Just over a year ago, the Federal Housing Finance Authority (FHFA) implemented new standards for radon screening for Fannie Mae and Freddie Mac multifamily loans. Sampling requirements increased from 10% of ground floor units to 25% of ground floor units. Naturally, sampling more units leads to discovering more units with elevated radon levels, which translates to more 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. 

Common Radon Mitigation Methods

The intent of radon mitigation is to reduce radon levels below the EPA action level of 4.0 pCi/L. There are two common approaches. The Sub-Slab Depressurization System (SSDS) is the most prevalent method. It works by creating a negative pressure zone beneath the building's slab, which prevents radon from entering the indoor environment. This system uses a fan to extract radon gas from beneath 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 higher pressure inside the building compared to the soil outside. By introducing filtered outdoor air into the building, these systems prevent radon from seeping in. Positive pressure systems are frequently 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 mitigation systems:

• Building Use: multifamily units require a different approach versus single family or large commercial buildings.
• Foundation Type: The type of foundation (sub-slab, crawl space, basement, etc.) affects system design.
• Soil Composition: The type of soil (clay, sand, silt, etc.) impacts the effectiveness of different mitigation techniques.
• Additional Industrial Hygiene Requirements: Tasks such as asbestos or lead abatement may be necessary and can influence overall costs.
• Additional Trades/Hidden Fees – Electrician, Roofer, Permits, Aesthetic Options, Concealing Pipe Routing, etc.  

Although there is some flexibility in the design of radon mitigation systems, including choices like fan covers, the color of vertical riser piping, and occasionally the placement of the suction point, the fundamental design aspects—such as the number of suction points, fan size, and suction point location—are generally determined based on the radon mitigator's assessment of the factors above. In complex cases, a pre-diagnostic study may be required.