HUD Radon Requirements for Multifamily Properties

1. Which HUD loans require radon testing

HUD insures and finances a large portion of the country's apartment stock through its multifamily mortgage programs. When a property is financed or refinanced through these programs, radon is part of the environmental review, and testing is generally expected. The most common touchpoints are the Multifamily Accelerated Processing (MAP) programs for apartments and the Section 232 program for residential care facilities.

The practical trigger for most owners is a transaction. A purchase, a refinance, or a new HUD-insured loan brings the environmental review into play, and that review is where the radon requirement lives. If you are buying or refinancing an apartment community with HUD financing, plan for radon testing as part of due diligence.

2. How many units you have to test

This is the rule that changed most recently, and it is where outdated guidance still circulates. For years, the common figure was that you tested 25 percent of ground-floor units. HUD found that approach missed too many elevated units and moved to a more extensive sampling standard. Because HUD has updated these requirements and the exact count depends on the building, treat any single fixed percentage as a starting point only, and confirm the controlling requirement for your loan with your lender.

The reason is simple. Radon enters from the soil, so ground-contact units carry the highest risk, but upper floors are not automatically safe, especially in buildings with elevator shafts, stairwells, and other vertical pathways that let soil gas move upward. Testing only a fraction of ground-floor units can leave elevated units undiscovered, which is exactly the gap HUD closed.

3. The 4.0 pCi/L action level

HUD uses an action level of 4.0 pCi/L, the same threshold used across most US radon programs. Any unit that tests at or above 4.0 pCi/L has to be mitigated, and the work is not finished until post-mitigation testing confirms the unit reads below 4.0 pCi/L. Freddie Mac's published multifamily standard uses the same post-mitigation confirmation requirement, which you can see in its radon testing and mitigation standards.

It is worth being precise about what the action level means. It is the level at which action is required, not a line between safe and dangerous. Radon risk is continuous, so a building reading just under 4.0 pCi/L still carries risk, and many owners choose to mitigate below the action level when the cost is modest and the building is occupied long term.

4. The testing protocols HUD points to

HUD does not invent its own test method. It points to the consensus standards published by ANSI and the American Association of Radon Scientists and Technologists (AARST). For measuring radon in existing multifamily and large buildings, the current standard is ANSI/AARST MA-MFLB-2023, which consolidated two older standards (MAMF for multifamily and MALB for large buildings) into one. For radon-resistant features in new construction of multifamily and commercial buildings, the standard is ANSI/AARST CC-1000.

For owners, the takeaway is that these are third-party standards your testing should follow, and they are what a lender will expect to see referenced in a defensible report. When you choose a provider, the right question is whether the testing is performed to the current ANSI/AARST protocol, not whether a generic home test kit was used. You can review the published standards through the AARST standards library.

5. Section 232: senior living and residential care facilities

HUD's Section 232 program insures loans for residential care facilities, which includes assisted living, skilled nursing, and memory care. Because these buildings house a vulnerable population, the radon requirement is explicit: a radon report is required for a Section 232 mortgage insurance application unless a specific exception in the program handbook applies.

HUD also specifies who prepares that report. It must be signed by a radon measurement professional credentialed under a recognized program such as AARST or NRSB, working to ANSI/AARST protocols, and state certification applies where a state requires it. For senior living owners, this is the strictest and clearest radon requirement in the HUD system, and it is worth scheduling early in the loan timeline so it does not delay closing.

6. HUD environmental reviews and Notice CPD-23-103

In January 2024, HUD issued Notice CPD-23-103, its departmental policy for addressing radon in the environmental review process. The notice took effect for most recipients in April 2024. Its core rule is straightforward: where radon is found at or above 4.0 pCi/L in any building or unit, mitigation is required, and the environmental record must include a mitigation plan that identifies the level, describes the reduction system, and provides for post-installation testing.

You can read the policy directly through the HUD Exchange radon policy page. For owners of HUD-assisted properties, the practical message is that radon is now a standing part of the environmental review, not an afterthought.

7. How HUD differs from Fannie Mae and Freddie Mac

It is easy to lump all federal multifamily radon rules together, but HUD is separate from the requirements that apply to Fannie Mae and Freddie Mac loans. In March 2025, the Federal Housing Finance Agency rescinded a 2022 directive that had standardized radon testing across Fannie Mae and Freddie Mac. After that change, each of those enterprises sets its own multifamily radon requirements, and an environmental professional's judgment, along with state and local law, plays a larger role.

HUD's own requirements, the subject of this article, were not part of that rescission and remain in force. So the rules that apply to your property depend on how it is financed. For a detailed breakdown of the Fannie Mae and Freddie Mac changes, see our companion guide on the 2025 Fannie Mae and Freddie Mac radon changes, and our overview of multifamily radon testing.

8. What HUD radon work costs

Costs fall into two buckets: testing and, if needed, mitigation. Testing a multifamily property is priced per unit, and larger buildings benefit from economies of scale because crews place and retrieve many devices in one mobilization.

Mitigation is the larger number, and it only applies to units that test high. A 2025 cost analysis published by AARST modeled mitigation at roughly $2,400 to $4,000 per affected unit, which on a 155-unit example property worked out to about $387 to $645 per unit spread across the whole property. You can review that analysis in the AARST multifamily radon cost document. Because mitigation depends on how many units read high and on the building's construction, a firm number comes after testing and a site visit.

9. Radon risk in metro Atlanta

Georgia does not have a state radon testing law, which leads some owners to assume radon is not a local concern. The data says otherwise. On the EPA Map of Radon Zones, four metro Atlanta counties, Fulton, Cobb, DeKalb, and Gwinnett, are Zone 1, the highest category, meaning a predicted average at or above 4.0 pCi/L. Several surrounding north Georgia counties also carry elevated designations driven by the region's granite and uranium-bearing bedrock.

For a HUD-financed property in metro Atlanta, the combination of federal testing requirements and genuinely elevated regional radon means high results are common enough to plan for. Building the testing timeline into your loan process, rather than reacting to it, keeps a high reading from turning into a closing delay.

10. Frequently asked questions