RADON MITIGATION

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How does mitigation work?

Active Soil Depressurization (ASD) is a fancy term for Radon Mitigation System.


A building creates negative pressure beneath itself that can force radon gas into the dwelling. What a mitigation system does is depressurizes the soil below the structure’s slab or vapor barrier by vigorously pulling air/gas from a suction point through a 3-4” PVC pipe, and expels it above the structure’s roof-line. This reduces the concentration of radon gas in the dwelling by pulling it through the pipe like a tunnel or a straw, and not allowing the gas to get trapped inside the structure.


This is achieved through the steps that follow:

1. A Radon Technician will seal all the cracks in the foundation that are accessible. This creates a more “air-tight” seal on the foundation slab for the system fan to pull from.

2. The suction hole is drilled into the foundation and a pit is excavated. This allows the system fan to pull air from under the slab of the structure.

3. Test holes are drilled in various slab locations. These small test holes allow the technician to verify that the fan is drawing suction from various locations in the slab.

4. A hole is drilled to run the piping to the exterior of the structure.

5. The fan is installed, and piping is routed above the roof-line, as per DEP guidelines.

6. After the system is activated, the technician verifies suction at test holes and a follow up radon test is administered.


This system is set up to provide a constant draw of gases from under the slab. These sub slab gases are pulled from under the slab and the radon fan extrudes these through piping above the roof line. 

Is there more than one type of Radon Mitigation System?

Yes, there are 3 types of systems. Depending on the results of the diagnostic testing, one of the following 3 systems would be installed.


• INTERIOR – This system starts in the basement or the garage of the structure. The exhaust piping is run through closet(s) to the attic where the exhaust fan is placed, and exhausted through the structure’s roof. The entire system is run through the interior of the structure, except for the exit point in the structure’s roof. A monitor is then placed near the vent line in the basement or closet area.


• GARAGE – This system also begins in the basement and the pipe is run through the rim joist into the garage, and vertically along the garage wall into the garage rafters or attic (if there is one), through the dwelling roof-line. The monitor is attached to the vent line in garage or basement area.


• EXTERIOR – With this system it begins in the basement. The vent pipe is then routed through the rim joist of the foundation wall to the exterior of the dwelling. The fan is placed at ground level and the pipe then runs vertical along the side of the structure and is exhausted above the roof line. The monitor is attached near the vent line in the basement or outside at ground level. The nice thing about this system is the pipe can be boxed in or painted or aesthetic appeal.

How do you know the system is working?

A U-tube manometer is connected to the system to ensure the system is working properly.


A U-tube manometer is a U-shaped tube filled with liquid; it’s a device that measures two different gas pressures against each other and the power of the captured gas.


If the liquid is equal of both sides of the tube, the system is NOT functioning properly.


The liquid should be different levels on each side. This indicates that the system is functioning properly.