What Is Sub Slab Depressurization?
Sub slab depressurization (SSD) is the most widely recommended and scientifically proven method for reducing radon gas in residential structures. Endorsed by the EPA, the World Health Organization, and the American Lung Association, SSD systems work by creating a zone of negative pressure beneath your home's concrete slab. This pressure differential prevents radon-laden soil gas from entering through cracks, joints, sump pits, and other foundation openings. Instead, the gas is captured below the slab and routed through a sealed PVC pipe to above the roofline, where it disperses safely into the outdoor atmosphere. In Cedar Rapids, where glacial till and limestone bedrock produce consistently high radon concentrations, sub slab depressurization is the method we install in the vast majority of homes.
How a Sub Slab Depressurization System Works
The system begins at the suction point, a four-inch hole cored through the basement slab. Beneath this hole, our technicians excavate a small cavity in the aggregate or soil to create an open pocket that allows airflow to extend outward beneath the slab. A sealed PVC fitting is inserted into the hole and connected to a vertical run of schedule 40 PVC pipe. This pipe is routed upward through the home, either through a closet, utility chase, or along an exterior wall, and exits through the roof or a sidewall above the eave line. An inline radon fan is installed along the pipe run, typically in the attic or on an exterior wall, and operates continuously at low wattage to maintain constant suction. The fan creates negative pressure across the entire sub-slab area, effectively intercepting radon before it can enter your living space.
Why SSD Is the Gold Standard for Radon Reduction
No other radon mitigation method matches the effectiveness, reliability, and long-term performance of active sub slab depressurization. When properly designed and installed, an SSD system can reduce indoor radon levels by 90% to 99%, often bringing concentrations well below 2.0 pCi/L even in homes that initially tested at 20 pCi/L or higher. The system operates around the clock with no action required from the homeowner, uses less electricity than a standard light bulb, and produces minimal noise. Unlike passive mitigation methods that rely on natural convection, active SSD systems provide consistent, measurable results regardless of weather conditions, wind patterns, or seasonal temperature swings. In Linn County's cold winters, when radon levels tend to spike due to the stack effect and frozen ground conditions, an active SSD system continues to perform reliably.
Every sub slab depressurization system we install in the Cedar Rapids area is custom-designed based on the home's foundation footprint, slab thickness, sub-slab material, and radon concentration. Some larger homes or homes with complex foundations may require multiple suction points to achieve full coverage. Our technicians use diagnostic pressure testing during installation to verify that the suction field extends across the entire slab, ensuring no dead zones exist. A U-tube manometer is installed on the system pipe for visual confirmation that the fan is operating, and a post-installation radon test is performed to document the reduction in levels.
Sub Slab Depressurization System Components
- Suction point cored through the concrete slab with sub-slab excavation
- Sealed PVC pipe (3" or 4" schedule 40) routed to above the roofline
- Inline radon fan rated for continuous 24/7 operation
- Exhaust point above the roofline for safe gas dispersal
- U-tube manometer for real-time system monitoring
- Fire-rated sealant at all penetration points
- Optional electrical indicator or alarm for fan failure notification
- Diagnostic pressure field testing to confirm full slab coverage
- Post-installation radon test to verify results below 4.0 pCi/L
- Written performance guarantee on every installation
- Licensed and insured technicians