Radon Mitigation System
Radon mitigation is any process or radon system used to reduce radon concentrations in the breathing zones of occupied buildings and homes. The goal of a radon mitigation system is to reduce the indoor radon levels to below the EPA action level of 4 pCi/L. A quality radon reduction (radon mitigation) system is often able to reduce the annual average radon level to below 2 pCi/L. In general, costs can range from approximately $800-$2500, with the average reduction system costing approximately $1500.
The PBS series “Ask This Old House” visited a home in Minneapolis to install a radon mitigation system. The episode covers how radon reduction systems are properly designed and installed. This video gives the viewer a good sense of what to expect from a radon mitigation professional and radon reduction system.
Properly designing and installing a radon mitigation system is a professional level activity. This will ensure the final system is properly located and sized to achieve optimal radon reduction and not cause any other potential issues with the structure. Only radon mitigation professionals on the MDH list should be hired to do radon mitigation. Be certain the individual hired visits the jobsite prior to beginning any work to give you a solid proposal for radon mitigation. Also make sure the certified individual will be on-site doing the work on your house.
Due to the recent increase in radon testing in Minnesota, consumers need to be aware of uncertified individuals conducting radon-related work. Be aware of uncertified installers and inexpensive radon mitigation rates (less than $1,000). Price quotes promising really low installation rates are often too good to be true and leave the consumer with sub-standard workmanship and materials and a radon mitigation system that may not be working. Be sure to get a firm price and avoid hidden fees for future work when it may become necessary. Also, do not pay for the system in full before the work is complete. A valid radon test showing reduced levels should be obtained prior to full payment.
Foundations
Diagram of multiple foundation types
Any home can have a radon problem, no matter what type of foundation it has.
Basement: provides a large surface area in contact with soil material. Radon can enter through cracks in the concrete, or through floor-to-wall joints or control joints. Since many Minnesota homes use their basements as living space, exposure to radon gas can be further increased. But radon gas can enter a home regardless of whether or not there is a basement.
Slab-On-Grade: Slabs built on grade can have many openings that allow radon gas to enter, just as in a basement.
Crawl Space: Homes with crawl spaces can also have elevated radon gas levels. The vacuum effect can draw radon gas from a crawl space into the home.
Manufactured Homes: Unless these buildings are placed on supports without skirting around them, interior air pressure vacuums can cause radon to enter manufactured homes, as well.
Suction System
The are four types of soil suction systems: sub-slab, drain tile, sub-membrane and block wall.
diagram of sub slab radon mitigation system
Active sub-slab suction: (also called the sub-slab depressurization, or SSD) is the most common and usually the most reliable system because it draws radon-filled air from beneath the house and vents it outside.
Passive sub-slab suction: is the same as active sub-slab suction, except not as effective. It relies on air currents instead of a fan to draw radon up from below the house.
Drain tile suction system: caps are placed on the sump pump baskets. The pump continues to drain unwanted water.
Block wall suction: systems are used in homes with hollow block foundations by using a system similar to the sub-slab suction, where radon is removed from the wall by depressurization.
10 Step Process
Radon Testing
Homeowners radon test reveals the home has high radon levels (elevated radon gas).
Homeowner contacts certified mitigators to request bids.
Contractor does a walk-through of the home to identify problems then outlines the mitigation system they recommend.
Homeowner reviews key questions with each contractor requesting a proposal bid and references.
Homeowner evaluates and compares contractor recommendations, bids and contracts, selecting the contractor and scheduling the work.
Contractor may perform diagnostic testing to ensure proper size and installation methods are applied.
Contractor seals required areas, e.g., large cracks, crawl spaces, sumps, etc.
Contractor installs the mitigation system, i.e., suction pit or ventilation, pipe routing, etc. Electrical hook-up completed by licensed electrician, not a licensed contractor.
Contractor provides full explanation of system’s operation to homeowner.
Homeowner or contractor test the home to ensure the system is reducing radon to the desired level.
Other methods to Reduce radon levels
Other radon reduction techniques may be considered to reduce the radon gas levels that are circulating within the home. Many of these methods are used only as temporary measures, or in combination with other measures, like the ventilation or suction system.
Ventilation: can sometimes lower indoor radon levels in crawl spaces by reducing the home’s suction on the soil and by diluting the radon beneath the house. Passive ventilation is achieved by opening or installing vents. Active ventilation uses a fan to blow air through the crawl space. To be effective, ventilation is often used with sub-membrane depressurization, which covers the dirt of the crawl space floor with a plastic sheet. A pipe then draws the radon air from under the sheet to the outside.
Sealing: cracks and openings in the foundation is a basic step in radon mitigation. Sealing will limit the flow of radon, making other mitigation techniques more efficient. This is a temporary measure because normal settling of a home opens new entry routes and reopens old ones.
Pressurization: uses a fan to blow air into the lower level of the home, creating enough pressure to prevent radon entering. To maintain enough pressure, doors and windows at the lowest level must not be left open.
Heat recovery ventilator (HRV): (also called an air-to-air heat exchanger) is used to increase ventilation in all or part of a home. The HRV introduces outdoor air by using the heated or cooled exhausted air to warm or cool the incoming air.
What to look for in an installed system
Radon reduction (radon mitigation) systems must be clearly labeled. This will avoid accidental changes to the system which could disrupt its function.
The exhaust pipe(s) of soil suction systems must vent above the surface of the roof and 10 feet or more above the ground, and at least 10 feet away from windows, doors, or other openings that could allow the radon to reenter the house, if the exhaust pipe(s) do not vent at least 2 feet above these openings.
The exhaust fan must not be located in or below a livable area. For instance, it should be in an unoccupied attic of the house or outside — not in a basement!
A warning device must be installed to alert you if an active system stops working properly.
A post-mitigation radon test should be done no sooner than 24 hours after your system is in operation with the fan on, and last at least 48 hours.
Attached written operating and maintenance instructions and copies of any warranties.
Source: Minnesota Department of Health
A 3″ PVC pipe is run out of the crawlspace, into the basement and to a suction pit under the basement floor. The 3″ pipe will allow the increased pressure in the system to draw as much radon as possible to the suction point.
