How Radon Mitigation Works and Why It’s Important

Radon is a naturally occurring radioactive gas — colorless, odorless, tasteless, and completely undetectable without testing. It forms from the natural decay of uranium in soil and rock, and it seeps into homes through cracks in foundations, gaps around pipes, and other openings in the building envelope. Once inside, it can accumulate to dangerous levels.

The EPA identifies radon as the second leading cause of lung cancer in the United States, responsible for an estimated 21,000 deaths annually. It’s a serious public health concern, and it’s entirely addressable with proper mitigation.

How Radon Enters Your Home

Homes act like partial vacuums relative to the soil around them. The difference in air pressure between inside the home and the soil outside draws soil gases — including radon — inward through any available openings. This includes:

• Cracks in basement floors and walls
• Gaps around pipes, conduits, and utility penetrations
• Hollow block walls
• Construction joints in the foundation
• Sump pump openings
• Porous concrete itself
  
  

The rate of entry depends on the uranium content of local soil and rock (which varies significantly by geography), the pressure differential, and the number and size of entry points in the foundation.

Radon Testing

Testing is the only way to know if radon is a problem in your home. The EPA recommends testing all homes below the third floor, regardless of geographic location or building type.

Short-term tests (2–7 days) use charcoal canisters placed in the lowest livable area. They provide a quick reading but can be influenced by temporary conditions.

Long-term tests (90 days to a year) use alpha track detectors and provide a more accurate picture of average exposure.

The EPA action level is 4 picocuries per liter (pCi/L). Mitigation is recommended at this level and above. The average indoor radon level in the U.S. is 1.3 pCi/L; the average outdoor level is 0.4 pCi/L.

How Radon Mitigation Works

The most common and effective mitigation method is sub-slab depressurization (SSD), also called active soil depressurization (ASD).

The process involves:

1. Creating a suction pit beneath the slab floor by drilling one or more holes and excavating a small void
2. Installing a PVC pipe through the hole that connects to the exterior of the home
3. Mounting a continuously running fan to the pipe that draws air (and radon) from beneath the slab
4. Discharging that air outside, above the roofline, where it disperses harmlessly
   
   

By continuously drawing air from beneath the slab, the system reverses the pressure differential that was pulling radon into the home. Instead of radon being drawn in, it’s actively being pulled out and discharged outside.

A well-designed system reduces radon levels by 50–99%, bringing virtually all homes below the EPA action level.

Other Mitigation Approaches

Crawl space ventilation — Homes with crawl spaces may use active ventilation — fans that continuously exchange crawl space air with outside air — to dilute and remove radon.

Sealing entry points — While sealing cracks and gaps alone is rarely sufficient for significant radon reduction, it’s often done as a complement to active depressurization systems.

Basement pressurization — In some situations, positive air pressure in the basement can prevent radon entry. This is less common as a standalone solution.

Post-Mitigation Testing

After a mitigation system is installed, the home should be retested within 24 hours to verify the system is performing as expected. Ongoing testing every two years is recommended to ensure continued effectiveness, as system performance can change if entry points are sealed or structural conditions change.

Cost and Installation

Professional radon mitigation typically costs $800–$2,500 depending on the home’s construction and the system design required. Given the health implications, this is one of the higher-value safety investments available to homeowners. Most states have specific licensing or certification requirements for radon mitigation contractors — look for certified professionals through your state’s radon program or the National Radon Proficiency Program (NRPP).