Basement and Slab-on-Grade Houses
In houses that have a basement or a slab-on-grade foundation, radon is usually reduced by one of four types of soil suction: sub-slab suction, drain tile suction, sump hole suction, or block wall suction.
Active Sub-slab suction (also called sub-slab depressurization) is the most common and usually the most reliable radon reduction method. One or more suction pipes are inserted through the floor slab into the crushed rock or soil underneath. They also may be inserted below the concrete slab from outside the house. The number and location of suction pipes that are needed depends on how easily air can move in the crushed rock or soil under the slab, and on the strength of the radon source. Often, only a single suction point is needed.
Passive sub-slab suction is the same as active sub-slab suction except it relies on natural pressure differentials and air currents instead of a fan to draw radon up from below the house. Passive sub-slab suction is usually associated with radon-resistant features installed in newly constructed homes. Passive sub-slab is generally not as effective in reducing high radon levels as active sub-slab suction.
Some houses have drain tiles or perforated pipe to direct water away from the foundation of the house. Suction on these tiles or pipes is often effective in reducing radon levels.
One variation of sub-slab and drain tile suction is sump hole suction. Often, when a house with a basement has a sump pump to remove unwanted water, the sump can be capped so that it can continue to drain water and serve as the location for a radon suction pipe.
Block wall suction can be used in basement houses with hollow block foundation walls. This method removes radon and depressurizes the block wall, similar to sub-slab suction. This method is often used in combination with sub-slab suction.