Why HUD Cares About Radon
You already know that ground-floor units pose unique environmental liabilities due to direct soil contact.
Understanding the hud radon requirements multifamily developers face is a mandatory step in the environmental review process. Our commercial radon systems team handles the specific testing, mitigation, and paperwork these large-scale projects demand.
Recent 2026 data puts this liability into sharp focus for local developers. Iowa holds the unique distinction of being the only US state where all 99 counties are designated as EPA Radon Zone 1. This classification means the predicted average indoor screening level exceeds the EPA action level of 4.0 pCi/L statewide.
Not legal or lending advice
Program requirements change and vary by loan type. This guide gives a high-level overview. Confirm current requirements with your HUD-approved lender at the start of your project.
Which HUD-Financed Projects Trigger Radon Testing
Section 9.6.3 of the HUD Multifamily Accelerated Processing (MAP) Guide mandates hud radon testing for almost all FHA-insured loans. This requirement ensures safe indoor air quality before any federal funds are committed. The rules apply broadly across several major transaction types.
The MAP Guide triggers environmental testing requirements for the following project categories:
- Section 221(d)(4) new construction
- Substantial rehabilitation projects
- Section 223(f) refinance and acquisition of existing properties
- Low-Income Housing Tax Credit (LIHTC) developments
Other financing sources enforce similar strict policies. Fannie Mae updated its Form 4251 and Form 4099 in 2025 to tighten environmental due diligence across their portfolios. Freddie Mac aligned its policies around the same time, increasing testing density from 10% to 25% for certain conventional loans.
Our advisory team strongly recommends planning for these assessments early in the underwriting phase. The costs of proactive testing pale in comparison to loan delays caused by missing environmental reports.
How Testing Works: ANSI/AARST Multifamily Standards
Testing procedures must strictly follow the ansi aarst multifamily radon measurement protocol known as MAMF-2017. HUD formally adopted this standard to guarantee consistent, scientifically valid measurement across all commercial properties. The guidelines dictate exact monitor placement and strict environmental controls.
These comprehensive standards cover several essential operational phases:
- Identifying which specific units and rooms require assessment
- Calculating the exact number of test devices needed
- Enforcing the minimum 48-hour test duration
- Managing quality control via duplicate tests and blanks
- Formatting the final laboratory data for agency review
We follow these 2021-revised guidelines to the letter during every deployment. The MAMF standard requires careful documentation of building conditions throughout the entire measurement period. Mitigation system design falls under a separate but related code known as ANSI/AARST RMS-MF.
Testing Sample Sizes
The MAMF protocol prohibits single-unit basement testing and requires a comprehensive sampling approach. Accurate risk assessment demands data from multiple locations across the building footprint. A single test simply cannot represent the varying soil conditions under a large foundation.
The latest revisions to the standard established specific minimum sampling percentages. Testers must place devices in 100% of all ground-contact units. A minimum of 10% of upper-floor units must also be tested to verify upward gas migration.
| Area | Typical approach |
|---|---|
| Ground-contact units | All are tested |
| Upper-floor units | A portion is tested, spread across floors |
| Occupied common areas on ground contact | Tested, such as leasing offices or community rooms |
| Quality control | Duplicate tests and blanks per protocol |
| Unoccupied or non-livable areas | Usually not tested |
Our project managers prepare a detailed, unit-by-unit testing map before placing any devices. This blueprint ensures compliance with the specific protocol referenced by your lender.
Scheduling around tenants
Proper scheduling requires coordinating a minimum 12-hour closed-building condition before the 48-hour test even begins. The EPA mandates keeping all windows and outside doors shut during this entire period. Accurate readings depend entirely on maintaining this stable indoor environment.
We manage all tenant notifications to ensure full compliance without burdening your staff. Clear communication helps residents understand the simple instructions regarding closed windows and device access. The process moves smoothly when property managers and testing crews work from a unified timeline.
When Mitigation Is Required
Active mitigation becomes mandatory whenever test results meet or exceed the EPA action level of 4.0 pCi/L. Lenders typically require the installation of a remediation system before the loan can close. The goal is to safely vent the radioactive gas above the roofline.
Larger buildings usually demand complex, engineered solutions. The typical multifamily radon mitigation requirements include:
- Multiple suction points drilled under large or separated concrete slabs
- Commercial-grade fans capable of moving significant air volumes
- Balancing dampers to equalize vacuum pressure across different foundation zones
- Professional sealing of major cracks and utility penetrations
Our installation crews design these systems to operate quietly and efficiently. Post-mitigation clearance testing must occur no sooner than 24 hours after system activation. The affected units must maintain the same strict 12-hour closed-building preparation prior to this final clearance test.
Documentation for Financing
Lenders require a comprehensive environmental review package to satisfy HUD reporting standards. Reviewers carefully examine the data to verify compliance with the accepted ANSI/AARST protocols. Incomplete paperwork will immediately halt the underwriting process.
A complete reporting package must include several specific elements:
- Official laboratory reports showing unit numbers, dates, and pCi/L results
- The detailed testing floor plan and methodology used
- Certification numbers for the credentialed measurement professionals
- Engineered system designs if active mitigation was necessary
- A formal Operation and Maintenance (O&M) plan for installed systems
Our administrative team organizes all these documents into a single, cohesive file. This level of preparation makes it easy for your lender to upload the data into the HUD Environmental Review Online System (HEROS).
Planning Tips for Owners and Developers
Proactive planning prevents loan delays by securing testing resources well in advance of closing dates. Property owners should assume environmental compliance will take significant time. Rushing the process often leads to costly scheduling conflicts.
Here are the most critical planning steps for a smooth transaction:
- Ask your lender early which radon requirements apply and what documentation format they want.
- Build testing into your schedule. Environmental reviews often take 3 to 4 weeks for full deployment, laboratory analysis, and report generation.
- For new construction, plan radon-resistant features during design. Installing passive systems early costs much less than retrofitting active fans later. See radon-resistant new construction in Iowa.
- For existing buildings, test well before closing so there is ample time to mitigate if elevated levels are found.
- Keep records after closing. You will need these baseline readings for future refinancing and mandated retesting cycles.
We highly recommend booking your environmental assessments the moment you initiate the loan application. This strategy creates a comfortable buffer for any required mitigation work.
Iowa Multifamily Experience
Local expertise ensures your project meets both federal guidelines and state-specific licensing laws. Iowa Code Chapter 136B strictly regulates who can perform commercial testing services within the state. Hiring an uncredentialed vendor will invalidate your entire environmental report.
Our testing is conducted exclusively by specialists credentialed through the Iowa Department of Health and Human Services (HHS). The state requires these specific credentials for any commercial measurement work. We manage massive unit counts across Des Moines, Ames, Cedar Rapids, Iowa City, Waterloo, and the Quad Cities.
Large buildings require contractors who completely understand commercial-scale ventilation dynamics. For single-unit homes and smaller rentals, standard radon testing works well. Meeting the strict hud radon requirements multifamily properties face requires absolute precision. Send us your unit count, building layout, and lender requirements, and our team will scope the testing plan to deliver a firm project price.