03/02/2026
a detailed technical cross-section diagram of a Radon Mitigation System (specifically an active soil depressurization system) installed in a residential building with a basement and an accessible attic.
The diagram outlines the specific components, materials, and code requirements necessary to safely vent radon gas from beneath a home's foundation to the outdoors.
1. SUB-SLAB & BASEMENT COMPONENTS (THE SUCTION POINT)
At the lowest level, the system focuses on capturing radon gas before it enters the living space.
🔸 Gas-Permeable Layer: A minimum of 4 inches of clean gravel is placed under the slab to allow gas to move freely toward the suction pipe.
🔸 Soil-Gas Membrane: A polyethylene or cross-laminated membrane (v***r barrier) is laid over the gravel. The diagram specifies a 12-inch overlap at the seams to ensure a tight seal.
🔸 Piping & Connections: The system uses 3-inch or 4-inch ABS or PVC pipe. A "Tee fitting" connects the vertical vent stack to the perforated drain tile system or a sump pit.
🔸 Sump Pit: The diagram shows the vent pipe integrated with the sump pit, which is a common collection point for sub-slab gases.
2. THE VERTICAL VENT STACK (THE PATH)
The pipe travels vertically through the "First Floor" and into the attic.
🔸 Labeling: For safety and identification, a Radon Gas Vent System Label is required on every story of the house, as well as in the attic and crawl spaces.
🔸 System Failure Warning Device: Located on the first floor, this is a manometric or electronic alarm that alerts the homeowner if the fan stops working or if pressure is lost.
3. ATTIC & EXHAUST COMPONENTS (THE EXTRACTION)
The "active" part of the system is housed in the attic to ensure that any leaks in the pressurized portion of the pipe occur outside the living space.
🔸 In-Line Fan: An approved fan is mounted in the attic. The note specifies that the fan cannot be installed in crawl spaces, basements, or living spaces to prevent radon from leaking back into the home under positive pressure.
🔸 Flexible Couplings: These connect the fan to the PVC pipe, helping to reduce vibration and noise throughout the house.
🔸 Electrical Requirements: A dedicated electrical circuit is extended to a junction box, and a switched luminaire (light fixture) must be provided near the fan for maintenance.
🔸 Insulation: Pipes in unconditioned spaces (like the attic) must have R-4 insulation to prevent condensation from freezing and blocking the pipe.
4. ROOF TERMINATION (THE DISCHARGE)
🔸 Vertical Clearance: The pipe must terminate at least 12 inches above the roof surface.
🔸 Horizontal Clearance: The exhaust must be at least 10 feet away from any openings into the dwelling (windows, doors, or vents) to prevent radon from re-entering the home.
