How Radon is Mitigated
You will never find a level of ZERO in any radon test. Even outdoor air typically has 0.2 to 0.7 pCi/L of radon. However, when a home or building is found to have radon levels that can be considered hazardous, action can be taken to reduce it to acceptable levels. There are several methods that can be used to permanently correct this problem.
The most common approach is what is known as "Active Sub-Slab Depressurization" or (ASSD). This method involves drawing the radon gas (and other pollutants) from the soils that are directly adjacent to the structure. In order for this method to be effective, a sealed barrier between the home and the soil must be available to divert the radon gas away from the home.
In a home with a basement, the concrete slab acts as a barrier between the home and the soil. In this case, a PVC pipe penetrates the slab through a hole in the slab that is created with a coring drill. A void is created between the slab and the soil which allows the radon gas to collect. A pipe is then inserted into this void area and a suction fan is installed. The radon becomes pressurized and is drawn into the system to be safely released into the atmosphere.
Homes with exposed dirt or gravel crawl space areas can be mitigated by “Active Sub-Membrane Depressurization” or (ASMD) which involves the use of a radon retardant membrane to seal the floor of the crawl space area. A pipe penetrates the membrane and a suction fan is installed. The radon becomes pressurized, is drawn into the system and exhausted into the atmosphere.
Homes with a basement and a crawl space (concrete, dirt or gravel) will require a combination of these methods.
99% of all radon problems can be corrected by use of Active Sub-Slab/Membrane Depressurization. This is the preferred method of radon mitigation since it primarily involves extracting radon gasses from beneath the home’s foundation (which is the air from soil, or “dirty” air.) Since these systems are designed to avoid the loss of “conditioned” (heated or cooled) air from the home, they have very little impact on the efficiency of the home.
“Skeletal New Construction Systems” (SNCS) or “Passive Radon Reduction” are installed during the construction process of a new home. They are designed for the future installation of a vent fan and may consist of multiple vent pipes, vertical and angled runs, routed from the suction pit to at least 12 inches above the roof. If you are planning on buying or building a new home, tell your contractor you want a Passive Radon Reduction System designed into the house plan.
The most important thing to realize is that a radon problem can be corrected in any home. A home with a radon mitigation system will consistently have radon levels well below the average American home regardless of how high the radon levels were prior to mitigation.