Radon Testing in Multifamily Housing: A Guide
Radon testing in multifamily housing is more involved than testing a single-family home, because an apartment building, condominium, or townhome complex may have dozens of ground-contact units, multiple foundation types, and shared ventilation that all affect how radon behaves. Radon is a colorless, odorless radioactive gas and the leading cause of lung cancer among non-smokers, and along Colorado’s Front Range, where radon potential is elevated, multifamily owners and residents have good reason to take it seriously. This guide summarizes EPA and Colorado Department of Public Health and Environment guidance current as of 2026; consult a certified professional for testing decisions and your physician for any health concerns. It explains how multifamily testing works, who is responsible, and what the results mean.
Part of our Radon Levels guide — start there for the full picture →
How does radon testing in multifamily housing work?
Radon enters buildings from the soil beneath them, so the units most at risk are those in contact with the ground: ground-floor apartments, basement units, and townhomes built on slab or basement foundations. In a multifamily building, radon can vary substantially from one unit to another depending on foundation contact, construction details, and air movement, which is why testing follows specific protocols rather than a single whole-building measurement.
Professional multifamily testing typically uses an EPA-referenced protocol for measuring radon in multifamily and similar buildings. Rather than testing every single unit, the protocol provides guidance on how many and which units to test, focusing on ground-contact units and using a representative sampling approach for larger buildings. The goal is a reliable picture of radon across the building, not a single reading that might miss a high unit on the ground floor while a top-floor unit reads low.
Which units should be tested?
The priority is ground-contact units, since they have the most direct pathway for soil gas to enter. In a building with a basement level, basement and first-floor units warrant testing. Units on upper floors that sit above other occupied units are at much lower risk because radon concentration generally decreases with height above the soil.
Sampling in larger buildings
For a building with many ground-contact units, testing protocols allow for a representative sample rather than testing every unit, though the sampling approach is designed to give confidence that elevated levels would be detected. The exact number depends on the building’s size and configuration. Smaller buildings, such as a duplex or fourplex, may simply have all ground-contact units tested. A certified professional determines the appropriate scope for a given building.
Shared and common areas
Common areas in contact with the ground, such as a basement laundry room, storage area, or community space, may also be tested, since residents spend time there and radon can accumulate in below-grade common spaces. The broader principles of where and how radon is measured are covered in our guide to radon measurement.
Who is responsible for radon testing in multifamily housing?
Responsibility depends on ownership structure and, in some cases, on funding or regulatory requirements. In a rental building, the owner or property management company is generally the party able to arrange building-wide testing, since individual tenants control only their own units. In a condominium, the homeowners association often handles common elements and may coordinate testing, while individual owners are responsible for their own units in some arrangements.
Certain federally assisted or financed multifamily housing may be subject to specific radon testing and mitigation requirements as a condition of funding, particularly under HUD-related programs. Owners of such properties should verify their obligations. Regardless of any mandate, testing is a sound risk-management step. A resident concerned about radon in a rental should raise it with the property owner or manager, and an individual condo owner can arrange testing for their own unit. For a unit-level perspective, our guide on radon in apartments addresses what individual tenants and owners can do.
What do multifamily radon results mean?
Results are reported in picocuries per liter, or pCi/L, the same unit used for single-family testing. The EPA action level is 4.0 pCi/L; at or above that level in a tested unit or common area, mitigation is recommended. Because radon varies between units, a result applies to the unit or area tested, and an elevated reading in one ground-floor unit signals that other ground-contact units deserve attention even if a representative sample was used.
As with single-family testing, a short-term result is a screening that may warrant confirmation, and conditions during the test matter. Professional testing in occupied multifamily buildings often uses continuous radon monitors or tamper-resistant devices, especially when the result will inform decisions affecting tenants or a transaction. The Front Range radon testing hub explains why Colorado’s geology makes elevated readings common and worth acting on.
Mitigation in multifamily buildings
When elevated radon is confirmed, mitigation in a multifamily building can be more complex than in a single-family home, but the underlying approach is the same: prevent soil gas from entering and vent it safely outdoors. Active soil depressurization, which uses a fan and piping to draw radon from beneath the foundation and exhaust it above the roofline, is the most common method. In a multifamily building, a system may serve multiple units or sections, and the design must account for the building’s foundation layout and any shared spaces.
Because the engineering can be involved, mitigation in multifamily housing should be designed and installed by certified professionals experienced with larger buildings. After installation, retesting confirms that levels have dropped below the action level. Coordinating mitigation across occupied units requires planning around residents, which is another reason professional management of the project matters.
Why multifamily testing is more complex than a single home
Several factors make a multifamily building harder to assess than a single-family house, and appreciating them explains why the protocols exist. A house has one household, one foundation footprint, and one set of operating conditions. A multifamily building has many units, each operated differently by its occupants, sometimes with different foundation contact and often with shared mechanical systems that move air between spaces. Radon can therefore vary widely from one unit to the next within the same building.
Shared ventilation and pressure dynamics add another layer. Heating, cooling, and exhaust systems, along with stairwells and elevator shafts, can move air in ways that affect how radon distributes and accumulates. A change in one part of the building, such as a new exhaust fan or a sealed basement, can alter radon behavior elsewhere. These interactions are why a single whole-building reading is inadequate and why a structured, professional approach to which units to test, and how, produces a more trustworthy picture than informal spot-checking.
