HUD Radon Requirements for Multifamily Housing

For most HUD-financed multifamily housing, radon has to be handled two ways, and which one applies depends on whether the building already exists or is being built. Existing buildings HUD finances are tested to the ANSI/AARST protocols, with a 4.0 pCi/L action level that triggers mitigation. New multifamily construction is designed for radon control to ANSI/AARST CC-1000-2018 from the start. Both obligations trace to the same source: HUD recognizes the ANSI/AARST consensus standards, and so does the EPA, which treats them as the radon standards of practice.

This page covers what HUD actually requires, which programs trigger it, what the 4.0 pCi/L action level means in practice, and what a radon design package for new multifamily construction has to contain to clear review.

HUD's radon policy splits along the age of the building.

• For existing multifamily buildings HUD is financing or refinancing, the requirement is a radon test conducted to ANSI/AARST protocols. If results come back at or above the action level, affected units are mitigated and retested until they read below it.
• For new multifamily construction, the requirement is a radon control system designed and built to ANSI/AARST CC-1000-2018, the consensus standard for soil gas control in new large buildings. The one exception is buildings made up of one- and two-family dwellings, which fall under the residential standard instead.

The distinction matters because the two paths produce different deliverables. Testing produces a measurement and, where levels are high, a mitigation plan. New construction produces an engineered design that has to be in the permit set before the slab is poured.

Radon surfaces across HUD's environmental review because site contamination has to be considered under HUD's environmental regulations at 24 CFR parts 50 and 58. On top of that baseline, several program tracks carry their own, more specific radon requirements:

• Multifamily mortgage insurance processed under the Multifamily Accelerated Processing (MAP) Guide.
• Healthcare facilities financed under HUD's healthcare mortgage insurance program.
• Properties moving through the Rental Assistance Demonstration (RAD) program.

If your project runs through any of these, expect radon to be a named item in the environmental review, and, for new construction, a design keyed to CC-1000-2018 in the documents your lender and plan reviewer approve.

The action level for radon in a HUD-financed building is 4.0 pCi/L, the same threshold the EPA uses. It is less a pass or fail grade on the building than a trigger for a defined sequence:

1. Test the building to ANSI/AARST protocols.
2. For any unit at or above 4.0 pCi/L, install a radon reduction system.
3. Retest after mitigation to confirm the unit now reads below 4.0 pCi/L.

For existing buildings, HUD expects the environmental record to carry a mitigation plan that names the level found, describes the reduction system, sets a timeframe for the work, and requires post-installation testing. For new construction, the cleaner move is to design the control system in from the start, so the finished building is unlikely to test high in the first place.

CC-1000-2018 is prescriptive. It sets minimum requirements for buildings intended for human occupancy other than one- and two-family dwellings, which puts apartments, condominiums, congregate housing, schools, and commercial spaces inside its scope. A compliant design specifies:

• A gas-permeable collection layer and suction points beneath the slab, laid out across the full building footprint.
• A continuous soil gas barrier, sealed at every penetration, footing, and construction joint.
• Vent stacks routed from the suction points to a discharge above the roofline, clear of windows and air intakes.
• Passive operation by default, engineered so a fan can be added later without cutting back into a finished slab.

Every CC-1000 design starts passive and is built so it can convert to active sub-slab depressurization if post-construction testing shows the passive draw is not enough. Because the fan location, wiring, and labeling are already drawn on the sheets, that conversion is a field change rather than a redesign. Our multifamily radon design page walks through what the package covers for an apartment or mixed-use building.

A HUD-financed new-construction project does not clear review on a design that only gestures at radon. The reviewer and the lender both expect a package that:

• Is keyed explicitly to ANSI/AARST CC-1000-2018 and references the standard where it applies.
• Is reviewed and signed by a certified radon professional, the credential the compliance chain looks for.
• Travels as standalone sheets inside the permit set, so the contractor installs from it and the examiner checks it without radon being buried in an installer's bid.

A design that meets those three tests answers the radon question before the reviewer has to ask it, which is what keeps HUD financing on schedule.

If you are scoping a HUD-financed apartment, condominium, or mixed-use building, request a quote with your architectural plans and we return a fixed price for a stamped, CC-1000-2018 design package before any work begins.