Apartment Buildings and Radon: Landlord Liability and Best Practices

The radon conversation in Michigan is overwhelmingly framed around single-family homeowners — and for good reason, since homeowners make the testing and mitigation decisions for their own properties independently. But a substantial portion of Michigan's housing stock is occupied by renters, and the radon dynamics in rental housing — particularly in apartment buildings and multi-unit properties — create a distinct set of responsibilities, risks, and practical considerations that fall primarily on landlords and property managers rather than on the tenants who are actually being exposed.

This post addresses the landlord and property manager perspective on radon in multi-unit residential buildings. Commercial building radon was covered in our post on radon in commercial buildings. The tenant rights dimension and the specific practical testing protocols for rental properties receive dedicated treatment here because the multi-unit context differs meaningfully from both single-family residential and commercial settings.

Why Multi-Unit Buildings Are Not Lower Risk

A common misconception among landlords encountering the radon question for the first time is that apartment buildings — by virtue of being larger, taller, or differently constructed than single-family homes — are somehow less susceptible to radon than residential houses. This assumption does not hold up under examination.

Radon entry in a multi-unit building follows the same physical principles as in a single-family home. The building sits on a foundation above radon-producing geology.

Pressure differences between the sub-slab environment and the building interior drive soil gas — and radon — upward through foundation cracks, utility penetrations, slab joints, and any available pathway. Ground-floor and basement units in multi-unit buildings are exposed to the same radon entry dynamics as the ground floor and basement of a single-family home sitting on the same geology.

What differs in a multi-unit building is not the fundamental radon exposure risk for ground-level occupants but the distribution of that risk across a building population and the concentration of decision-making authority in the landlord rather than the individual resident. A single-family homeowner who discovers elevated radon can act immediately — testing, mitigating, and verifying on their own timeline. A tenant in a ground-floor apartment with elevated radon depends entirely on their landlord's willingness to test and act.

Michigan's Regulatory Landscape for Rental Properties

Michigan does not currently require landlords to test rental properties for radon or to disclose radon test results to tenants. There is no provision in Michigan's landlord-tenant law that specifically addresses radon, no building code requirement for radon testing in existing rental buildings, and no regulatory standard for acceptable radon levels in rental housing.

This places Michigan in the majority of states on this issue — most states have not yet extended radon requirements into the rental housing sector. Illinois is a notable exception, having updated its Tenant Radon Protection Act in 2024 to require landlords to provide tenants with radon information and documentation of testing results. Minnesota's radon licensing framework and disclosure requirements apply to real estate transactions that include rental properties. Michigan has neither of these frameworks in place.

The absence of legal requirements does not mean the absence of responsibility. Michigan landlords operate under a general habitability obligation — the requirement to maintain rental units in a condition that is fit for human occupation and free from conditions that materially endanger the health and safety of tenants. Whether an elevated radon level in a rental unit rises to a habitability violation has not been definitively established through Michigan case law, but the trajectory of radon recognition as a significant health hazard — and the increasing body of case law in other states — suggests that landlords who knowingly allow tenants to occupy units with documented elevated radon face meaningful legal exposure.

The Liability Trajectory

Radon liability for landlords is an area of law that is actively developing nationally, and Michigan landlords who assume that the current absence of explicit requirements means indefinite protection from liability are making a risk assessment that deserves scrutiny.

The pattern in states that have established radon liability precedents generally follows a logical sequence. A tenant develops lung cancer. Medical evidence establishes that radon exposure is a contributing cause. The tenant or their estate investigates the radon history of the unit and discovers either that testing was never conducted or that elevated levels were documented and not addressed. Litigation follows on theories of negligence, breach of warranty of habitability, or intentional concealment of a known hazard.

The landlord's defense in this sequence is weakest when they had knowledge of elevated radon — through their own testing or through a tenant complaint — and took no action. It is somewhat stronger, but not invulnerable, when they had no knowledge because they never tested. The argument that a landlord should have known about a recognized health hazard affecting their property — particularly in a Zone 1 county where the geological risk is documented and publicly available — becomes more available to plaintiffs as radon awareness increases among the general public and the professional property management community.

Proactive voluntary testing is the most effective liability management strategy available to Michigan landlords in this environment. A landlord who has tested all ground-floor and basement units, addressed elevated findings through mitigation, and documented the results has a defensible record of responsible property management. A landlord who has never considered radon has no such record.

Testing Protocols for Multi-Unit Buildings

Professional radon testing in multi-unit buildings requires a different approach than single-unit residential testing, reflecting the larger footprint, multiple occupied spaces, and varying radon exposure profiles across the building.