What building owners gain from testing
For an owner or manager, radon testing is not only a health measure but a sound risk-management practice. Documenting that a building has been tested, and mitigating where levels are elevated, demonstrates a good-faith effort to protect residents. It can also smooth transactions, since a prospective buyer of the building will ask about radon, and existing test and mitigation records answer that question cleanly.
Tenant relations benefit as well. Residents increasingly ask about indoor air quality, and an owner who can show that ground-contact units have been tested and addressed builds trust. Along the Front Range, where elevated radon is common, proactive testing positions an owner ahead of resident concerns rather than reacting to them. The modest cost of testing a representative sample of ground-contact units is small compared with the value of documented, demonstrable diligence.
What devices are used for multifamily testing
Professional multifamily testing tends to rely on more capable devices than the simple passive kit a single homeowner might use, because the stakes and the need for reliability are higher. Continuous radon monitors record hourly readings over the test period and can detect interference, such as a window being opened during a closed-house test, which makes the result more defensible. These devices are particularly valuable in occupied buildings where conditions are harder to control.
Tamper-resistant passive devices are also used, especially when many units must be tested at once and continuous monitors are not practical for every location. The choice of device depends on the building, the number of units, whether the result will inform a transaction, and the level of confidence required. A certified measurement professional selects the appropriate equipment and placement for each situation. Our overview of how radon is measured covers the underlying principles that apply whether the device is a simple kit or a continuous monitor.
Coordinating testing across occupied units
Testing an occupied multifamily building introduces logistical challenges that a single-family test does not. Each unit’s residents operate their space differently, opening windows, running fans, and adjusting thermostats, which can affect readings if not managed. Closed-house conditions, where windows and exterior doors stay shut during a short-term test, are harder to maintain across many independent households, so professionals account for this through device choice, test duration, and resident communication.
Access is another consideration. Testing ground-contact units requires entering them, which means coordinating with residents and scheduling around their availability. Clear communication about why the testing is happening, what residents need to do, and how the results will be handled smooths the process and builds trust. For owners and managers, planning the testing campaign carefully, rather than treating it as an afterthought, produces more reliable results and a better experience for residents. The effort is manageable, and the payoff is a documented, trustworthy picture of radon across the building.
Testing during transactions and renovations
Radon testing often arises during the sale of a multifamily property or a condominium unit, and during major renovations that disturb the foundation or change a building’s airflow. For transactions, professional, tamper-resistant testing is the appropriate standard, since the result can affect price and obligations. Buyers of a multifamily property should ask whether the building has been tested and request to see any prior results and mitigation records.
Renovations are worth flagging because changes to foundations, ventilation, or how a building is sealed can alter radon levels, sometimes raising them. After significant renovation in a building with ground-contact units, retesting is prudent. Treating radon as part of the building’s ongoing maintenance, rather than a one-time check, keeps residents protected as the building changes over time.
Condominiums: a special case
Condominiums sit between rental and single-family ownership, which complicates responsibility for radon. In most condominium arrangements, the homeowners association owns and manages the common elements, including the building structure and often the foundation, while individual owners hold their units. Radon enters through the foundation, a common element, but accumulates in individual units, so addressing it can involve both the association and individual owners.
For a condominium owner, this means a confirmed elevated reading in a ground-floor unit may require coordination with the association, since mitigation typically involves the building’s foundation. An owner concerned about radon can test their own unit independently, but resolving an elevated result usually means engaging the association’s governance. Prospective condominium buyers, especially of ground-floor units along the Front Range, should ask whether the building has been tested, whether the association has addressed radon, and how the governing documents allocate responsibility. Understanding this structure before buying prevents surprises about who pays for and arranges mitigation. The unit-level perspective in our guide on radon in apartments and condos complements this building-wide view.
References
- EPA radon measurement protocols and definitions — U.S. Environmental Protection Agency
- Colorado radon testing and mitigation guidance — Colorado Department of Public Health and Environment
- Radon health risks and testing recommendations — American Lung Association
Frequently asked questions
Which units should be tested for radon in a multifamily building?
Ground-contact units, including basement and first-floor apartments and townhomes on slab or basement foundations, are the priority because soil gas enters most directly there. Larger buildings may use a representative sample of ground-contact units, with upper floors at much lower risk.
Who is responsible for radon testing in an apartment building?
In rentals, the owner or property manager generally arranges building-wide testing. In condominiums, the HOA may handle common areas while owners handle their units. Some federally assisted housing has specific radon requirements tied to funding.
What radon level requires action in a multifamily unit?
The EPA action level is 4.0 pCi/L, the same as for single-family homes. At or above that in a tested unit or common area, mitigation is recommended. An elevated ground-floor reading signals that other ground-contact units deserve attention.
Is mitigation different in multifamily housing?
The approach is the same, active soil depressurization that vents radon above the roofline, but the engineering is often more complex because a system may serve multiple units. Certified professionals experienced with larger buildings should design and install it, followed by retesting.
Front Range property owners and residents who want professional radon testing or mitigation guidance for a multifamily building can connect with a vetted local inspector through our contact page.
Test your home for radon
Radon is invisible and odorless, so a test is the only way to know your level. A short-term kit gives a first reading in days; a digital monitor tracks it over time.
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 AirChek Charcoal Radon Test Kit | Lab fee usually included; EPA short-term protocol. | Amazon — $21.95 |
 First Alert RD1 Radon Test Kit | Widely stocked; 48-hour charcoal test. | Amazon — $16.98 |
 Airthings Corentium Home | Digital monitor with a long-term average. | Amazon — $142.99 |