority. In multistory buildings, upper floors are generally lower risk, though elevator shafts, stairwells, chases and HVAC returns can carry soil gas upward. A test plan may include upper-floor rooms when the building has features that could move air between levels.

HVAC operating conditions

The heating, ventilation and air-conditioning system has a large effect on indoor radon. Systems that bring in outdoor air can dilute radon during occupied hours, while setbacks at night or on weekends can let it build up. Exhaust-heavy systems can depressurize a building and draw in more soil gas. Commercial tests are usually run with the HVAC system operating as it normally does when the building is occupied, and some protocols call for documenting system schedules. A test run during an unusual shutdown, or with doors propped open for a renovation, may not reflect normal exposure.

Published protocols

Consensus standards bodies in the radon industry have published measurement protocols specifically for multifamily, school, commercial and mixed-use buildings. These cover detector placement, the number of rooms to test, quality control such as duplicate detectors and blanks, and how to handle large open areas. A measurement professional working on a commercial building typically follows one of these protocols, and some states or lenders may require a specific one. Asking which protocol a provider uses is a simple way to check that the plan is built for the building type.

Occupancy patterns

People in a house can be exposed day and night, while offices and schools are mostly occupied during the day. Continuous monitors can show how levels change across the day and week, which helps decide whether a high average reflects occupied hours or mainly nights and weekends. That information can shape both mitigation design and HVAC adjustments.

Testing Approach by Building Type

The table below summarizes common approaches by building type. It is a general overview, and the actual plan depends on the protocol used, the building layout, local requirements and the purpose of the test.

For apartment-specific questions, including how tenants and owners can approach testing, see the guide to radon in apartments.

Radon Testing in Schools

Schools get special attention because children spend many hours there and may be more sensitive to radiation. EPA’s radon in schools page states that “The EPA recommends that all schools nationwide be tested for radon.” It also reports that “A nationwide survey of radon levels in schools estimates that nearly one in five has at least one schoolroom with a short-term radon level above the action level of 4 pCi/L (picocuries per liter).”

The same page lists the basic elements of testing a school: test all frequently used rooms on and below the ground level, conduct tests in the cooler months of the year, and follow the testing strategy EPA describes. It notes that testing for radon is simple and relatively inexpensive, and it points schools to their State Radon Office for more information.

For a school district, that usually means planning the work across a whole building inventory: identifying every classroom, office, gym, cafeteria and library on or below ground level, scheduling tests when buildings are operating normally, and setting a policy for retesting after renovations or HVAC changes. Parents and staff often ask for results, so many districts plan communication alongside the testing itself.

Continuous Monitors Versus Passive Devices

Commercial testing uses the same broad device families as home testing, but the choice between them matters more when dozens of rooms are involved.

Passive devices

Passive devices include charcoal canisters, alpha-track detectors and electret ion chambers. They do not need power, are relatively inexpensive per room and can be deployed in large numbers. After the test period, they go to a laboratory for analysis. EPA’s Citizen’s Guide notes that short-term tests remain in place for two days to 90 days, depending on the device, and lists these devices among those most commonly used for short-term testing. Passive devices report an average over the test period, without showing how levels changed hour by hour.

Continuous radon monitors

Continuous monitors are powered electronic instruments that record radon levels at regular intervals, often hourly. They show patterns across occupied and unoccupied hours, can reveal the effect of HVAC schedules, and often include tamper indicators that matter in transactions. They cost more per unit, so commercial plans sometimes use them in a subset of rooms or for follow-up testing where passive results were high. Device types and features are compared in the radon monitor guide.

Short-term versus long-term

EPA’s Citizen’s Guide describes short-term tests as the quickest way to test and notes that, because radon levels tend to vary from day to day and season to season, a long-term test is more likely to reflect a building’s year-round average. In commercial practice, short-term tests are often used for initial screening and transactions, and long-term or repeated tests are used to confirm results or verify mitigation. Typical durations are covered in the radon test time guide.

What Happens After a High Result

EPA’s Citizen’s Guide recommends fixing a home if the radon level is 4 pCi/L or higher, and adds that radon levels less than 4 pCi/L still pose a risk and in many cases may be reduced. Commercial owners and school districts commonly use the same 4 pCi/L action level as a reference point, though some states, lenders or programs apply their own requirements. Results and their meaning are summarized in the radon levels chart.

A typical sequence after a high initial result looks like this:

1. Confirm the result. Follow-up testing, often with a continuous monitor or a longer test, checks that the reading reflects normal conditions.
2. Look at HVAC operation. Ventilation changes can lower levels in some rooms, though they are rarely a full solution on their own.
3. Diagnose the building. A mitigation professional checks the slab, sub-slab material, utility trenches and pressure differences to design a system.
4. Install mitigation. Larger buildings often need sub-slab depressurization with several suction points and fans, sealing of major entry points, and sometimes HVAC adjustments.
5. Retest after mitigation. Post-mitigation testing confirms the system works, and periodic retesting keeps it on track.

