How Radon Mitigation Systems Work and What They Cost in California

Sub-slab depressurization (SSD) is the most effective and widely used radon mitigation method, capable of reducing indoor radon levels by 50–99% in most homes. The system works by creating a pressure differential between the soil beneath the foundation and the interior of the home — drawing radon-laden soil gas away from the living space before it can enter through foundation cracks, openings, and porous materials. Installation in a typical Bay Area home typically costs $1,500–$3,500 and can be completed in a single day.

The system consists of a plastic suction pipe inserted through the slab or into the crawlspace membrane, connected to an inline radon fan that continuously draws soil gas upward and exhausts it safely above the roofline. Fans are low-power (20–90 watts) and run continuously. Most systems include a manometer (pressure gauge) in the pipe to visually confirm the system is maintaining proper pressure differential. System lifespan is 10–20 years, and fans can be replaced if they fail without reinstalling the full system.

Bay Area homes present some variation in mitigation approach depending on foundation type. Slab-on-grade homes use conventional sub-slab depressurization with one or more suction points. Crawlspace homes typically use crawlspace depressurization — a sealed polyethylene liner is installed across the entire crawlspace floor and a fan draws sub-liner air out through a pipe. Homes with both a slab and a crawlspace may require separate systems for each area. Basement homes (less common in the Bay Area) use sub-slab or sub-membrane systems depending on the basement floor construction.

Post-mitigation testing is essential. After system installation, we perform a follow-up radon test 30 days later to confirm levels have dropped below the EPA action level of 4.0 pCi/L. Most properly installed systems achieve levels of 1.0–2.0 pCi/L in Bay Area homes. If levels remain elevated, the mitigation contractor may need to add suction points, increase fan capacity, or address foundation bypasses allowing radon to enter around the system.

California does not have mandatory radon mitigation requirements for existing homes, but some counties are beginning to incorporate radon testing into building permit processes for new construction. The EPA recommends mitigation at any level at or above 4.0 pCi/L and considers action at levels between 2.0–4.0 pCi/L. In high-occupancy situations — such as schools, daycares, and long-term care facilities — action at 2.0 pCi/L is often recommended.