Soil gas carrying radon is drawn indoors when air pressure in the house is lower than in the soil surrounding the foundation. Prevention and reduction of radon entry into the home is key to minimizing health risk and primarily done through Active Soil Depressurization [ASD], a method by which negative pressure is imposed on the soil around and under the home, reversing airflow and resulting in a suction effect to evacuate soil gas before it enters the home. Radon Resistant New Construction design [RRNC] is a passive approach to prevention and becoming more commonplace in American building practices. RRNC requires the installation of a pipe below the slab, traveling vertically through the conditioned space of the home and venting through the roof to the ambient air. Should this method be unsuccessful in reducing indoor radon levels, a fan can be easily attached to increase the suction effect and accelerate airflow. Homes built without RRNC design can be mitigated by retrofitting a similar system to the home either interiorly or exteriorly.
Regardless of the approach, the key to radon reduction by soil depressurization is to extend the negative pressure field under as much of the footprint as possible. Better yet is to extend the negative pressure field beyond the floor and up the perimeter foundation. To ensure year round reduction as weather changes alter the pressure levels inside and below the home, the negative pressure field should be stronger than the competing lowest interior pressures generated by the building [i.e. winter in the Northern United States].