A) Sub-Slab Soil Depressurization [SSD] or Active Soil Depressurization [ASD]
The most common radon control and reduction technique designed to achieve lower sub-slab pressure relative to indoor air pressure by use of a fan-powered vent drawing air from beneath the concrete slab. When powered by a fan, these systems are called Active Soil Depressurization [ASD]. The fan’s velocity creates suction below the foundation and vents radon gas and its byproducts into the ambient air, typically to an area the above the highest eave of the house. Pipe routing may be interior or exterior and the discharge point must be high enough to prevent re-entrainment.
B) Sub Membrane Depressurization [SMD]
Sub Membrane Depressurization is performed in crawl spaces and areas that are directly in contact with rock or soil. Suction is created under a specified polyethylene or equivalent flexible material (plastic sheet) permanently installed over exposed soil or rock. A fan drawing radon from beneath the plastic sheet exhausts the radon outdoors above the highest eave of the house.
C) Drain Tile Depressurization [DTD]
Drain Tile Depressurization means a type of active soil depressurization system where the suction point piping attaches to a drain tile or is located in the gas-permeable material near the drain tile. The drain tile may be inside or outside the footings of the building.
D) Block Wall Depressurization [BWD]
Block Wall Depressurization means a radon mitigation technique that depressurizes the void network within a block wall foundation by drawing air from inside the wall and venting it to the outside.
E) Crawlspace Depressurization [CSD]
Crawlspace depressurization is not ideal due to the great potential for hazardous back drafting and high energy loss associated with its operation during the colder and hotter months. Sub-slab and sub membrane depressurization are the crawlspace mitigation methods that should be used whenever possible.