How does a radon mitigation system work?
• A sub-slab depressurization system works by bypassing the negative pressure inside a house, using a continuous air channel that runs from the area beneath the basement slab or sealed crawlspace vapor barrier up to and through the finished roofline. This air channel usually consists of the largest diameter PVC piping that will fit inside of a finished wall (usually a 3-inch inside diameter). Somewhere along this piping will be a continuously running, electrically driven fan that creates a negative pressure in the sub-slab area and pulls the radon-contaminated air through the house without it getting into the breathable air. A common place for the radon exhaust pipe to be installed is in the sump pump pit. If there is no sump pump pit in the basement area, a section of the basement slab will have to be removed for the bottom of the pipe to be installed.
The most common radon system is a sub-slab depressurization system. A fan, located in an attic or outside the building, is used to draw air out from under a basement, crawl space or slab on grade concrete slab. If done properly, the entire area directly below the slab becomes negative in pressure as compared to the air above the slab. This causes the normal airflow out of the soil to reverse and flow into the soil, which effectively stops all infiltration of radon laden soil gas. The sub-slab depressurization system needs to create this sub-slab negative pressure under all slabs that are contributing a significant amount of radon into the building. Refer to mitigation system explanation for a more detailed description and system drawings. See mitigation system photos.
Radon typically enters a structure due to a pressure differential between the negative pressure of the interior space and the positive pressure of the exterior surrounding soil. A typical radon mitigation system uses a fan (located in an attic or outside the building) to draw air out from under the concrete slab or crawl space. If the system is designed correctly, the exterior surrounding soil will be under negative pressure compared to the interior space. This process will stop the infiltration of radon gas into the structure.
