Radon is a naturally occurring, invisible, and odorless radioactive gas formed from the breakdown of uranium in soil, rock, and water. It seeps into homes through foundation cracks, accumulating to harmful levels. Long-term exposure to elevated indoor radon is a recognized cause of lung cancer, ranking as the second leading cause overall and the primary cause among non-smokers. Radon mitigation systems are the primary solution for lowering indoor radon concentrations.
Understanding Radon Mitigation Systems
Radon mitigation systems reduce radon entry into a building or actively remove it. Active soil depressurization (ASD), also known as sub-slab depressurization (SSD), is the most widely adopted method. This system creates a negative pressure zone beneath the foundation, drawing radon gas from the soil before it infiltrates indoor air.
A sub-slab depressurization system involves several components. A hole is cored through the concrete slab, and a small pit excavated beneath creates a collection chamber. PVC piping extends from this point through the building, terminating outside above the roofline. An inline fan, placed in an unconditioned space like an attic or garage, continuously pulls radon-laden air from beneath the slab and vents it safely outdoors.
Other mitigation techniques exist for different foundation types. Sub-membrane depressurization, used in homes with crawl spaces, involves a high-density plastic sheet laid over exposed earth, sealed to foundation walls, with a fan and piping system creating negative pressure. Drain tile and sump pit depressurization utilize existing drainage systems or sump pits to collect and vent radon gas.
Measuring Effectiveness
Radon mitigation system effectiveness is determined through post-mitigation testing. This involves using short-term or long-term test kits after the system has been operational for at least 24 hours. The goal is to reduce radon levels significantly, ideally below the Environmental Protection Agency’s (EPA) action level of 4 picocuries per liter (pCi/L).
A picocurie per liter (pCi/L) quantifies radon gas concentration in a liter of air, representing radioactive decay. While no radon exposure is without risk, the EPA recommends corrective action when levels reach or exceed 4 pCi/L. Professionally installed mitigation systems are highly effective, capable of reducing indoor radon levels by 90% to 99%.
These systems can often lower radon concentrations to below 2 pCi/L. A study in Minnesota found 97% of homes with mitigation systems had post-mitigation levels below the EPA action level, with an average reduction exceeding 90%. While substantial reduction is expected, complete elimination of radon is rarely achievable due to its natural presence.
Factors Influencing Effectiveness
Several factors influence a radon mitigation system’s effectiveness. House characteristics, including foundation type (concrete slab, crawl space, or basement) and soil permeability, are important. The building envelope’s tightness, including cracks, pipe openings, and floor-wall joints, also impacts radon entry.
System design and installation quality significantly determine performance. This includes proper fan sizing, correct placement and sealing of suction points, and quality piping materials. Professional installation by a certified specialist ensures optimal performance and safety.
Sealing radon entry points is important. While sub-slab depressurization creates a vacuum, sealing visible cracks in the foundation, floor-wall joints, and utility penetrations enhances system efficiency by minimizing uncontrolled air leakage. A thorough assessment of these elements before installation contributes to a more effective solution.
Maintaining Effectiveness
Maintaining a radon mitigation system requires ongoing attention. Homeowners should regularly check the system’s manometer or pressure gauge. This U-shaped tube with fluid indicates if the fan is running and creating the necessary vacuum beneath the slab. If fluid levels are even, the fan is not operating.
Retesting radon levels is recommended every 2 to 5 years, or after significant home renovations. Major renovations, such as basement finishing or changes to ventilation, can alter air pressure dynamics and impact radon levels. Retesting confirms the system’s continued performance and identifies if adjustments or repairs are needed.
System maintenance involves keeping the fan clear of debris and routinely inspecting sealed entry points. Addressing new cracks or openings in the foundation also helps maintain efficiency. While systems are designed for continuous operation with minimal homeowner intervention, professional check-ups can be considered if there are performance concerns or if the fan reaches the end of its typical lifespan.