Radon Mitigation in Commercial Buildings: How It Differs

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Radon behaves the same way in an office, a school or an apartment building as it does in a house: it moves out of the soil, finds openings in the foundation, and accumulates indoors. What changes in larger buildings is almost everything about the fix. Slabs are bigger and often divided by footings, mechanical systems move large volumes of air and change indoor pressure, occupants are many and varied, and a single test location says little about the whole floor plate. This guide explains how radon mitigation for commercial buildings differs from residential work, including multiple suction points, HVAC pressurization, testing protocols, schools and multifamily buildings, building-specific diagnostics, post-mitigation testing and long-term monitoring. It also covers Colorado considerations and how costs tend to scale. Figures and requirements vary by building and jurisdiction, so treat the numbers here as general context rather than quotes.

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

Why Radon Matters in Larger Buildings

Radon is a radioactive gas released naturally from rocks, soil and water. The CDC explains that it can get trapped inside homes and buildings and build up in the air, and that breathing high levels over time may cause lung cancer. The CDC describes radon as the second leading cause of lung cancer deaths in the United States after cigarette smoking, citing an EPA and Surgeon General estimate of more than 21,000 deaths a year. The CDC also notes that radon can build up in any home or building, whether it has a basement, is sealed or drafty, or is new or old, and that levels are often higher in basements and lower floors.

EPA’s Citizen’s Guide to Radon makes the same point about building type: radon can get into homes, offices and schools and produce a high indoor level. The guide recommends testing in schools and suggests asking the state radon office about radon problems in schools, daycare and childcare facilities, and workplaces. For a building owner, the practical consequence is that a commercial property with ground-contact floors carries the same physical risk as a house, while serving many more people for many hours a day.

The action level used across federal guidance is 4 pCi/L. The CDC says EPA recommends fixing a home at or above that level and adds that there is no known safe level, so lower is always better. Our radon levels chart puts common results in context, and the radon testing hub covers testing basics.

How Commercial Mitigation Differs From Residential

Residential and commercial systems use the same physics. EPA’s Consumer’s Guide to Radon Reduction describes active subslab suction, also called subslab depressurization, as the most common and usually most reliable method: suction pipes are inserted through the slab into the crushed rock or soil beneath, and a vent fan draws radon from under the building and releases it outdoors while creating negative pressure below the slab. The guide notes that the number and location of suction pipes depends on how easily air moves in the material under the slab and on the strength of the radon source, and that in a house a single suction point is often enough.

That last clause is where commercial work diverges. In a large building, one suction point is rarely enough. The reasons are structural and operational:

• Slab area. A warehouse, school wing or office floor can cover many times the footprint of a house. Pressure field extension from one point weakens with distance, especially under tight soils.
• Interior footings and grade beams. Thickened footings under load-bearing walls and columns break the slab into zones. Each zone may need its own suction point.
• Sub-slab material. Older commercial buildings may have dense fill or no gravel layer at all, which limits airflow and pushes designers toward more points or higher-vacuum fans.
• Utilities and penetrations. Elevator pits, trench drains, utility tunnels, sumps and floor drains are common radon entry routes that a typical house does not have.
• Mechanical systems. Commercial HVAC can depressurize or pressurize the lower floors depending on how exhaust and outdoor air are balanced, which changes how much soil gas is drawn in.
• Occupancy and access. Work often has to happen after hours, around tenants, and in compliance with fire-rated assemblies and building codes.

Our guides to commercial radon mitigation and the sub-slab radon mitigation system describe the hardware in more detail.

Residential vs Commercial Mitigation at a Glance

Building-Specific Diagnostics

EPA’s Consumer’s Guide describes diagnostic tests that help a contractor choose a system. One is a soil communication test, in which a vacuum is applied at one small hole in the slab while chemical smoke at a second hole shows whether air is being pulled between them. The guide explains that this helps a contractor decide whether certain systems would work well, and that the need for diagnostics depends on details such as foundation design and the material under the building. It also notes that a contractor may have concerns about backdrafting of combustion appliances and may recommend having them checked.

In commercial work, that diagnostic step usually grows into a structured investigation:

1. Document review. Foundation drawings, footing layouts, sub-slab material, utility trenches and mechanical schedules show where zones and entry routes are likely.
2. Initial testing. Measurements in occupied ground-contact rooms identify which areas exceed the action level and how widely results vary.
3. Pressure field mapping. Test holes across each zone measure how far suction from a trial point extends, which determines how many points are needed and where.
4. HVAC evaluation. Measuring pressure differences between indoor spaces and the sub-slab area during different operating modes shows whether mechanical systems are drawing soil gas in.
5. Entry route survey. Elevator pits, sumps, floor drains, slab cracks, expansion joints and utility penetrations are located and evaluated for sealing.

