Airborne radon mitigation is most often accomplished by the use of Active Soil Depressurization (ASD), otherwise known as Sub Slab Depressurization (SSD). This is a process whereby we bore a hole into the basement slab, and hollow out a pocket into the sub slab fill, which is called a suction point. Into this suction point, a PVC pipe is inserted vertically. We then seal around the pipe with urethane caulk. The pipe is routed from the suction point up to the roof line of the structure.  An in-line fan is connected to the pipe to draw sub slab radon bearing soil gas through the suction point, up through the pipe, and exhaust outdoors above roof line. If a home has multiple slab levels, suction points into each slab level will usually be needed. Oftentimes the pipes from multiple suction points are manifolded together and connected to a single fan unit, with a single exhaust.

ASD suction point

Suction point near water meter


Based on the structure’s layout, a system can be routed to the roof line either externally, through the interior, or through an attached garage. Sometimes all three route options are available within the same structure. Budget, aesthetics, future use, and expansion plans for the home can all play a roll in the final route option chosen. One system doesn’t necessarily work any better than another. It’s a combination of factors and considerations that will make one or two route options the better choice for a given structure. Our experienced certified National Radon Proficiency Program (NRPP) representatives can help guide homeowners to the best choice.

Illustration of ASD route options

Three general ways an ASD system can be installed in a home


The science behind ASD is to create a greater negative pressure under the slab as opposed to the negative pressure that exists within the structure. Once this is accomplished, radon bearing soil gas will no longer permeate up through the slab into the structure. ASD is the predominate radon in air mitigation tactic because it is highly effective at lowering indoor airborne radon concentrations, it is cost effective to install and operate, and has virtually no impact on heating and cooling costs. This process literally “intercepts” the radon before it ever has a chance to enter into the structure.

Exterior Route ASD on white house

Exterior Route ASD

CT Basement Systems Radon Inc. has successfully utilized ASD technology to mitigate airborne radon concentrations as high as 900 pCi/l. Contact us to schedule a no cost evaluation by one of our NRPP certified radon experts on how we can install an ASD system in your home or building at 1-800-319-8867.