Radon rules for apartment buildings revisited one year later

Less than a year ago, the Federal Housing Finance Authority (FHFA) implemented new standards for radon testing for Fannie Mae and Freddie Mac multifamily loans. Sampling requirements have increased from 10% of ground-floor units to 25% of ground-floor units. Naturally, sampling more units leads to the discovery of more units with elevated radon levels, which translates into a greater need for radon mitigation. Buyers of multifamily properties, as well as their lenders, should know what to expect when faced with a radon mitigation project.

Popular methods of reducing radon

The goal of radon mitigation is to reduce radon levels below the EPA action level of 4.0 pCi/L. There are two common approaches. A sub-slab depressurization system (SSDS) is the most common method. It works by creating a negative pressure zone under the building slab, preventing radon from entering the indoor environment. This system uses a fan to extract radon gas from under the slab and vent it to the outside, where it dissipates safely. The second method uses positive pressure systems — also known as fresh air dilution/intake systems, energy recovery ventilators (ERVs), or heat recovery ventilators (HRVs) — to create a higher pressure inside the building compared to the soil outside. By introducing filtered outside air into the building, these systems prevent radon from entering. Positive pressure systems are often used in Florida and other regions where SSDS may not be feasible.

Factors Affecting Radon Mitigation Costs

Several factors influence the cost and design of radon removal systems:

• Building purpose: multi-family buildingsrequire a different approach than single-family buildings or large commercial buildings.
• Foundation Type: The type of foundation (slab, crawl space, basement, etc.) will impact the design of the system.
• Soil composition: Soil type (clay, sand, silt, etc.) affects the effectiveness of various mitigation techniques.
• Additional industrial hygiene requirements: Tasks such as asbestos and lead removal may be necessary and may impact overall costs.
• Additional services/hidden fees – electrician, roofer, permits, aesthetic options, hiding pipe runs, etc.

Although there is some flexibility in the design of radon mitigation systems, including choices such as fan shrouds, color of vertical risers, and occasionally suction point location, basic design aspects—such as number of suction points, fan size, and suction point location—are usually determined by the radon reducer’s evaluation of the above factors. In complex cases, a prediagnostic study may be required.