Lender Radon Requirements, Explained

Radon Requirements for Multifamily Lenders, 2026

There is no longer a single universal radon testing threshold for agency multifamily loans: FHFA rescinded its standardizing directive in March 2025, Fannie Mae now leaves scoping to the environmental professional, Freddie Mac requires a minimum of 10% of ground-contact units with at least one test per building where testing is warranted, and HUD and FHA continue under their own program rules. Which one applies to you depends on your loan.

This page exists because we spent most of 2025 answering the same question from owners who had read something written in 2023. Here is where it actually stands.

How It Got Here

1. Before 2023: both Fannie Mae and Freddie Mac had radon policies, and they were not identical.
2. June 30, 2023: the Enterprise Multifamily Radon Policy took effect under FHFA direction, standardizing testing at 25% of ground-contact units with a minimum of one test per building, up from 10%.
3. March 26, 2025: FHFA rescinded the directive behind that policy, citing added time, expense and operational complexity for Enterprise transactions.
4. After the rescission: Fannie Mae removed the fixed schedule from its Multifamily Guide; Freddie Mac updated its standards to a 10% minimum applied where the consultant concludes testing is warranted. HUD was never part of the FHFA action and continued on its own track.

Program by Program

Program	Current posture	Practical effect
Fannie Mae Multifamily	No fixed percentage; environmental professional determines scope based on property type, geology, and state or local requirements	Scope varies by deal. In LA County the low regional rate is a legitimate input, but it is not an automatic waiver
Freddie Mac Multifamily	Minimum 10% of ground-contact units, at least one test per building, where testing is warranted	A defined floor when triggered, roughly 60% less testing than the 2023 standard
HUD / FHA Multifamily	Testing required under ANSI/AARST protocols; ASTM E2121 referenced for existing low-rise residential; 4.0 pCi/L action level; broader sampling since 2025	The most prescriptive of the three. Assume testing
Bank / life company / CMBS	Varies entirely by lender policy and the Phase I consultant's scope	Ask at application. Some never mention radon; some mirror agency practice

What Counts as a Ground-Contact Unit

Any unit with occupied space on or below grade. In practice: slab-on-grade first floors, units above crawl spaces, partially below-grade units on sloped sites, and residential floors directly above enclosed subterranean parking. Second-floor units over an open breezeway generally do not count.

Getting this classification right before you price anything matters, because on a typical LA garden-style property it is the difference between testing fourteen units and testing forty.

What the Report Has To Contain

• Protocol named (ANSI/AARST measurement protocol, or ASTM E2121 where HUD applies)
• Ground-contact unit determination and the reasoning behind it
• Device serial numbers and calibration dates
• Deployment and retrieval timestamps
• Documented building conditions during the measurement period
• Results by unit or room, with locations identified findably
• Mitigation description and post-mitigation verification results where applicable
• Signature of a CDPH-listed professional

A report missing calibration dates or building conditions is the most common reason a consultant sends one back, and each round trip costs you a week you probably do not have.

The Timeline Problem

The recurring failure mode is not the testing. It is when the testing gets scoped. Radon shows up on day 18 of a 30-day due diligence window, needs a 48-hour tenant notice, a deployment pass, 48 to 96 hours of measurement, a retrieval pass, a report, and then potentially mitigation and a verification test. That does not fit, and the extension costs more than everything else combined.

Ask your lender and your Phase I consultant about radon at application. In a market like Los Angeles the answer is frequently "limited scope" or "not warranted," and finding that out in week one is free.

Verify This Yourself

The Federal Housing Finance Agency publishes its directives and rescissions, and HUD publishes the mortgagee letters and MAP Guide provisions governing FHA multifamily radon requirements. Your lender's own guide is the controlling document for your specific loan, and it changes. We keep current on these because we get asked weekly, but confirm with your lender rather than with a contractor's web page, including this one.

Lender Requirement Questions

Is radon testing required for multifamily loans in 2026?

It depends on the program and the deal. FHFA rescinded its 2023 radon directive on March 26, 2025. Fannie Mae then removed the fixed requirement to test 25% of ground-contact units, leaving scope to the environmental professional based on property type, geology and local requirements. Freddie Mac retained a minimum but reduced it to 10% of ground-contact units with at least one test per building, applied where its consultant concludes testing is warranted. HUD and FHA multifamily programs continue to require radon testing under their own rules. So: ask your lender and your consultant at application, not at closing.

What changed in March 2025?

FHFA rescinded the directive that had standardized the enhanced radon policy across Fannie Mae and Freddie Mac, on the stated grounds that the requirements added time, expense and operational complexity inconsistent with its priorities as conservator. Importantly, FHFA did not order the Enterprises to abandon radon policies, and both had policies before 2023. They simply now differ from each other.

What is the action level and what happens above it?

4.0 pCi/L. Any tested space at or above it must be mitigated and retested until it reads below.

Who is qualified to do the testing for a lender file?

In California, a professional listed by the California Department of Public Health, which requires NRPP or NRSB certification. The reviewer will check that the individual signing the report holds the credential, not merely that the company appears somewhere on a list. Mitigation additionally requires a California contractor's license in classification B, C-20, C-36 or D-64.

Does HUD have different rules than Fannie and Freddie?

Yes, and HUD's have been more stable. FHA multifamily programs require radon testing under ANSI/AARST protocols with mitigation and retesting above 4.0 pCi/L, referencing ASTM E2121 for existing low-rise residential structures, and HUD updated its sampling approach in 2025 to cover more units than the older percentage-based approach. Check the current MAP Guide requirements with your lender, because this is the program where the requirements are most prescriptive.

Our property is in Los Angeles, a low-radon county. Does that reduce the scope?

It can, now that scoping rests more heavily on professional judgment. Local geology is an explicit input into the environmental professional's determination, and Los Angeles County's roughly 1% elevated rate is a legitimate factor. It is not a blanket exemption, and properties in the hillside zip codes along the southern San Fernando Valley should be scoped as if they were anywhere else.