- House Foundation Types
Your house type will affect the kind of radon reduction system that will work best. Houses are generally categorized according to their foundation design. For example: basement, slab-on-grade (concrete poured at ground level), or crawlspace (a shallow unfinished space under the first floor). Some houses have more than one foundation design feature. For instance, it is common to have a basement under part of the house and to have a slab-on-grade or crawlspace under the rest of the house. In these situations a combination of radon reduction techniques may be needed to reduce radon levels to below 4 pCi/L.
Figure 179: Your house type will affect the kind of radon reduction system that works best. Houses are generally categorized according to their foundation design.
Radon reduction systems can be grouped by house foundation design. Determine your type of foundation design and read about which radon reduction systems may be best for your house.
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: subslab suction, drain tile suction, sump hole suction, or block wall suction.
Figure 180: Active Subslab suction (also called subslab depressurization) is the most common and usually the most reliable radon reduction method.
Active Subslab suction (also called subslab 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.
A contractor usually gets this information from visual inspection, from diagnostic tests, and/or from experience. A radon vent fan connected to the suction pipe(s) draws the radon gas from below the house and releases it into the outdoor air while simultaneously creating a negative pressure (vacuum) beneath the slab. Common fan locations include unconditioned house and garage spaces, including attics, and the exterior of the house.
Passive subslab suction is the same as active subslab suction except it relies on natural pressure differentials and air currents instead of a fan to draw radon up from below the house. Passive subslab suction is usually associated with radon-resistant features installed in newly constructed homes. Passive subslab is generally not as effective in reducing high radon levels as active subslab 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 subslab 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 an be used in basement houses with hollow block foundation walls. This method removes radon and depressurizes the block wall, similar to subslab suction. This method is often used in combination with subslab suction.
An effective method to reduce radon levels in crawlspace houses involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors. This form of soil suction is called sub membrane suction, and when properly applied is the most effective way to reduce radon levels in crawlspace houses. Another less-favorable option is active crawlspace depressurization which involves drawing air directly from the crawlspace using a fan. This technique generally does not work as well as sub membrane suction and requires special attention to combustion appliance back drafting and sealing the crawlspace from other portions of the house, and may also result in increased energy costs due to loss of conditioned air from the house.
In some cases, radon levels can be lowered by ventilating the crawlspace passively (without the use of a fan) or actively (with the use of a fan). Crawlspace ventilation may lower indoor radon levels both by reducing the home's suction on the soil and by diluting the radon beneath the house. Passive ventilation in a crawlspace is achieved by opening vents, or installing additional vents. Active ventilation uses a fan to blow air through the crawlspace instead of relying on natural air circulation. In colder climates, for either passive or active crawlspace ventilation, water pipes, sewer lines and appliances in the crawlspace may need to be insulated against the cold. These ventilation options could result in increased energy costs for the house.