The design side of this work is covered in the guides to radon mitigation for commercial buildings and commercial radon mitigation systems.

Choosing a Commercial Radon Testing Provider

Not every residential radon tester is set up for larger buildings. When comparing providers, it helps to ask:

• Which measurement protocol will be followed for this building type?
• How many rooms will be tested, and how were they chosen?
• What devices will be used, and will any continuous monitors be included?
• How will HVAC operation be documented during the test?
• What quality control is included, such as duplicate detectors or blanks?
• Does the provider hold the credentials or state licensing that applies locally?
• What does the final report include, and how soon will it arrive?

A clear written test plan before work starts makes it easier to compare quotes. More detail on vetting providers is in the commercial radon testing company guide.

Planning a Commercial Test: A Practical Checklist

Good results start with planning. Before detectors go out, a measurement professional and the building owner or manager usually work through a checklist like this:

1. Gather floor plans. Mark every room in contact with the ground, including slabs, crawl spaces and below-grade areas.
2. Build a room inventory. Note which rooms are frequently occupied, which are storage or mechanical, and which have unusual features such as sumps, floor drains or utility trenches.
3. Document the HVAC system. Record how many air handlers serve the ground floor, their schedules, outdoor air settings and any setbacks at night or on weekends.
4. Set test conditions. Many protocols ask for closed-building conditions, meaning exterior doors and windows kept closed except for normal entry and exit, for a period before and during short-term tests.
5. Notify occupants. Staff, tenants or custodians should know not to move, unplug or cover detectors, and why the doors should stay closed.
6. Place detectors carefully. Detectors generally go at breathing height, away from exterior walls, drafts, heat sources, direct sunlight and high humidity, following the protocol and device instructions.
7. Add quality control. Duplicate detectors and blanks help confirm results are reliable, especially in larger buildings.
8. Keep chain of custody. Records of placement times, retrieval times and handling support the report if results are questioned.

Owners who are also checking for moisture or mold problems sometimes schedule both assessments together, as described in the guide to mold and radon testing.

Common Mistakes in Commercial Radon Testing

• Testing only one location. A single detector in a lobby or hallway says little about individual offices or classrooms.
• Skipping ground-contact storage areas that are actually used. A “storage room” that doubles as a workspace is an occupied room.
• Testing with HVAC off or unusual. A shutdown, a holiday setback or a renovation can push results up or down.
• Ignoring upper floors with air pathways. Shafts and chases can carry radon above the ground floor.
• Treating one low result as permanent. Renovations, HVAC changes and settling can change levels over time, so retesting is part of the plan.
• Losing the paperwork. Without placement records and a clear report, results may need to be repeated for a sale or audit.

Cost and Timing

Commercial radon testing costs depend mostly on the number of rooms tested, the device types, the protocol, travel and reporting requirements. A small office with a few ground-contact rooms may cost only somewhat more than a home test, while a school district or large multifamily property can involve hundreds of detectors and a detailed report. Continuous monitors usually raise the cost per room compared with passive devices. Pricing patterns for different situations are in the radon test cost guide.

Timing matters too. Short-term tests often run for a few days, plus lab or download time, so a commercial transaction should allow room in the schedule for testing, a possible retest and a mitigation quote. Testing in cooler months, when buildings are more closed up, tends to give a more conservative picture, which is one reason EPA suggests that timing for schools.

Commercial Radon Testing in Colorado

Colorado is widely considered a higher-radon state, and much of the Front Range sits on geology that can produce elevated indoor radon. That does not mean every building will test high, and neighboring buildings can read very differently. It does mean that owners, property managers and schools along the Front Range, from Fort Collins through Denver to Colorado Springs, have good reason to test rather than assume. Local requirements for schools, childcare facilities, rentals and real estate transactions vary and can change, so checking with the state radon program or a local professional is the best way to confirm current rules. Area-level patterns can be explored in the guide to radon levels by ZIP code in Colorado, keeping in mind that only a test measures an individual building.

New commercial construction is worth a note as well. Building a new office, school or apartment project on Front Range soil does not guarantee low radon, and installing passive soil-gas control features during construction is generally far cheaper than retrofitting later. Even with those features in place, testing after occupancy is the only way to confirm the result, and a passive system can usually be upgraded with a fan if levels come back high. Owners of older buildings that have changed use, such as a warehouse converted to offices or a former retail space turned into a clinic, should treat the new layout as a reason to test again.

References

• Radon in Schools — U.S. Environmental Protection Agency
• A Citizen’s Guide to Radon (2016) — U.S. Environmental Protection Agency
• About Radon — Centers for Disease Control and Prevention

Managing a building on the Front Range and unsure where to start with radon? Drop us a line with the building type and size, and we can talk through a sensible testing plan.

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We may earn commission from links on this page. Lead-form submissions are forwarded to local inspector partners. How we research and review.