The result is a design built for that specific building rather than a template. Two structures of the same size can need very different systems because of differences in sub-slab material, footing layout or ventilation.

HVAC Pressurization as a Strategy

EPA’s Consumer’s Guide lists house or room pressurization among radon reduction techniques. It describes the method as using a fan to blow air into the lowest level from upstairs or outdoors to create enough pressure to keep radon from entering. The guide is candid about limits: effectiveness depends on construction, climate, appliances and occupant behavior; doors and windows on the lowest level must stay closed except for normal entry and exit; and bringing in more outdoor air can cause moisture problems and energy penalties.

In commercial buildings, the same idea is often applied through the existing air handling system. Adjusting the balance between outdoor air intake and exhaust can keep ground-contact spaces at slightly positive pressure relative to the soil, reducing soil gas entry. This approach can work well in buildings with tight envelopes and well-controlled mechanical systems, and it is often combined with sub-slab depressurization rather than used alone. The trade-offs mirror EPA’s residential caution:

• Pressure relationships change when equipment cycles, schedules change, or setpoints are adjusted, so performance can vary across nights, weekends and seasons.
• More outdoor air raises heating, cooling and dehumidification loads.
• Unbalanced exhaust in kitchens, labs, restrooms or garages can undo pressurization in nearby rooms.
• The strategy depends on ongoing control and maintenance, not a one-time installation.

For those reasons, pressurization tends to be most reliable when it is designed with the mechanical engineer, documented in the building’s operating sequences, and verified by testing under the conditions the building actually runs. A complementary radon exhaust system often provides a more stable baseline.

Testing Protocols, Schools and Multifamily Buildings

Commercial radon testing uses more locations and more structure than a single home test. National standards bodies publish measurement and mitigation protocols specifically for multifamily, school, commercial and mixed-use buildings. In general terms they call for testing frequently occupied ground-contact rooms, controlling building conditions during the test, and documenting HVAC status. State programs may adopt or reference them, so check what applies to the property.

Schools

EPA’s radon in schools page reports that a nationwide survey estimated nearly one in five schools has at least one schoolroom with a short-term radon level above 4 pCi/L, and that EPA estimates more than 70,000 schoolrooms in use have high short-term levels. EPA recommends that all schools be tested. The basic elements it lists are testing all frequently used rooms on and below ground level, conducting tests in the cooler months, and following a defined testing strategy. The page also states that if a school’s results are high, proven techniques can lower the levels.

Schools add constraints that affect mitigation: work is often scheduled during breaks, classroom unit ventilators and rooftop units vary room by room, and communicating results to parents and staff matters.

Multifamily buildings

Apartment and condominium buildings combine residential occupancy with commercial-scale construction. Ground-floor units, garden-level apartments and units above crawl spaces or garages are usually the focus. Testing typically covers a sample or all ground-contact units, and mitigation may involve several sub-slab systems serving different sections. Our guide to radon in apartments explains what tenants can ask for, and our page on commercial radon testing covers the measurement side for owners.

Test duration

EPA’s Citizen’s Guide explains the general difference between short-term tests, which stay in place for 2 to 90 days, and long-term tests of more than 90 days, which better reflect year-round averages. Commercial programs often begin with short-term screening across many rooms, then follow up where results are elevated. Our guide to radon test time covers durations in more detail.

Post-Mitigation Testing and Ongoing Monitoring

EPA’s Consumer’s Guide gives the residential baseline for verifying a system: a post-mitigation test should be done within 30 days of installation, but no sooner than 24 hours after the system starts operating with the fan on. It recommends a two- to seven-day measurement with windows and doors closed for 12 hours before and during the test, except for normal entry and exit. It also recommends an independent follow-up measurement in addition to any test by the contractor, to avoid a conflict of interest. The CDC likewise advises testing again after repairs to confirm they worked.

