The process by which radon entry is controlled is referred to as mitigation. Radon can effectively be managed and reduced using methods specific to the building type. Active Soil Depressurization (ASD) is the most common method of mitigaiton. The three most common ASD mitigation types are: Sub Slab Depressurization (SSD), Sub Membrane Depressurization (SMD) and Block Wall Depressurization (BWD).
When it is not possible or practical to depressurize below or around a building envelope, other methods can be employed. This typically involves the installation of an Energy Recovery Ventilator (ERV) or Building Pressurization. For most structures, the best approach is to prevent the radon from entering. Sealing foundation joints and cracks is rarely sufficient as a standalone mitigation technique.
Sub Slab Depressurization is a relatively simple process. In the lowest level of the home, a hole (or holes) is cored in the concrete slab (typically in a corner or near the foundation wall) and soil and/or stone is removed through the cored hole. The exact location of a suction point cannot be determined until diagnostic testing has occurred. Piping and a small fan are installed to reroute the radon to the exterior of the house. The piping and fan are usually routed and installed in the garage or attic (if no living area above) or on the exterior of the house. Single suction points are effective in reducing the radon levels below 4.0 pCi/l most of the time. Multiple suction points may be more effective at reducing radon levels depending on the sub-slab conditions.
Most systems with a single suction point can be installed from $1,200 – $1,900. Some houses do require multiple cores and/or fans to adequately reduce the radon level which does involve a greater cost. Systems typically can be installed in one to two days.
Sub Membrane Depressurization is used in crawlspaces to control soil gasses (e.g., radon and moisture). A vapor barrier is added or improved above the ground in the crawlspace. Piping and a small fan are used to reroute the radon laden gas from underneath this vapor barrier to an outside vent on the top of the house. This type of system has recently been proven effective in reducing and controlling moisture levels in crawlspaces that can contribute to indoor air quality and mold problems. The cost of these systems is dependent on individual conditions of the space.
Block Wall Depressurization is used to control soil gasses from entering a basement through cement block walls. Small holes are drilled into the block wall to allow the vent connection. All visible and accessible openings or penetrations in the block wall are sealed to prevent air loss from the basement area. Piping and a small fan are installed to reroute the radon to the exterior of the house. The piping and fan are usually routed and installed in the garage or attic (if no living area above) or on the exterior of the house. If the block wall foundation does not have a cap block or the top cells of the block are open, they must be sealed prior to installation of the system.
Energy Recovery Ventilators are used in the process of exchanging indoor air with outdoor air to dilute the radon levels in the home. The greater the amount of air exchange, the lower the radon levels will be. Because there is warm humid air outside, it is necessary to pre- condition the incoming outdoor ventilation. The benefit of using energy recovery is the ability to meet the ASHRAE ventilation & energy standards, while improving indoor air quality, and reducing total HVAC equipment capacity requirements.
Building Pressurization is fairly difficult to maintain, and is less commonly used as a mitigation approach. The EPA recommends that a qualified contractor be used to mitigate homes due to the specialized technical experience required. Without proper equipment or technical knowledge, one could actually increase the radon levels or create other potential hazards.