ANSI/AARST Radon Standards Explained

1. Who ANSI and AARST are

Before the standards make sense, it helps to know who writes them. ANSI is the American National Standards Institute. It does not write radon standards itself. Instead, it accredits the organizations that do and oversees a consensus process meant to keep any single interest from dominating. AARST is the American Association of Radon Scientists and Technologists, the professional body that develops radon-specific standards through that ANSI-accredited process.

When you see a standard labeled ANSI/AARST, the two names together signal what it is: a radon standard written by AARST and developed under ANSI consensus procedures. That pairing is what gives the document its credibility with lenders, programs, and regulators, because it was produced through an open, reviewed process rather than by any one company.

2. Why consensus standards exist

Radon is invisible and the readings depend heavily on how a building is tested. Two people could measure the same building and get very different numbers if one closes the building properly, places devices in the right rooms, and runs the test for the right duration, and the other does not. A consensus standard removes that guesswork. It spells out device placement, building conditions, test duration, and documentation so that a result is repeatable and means the same thing no matter who performed it.

That repeatability is the whole point for an owner. A number that follows a published protocol is something a lender, a buyer, or a court can rely on. A number from an informal test is just a number. The standards turn radon testing into evidence.

3. The measurement standard: MA-MFLB-2023

For measuring radon in existing multifamily and large buildings, the current consensus standard is ANSI/AARST MA-MFLB-2023. The unusual name describes what it consolidated. The radon field previously used two separate measurement standards: one known as MAMF for multifamily buildings, and one known as MALB for large buildings. MA-MFLB-2023 brought both under a single current document, so the guidance for an apartment community and the guidance for a large commercial building now live in one place.

What the standard governs is the measurement itself: how devices are selected and placed, how the building should be conditioned during the test, how long the test runs, and how the results are documented. You do not need to know the document line by line. The practical version is that a multifamily or large-building radon report should be performed to MA-MFLB-2023, because that is the current measurement standard the rest of the industry recognizes.

4. The new-construction standard: CC-1000

Measurement is only half of the picture. The other half is preventing high radon in the first place, which matters when a building is still on the drawing board. For radon control in new multifamily and commercial construction, the consensus standard is ANSI/AARST CC-1000. Rather than telling you how to measure an existing building, it describes how to design soil-gas-control features into a building as it goes up.

The core idea is that it is far cheaper and more effective to build in radon control during construction than to retrofit it later. CC-1000 addresses the soil-gas-control features that make that possible, so a new building can be designed to keep radon low from day one. For a developer planning a new apartment community or commercial property, CC-1000 is the standard the design team should be working from.

5. Why this matters to an owner

It is fair to ask why a property owner should care about a pair of technical standard numbers. The answer is that the standards are what make a radon report worth anything in a transaction. A report tied to the current ANSI/AARST protocol is defensible. It was produced a recognized way, it can be repeated, and it stands up when a lender or a buyer reviews the file. A report from a generic test kit, or from a method nobody can point to, does not.

For most owners, the standards quietly govern the testing required during a purchase, a refinance, or a financed renovation. You may never read MA-MFLB-2023 or CC-1000, but if your report follows them, you avoid the situation where a deal stalls because the radon documentation does not hold up. The 4.0 pCi/L action level used across US radon programs sits on top of this: a unit at or above that level is mitigated and retested, and the standard is what makes those readings trustworthy.

6. What a lender expects to see

Lenders financing multifamily and commercial property generally do not want to debate radon methodology. They want a report they can file and defend. In practice that means a report that references the current ANSI/AARST measurement protocol, documents how the testing was done, states the levels found, and, where any reading is at or above the action level, describes mitigation and confirms post-mitigation results.

The federal multifamily programs and the government-sponsored enterprises that touch so much of the apartment market lean on these consensus standards rather than writing their own test methods. We cover how those program requirements have shifted in our guides on HUD radon requirements for multifamily and the 2025 Fannie Mae and Freddie Mac radon changes. The program rules change, but the underlying expectation that testing follows a current ANSI/AARST protocol is the constant.

7. The right question when you hire

Owners often ask whether a radon company holds a particular credential. That is a fine question, but it is not the most useful one. The most useful question is whether the testing will be performed to the current ANSI/AARST protocol and how the results will be documented. A provider that can answer that clearly, and point to MA-MFLB-2023 for measurement or CC-1000 for new construction, is giving you a report you can use.

EraseRadon is a team of experienced radon professionals who test to the current ANSI/AARST protocols. The standards in this article are third-party industry standards, and the value to you is a report built around them. When you talk to any provider, including us, hold them to the same questions above.

8. ANSI/AARST testing in metro Atlanta

Georgia does not have a state radon testing law, so for a commercial or multifamily building here the standard that applies usually comes from the program or lender financing the property, not from the state. That makes the ANSI/AARST protocols even more central, because they are the benchmark those programs reference when the state is silent.

It also matters because much of metro Atlanta sits in higher-radon areas. The region's granite and uranium-bearing bedrock pushes readings up, so elevated results are common enough to plan for. Testing a building here to the current protocol is not a formality. It is how you find out what a building actually reads, and it is what keeps a high result from turning into a financing problem. See our multifamily radon overview and our commercial radon testing guide for the practical side of how testing is run.

9. Frequently asked questions