The fundamental protocol for multi-unit radon testing follows EPA and AARST guidance that focuses testing on the ground floor and basement units — the spaces with the most direct foundation contact and the highest radon entry potential. Upper-floor units in mid-rise and high-rise buildings are generally not the priority for initial testing, as radon levels in these spaces are typically much lower than in ground-level units due to the distance from the entry source and the dilution that occurs as radon migrates upward through the building.

For low-rise apartment buildings — two and three-story buildings that make up the majority of Michigan's multi-unit rental stock — testing should include all ground-floor units and any basement-level units. The number of test devices required depends on the number of units and the building's footprint. Unlike a single-family home where one device in the basement provides a meaningful characterization of the building's radon profile, a multi-unit building with multiple ground-floor units may show significant variation in radon levels from unit to unit depending on the specific sub-slab conditions beneath each unit and the individual unit's construction details.

This variation — the possibility that one ground-floor unit has a significantly different radon level than its neighbor in the same building — is one of the characteristics of multi-unit testing that makes comprehensive unit-by-unit testing more informative than a single representative sample. Two adjacent ground-floor units may have different levels because of differences in the aggregate beneath their specific floor area, differences in how their utility penetrations are sealed, or differences in their HVAC configuration and how it affects local pressure dynamics.

Practical Landlord Considerations

Beyond the liability and protocol dimensions, several practical considerations shape how Michigan landlords should approach radon in their rental portfolios.

Tenant cooperation during testing is a practical requirement that differs from the single-family context. Closed-house conditions during a short-term test require tenant awareness and cooperation — windows kept closed, normal activity otherwise maintained. Coordinating this with tenants requires communication about the purpose and process of testing in a way that is informative without being alarming. A straightforward communication — explaining that radon testing is a routine health and safety measure, describing what the test involves and what tenants should do during the test period — is both more effective and more legally appropriate than conducting testing without tenant awareness.

Mitigation in multi-unit buildings follows the same sub-slab depressurization principles that apply to single-family homes but must be designed to address the larger and potentially more complex footprint of a multi-unit building. A building with ten ground-floor units occupying a substantial total floor area may require multiple suction points, higher-capacity fans, and more extensive pipe routing than a single-family installation. The diagnostic assessment process — communication testing, suction point evaluation — is correspondingly more involved.

Tenant notification of elevated results is both a practical and ethical obligation that Michigan landlords should treat as mandatory regardless of whether state law explicitly requires it. A landlord who discovers elevated radon levels in occupied units and does not inform tenants is making a decision to conceal a known health risk from the people experiencing it — a position that is ethically indefensible and legally risky.

Building Radon Testing Into Property Management Practice

The most effective approach to radon management for Michigan landlords is not reactive but systematic — incorporating radon into the standard property management framework rather than addressing it only when a specific concern arises.

For a landlord acquiring a new property, testing ground-floor and basement units as part of the acquisition due diligence process — similar to commissioning a general property inspection — establishes baseline knowledge and informs the purchase decision. As we discussed in our post on radon due diligence for property investors, the information gathered during acquisition is actionable in a way that post-acquisition discoveries are not.

For existing portfolio properties that have never been tested, a systematic testing program — working through the ground-floor and basement units of each building over a defined timeline — converts an unknown risk into a known and managed one. The cost of systematic testing across a rental portfolio is modest relative to annual operating expenses and the potential liability it addresses.

Periodic retesting at the standard two-year interval maintains the knowledge base that initial testing establishes, catching any performance changes in mitigation systems and any new radon entry that has developed as buildings age.

A Note on Section 8 and Affordable Housing

Michigan landlords who participate in the Section 8 Housing Choice Voucher program or other federally assisted housing programs should be aware of HUD's 2024 radon policy update requiring radon testing and mitigation plans for federally assisted housing projects. This federal policy change represents the most significant regulatory development in rental housing radon in recent years, and its implementation requirements for Michigan landlords in the federal housing assistance programs are worth understanding and complying with proactively.

Affordable housing providers who serve lower-income tenants — a population that may have less ability to advocate for their own housing conditions and less awareness of radon as a health concern — have a particular responsibility to ensure that the units they provide are tested and, where elevated levels are found, mitigated. The health equity dimension of radon in affordable housing is not abstract — lower-income renters in older buildings in Zone 1 counties are among the populations most likely to experience elevated radon exposure and least likely to have the resources or leverage to address it independently.

At All Michigan Mitigation, we work with landlords and property managers throughout West Michigan on multi-unit radon testing and mitigation, bringing the technical expertise and institutional experience that rental property assessments require. Radon is the only thing we do, and we understand the practical constraints and professional obligations that property management involves.

Visit us at allmichiganmitigation.com to discuss radon testing and mitigation for your rental portfolio or to learn more about what a multi-unit assessment involves.

All Michigan Mitigation is a West Michigan radon testing and mitigation company dedicated exclusively to helping homeowners understand and eliminate radon risk in their homes.