In a commercial building, the same principles apply across every mitigated area. Practical steps include:

• Retest each zone. A single passing result does not confirm that every suction zone is performing.
• Test under normal operation. Run HVAC as it actually operates, including night and weekend setbacks, so results reflect real conditions.
• Keep the fans running. EPA’s Consumer’s Guide stresses that an active system’s fan must run continuously.
• Watch the indicators. The guide recommends regularly checking the warning device, usually a manometer, and calling a contractor if it shows a problem. Fans may last five years or more and then need repair or replacement.
• Retest periodically. For homes, EPA suggests retesting at least every two years. Commercial owners often set a similar or tighter schedule and retest after renovations, HVAC changes or occupancy changes.
• Consider continuous monitoring. Continuous monitors in key rooms can show trends and catch a fan failure between scheduled tests. See our guide to the radon monitor for device types.
• Keep records. Logs of test results, fan status and maintenance support tenant communication, lender questions and future sales.

New Construction, Additions and Renovations

Building radon control into a new structure is far easier than retrofitting it. EPA’s Citizen’s Guide notes that radon-resistant construction techniques can be effective in preventing radon entry, and that installing them during construction makes it easier and less expensive to reduce levels further if passive features are not enough. It also recommends testing after occupancy even when a building was constructed radon-resistant, and activating a passive system with a vent fan if levels remain above 4 pCi/L. That guidance is written for homes, but the logic carries over to commercial projects.

For a larger new building, radon-resistant design generally includes a continuous gas-permeable layer under the slab, a soil gas retarder, sealed slab penetrations and joints, and vent piping that can be activated with a fan. Because footings divide the slab, designers often plan separate collection zones from the start. National standards bodies publish new-construction guidance for multifamily, school and commercial buildings, and some jurisdictions adopt radon provisions in their codes, so check local requirements early in design.

Renovations deserve the same attention. Converting a warehouse to offices, finishing a lower level, adding an elevator pit, or rebalancing an HVAC system can change radon entry and pressure relationships. EPA’s Consumer’s Guide advises retesting after remodeling, and commercial owners should treat any change to ground-contact spaces or mechanical systems as a trigger for new measurements.

Planning a Commercial Mitigation Project

A well-run project follows a predictable sequence, and organizing it this way helps owners compare contractors and keep occupants informed.

1. Confirm the problem. Review initial test results by room and floor, and follow up where results are near or above the action level.
2. Commission diagnostics. Request pressure field mapping and an HVAC evaluation before accepting a final design.
3. Review the design. Check the number and location of suction points, fan placement outside occupied space, exhaust discharge location, and any HVAC changes.
4. Coordinate logistics. Schedule noisy coring and pipe installation around occupancy, and confirm fire-rated penetrations and permits.
5. Verify performance. Require post-mitigation testing in every affected area and a written operating and maintenance plan.
6. Communicate results. Share findings with tenants, staff or parents as appropriate, and keep records for future inspections and sales.

Colorado Considerations and Cost Scaling

Colorado

Colorado is widely regarded as a high-radon state, and many Front Range buildings test above the 4 pCi/L action level. Granitic geology, uranium-bearing formations and widespread basements and slab-on-grade construction all contribute. Local building departments and the state radon program can advise on current requirements for testing and new construction, which can differ by jurisdiction and building type. Expansive clay soils in parts of the Front Range add another factor: slab movement can open cracks and joints over time, so sealing and periodic retesting carry extra weight.

How cost scales

Commercial mitigation pricing does not scale neatly with square footage. It scales with the number of zones, suction points and fans; the length and routing of vent pipe through occupied space or up the building exterior; the complexity of sealing elevator pits, trenches and joints; any HVAC adjustments or engineering; after-hours labor; and the diagnostics and post-mitigation testing program. A small single-story office with good sub-slab gravel may cost only modestly more than a large house, while a multi-zone school or a building with dense fill and complex mechanicals can cost many times more. Ongoing costs include electricity for fans, periodic fan replacement, testing and, where used, increased conditioning of outdoor air. Our guides to radon mitigation systems cost and the commercial radon mitigation system walk through the components behind a quote. For broader mitigation methods, see the radon mitigation hub.

When comparing proposals, ask each contractor to describe diagnostics performed, the number and location of suction points, fan models and expected vacuum, how HVAC interactions were evaluated, and the post-mitigation testing plan. Proposals that skip diagnostics on a large building deserve extra questions. The CDC advises relying on a qualified professional because lowering high radon levels requires technical knowledge and special skills.

References

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

Managing a commercial, school or multifamily property along the Front Range with elevated radon results? Share the building details and recent test data and we can help outline a testing and mitigation 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.