Mitigation Systems

Radon Mitigation Systems


Radon is a naturally occurring gas that is produced by the decay of uranium in rock and soil. It becomes a health hazard when it is trapped below and around the foundation of a building and enters the structure though openings in the slab or basement walls.

In most cases, the best approach to radon mitigation is a form of depressurization. This radon mitigation strategy involves creating a negative pressure field below the building foundation to draw gas from the underlying soil and exhaust it safely above the roofline. The objective is to design a well sealed system with an extensive negative pressure field using a fan as suction. Construction characteristics of the building direct how this can best be achieved. Mitigation professionals will consider the type of foundation, the size of the house, the radon level, the existence of structural additions and drainage systems among other things in prescribing the best mitigation plan for a home.

The technician will inspect the basement area for any openings that may impact the effectiveness of the system. Openings and cracks in the foundation will need to be closed or sealed. Open sump pumps or floor drains can impact the effectiveness of the radon mitigation system and can also serve as significant entryways for radon. Sump pits will be sealed and floor drains may need a one way valve installed to improve system function.


When installing a sub-slab depressurization system, a radon collection chamber must be created below the slab. The technician will determine the best placement for the system, then drill a hole through the slab to accept the radon collection piping. Approximately ten gallons of soil will be removed to establish the collection pit.

A four inch radon collection pipe will be fitted and sealed into the slab opening. The piping will then be routed to the exterior of the house just above grade. A radon fan will be mounted to the system with the discharge stack continuing up along the side of the house and extending above the roofline. A system disconnect will be wired to an existing available circuit with waterproof conduit.

In some cases, a single suction point is inadequate to extend negative pressure below the entire foundation. This may occur in areas of tight or compacted soil. Interior footers for home additions and other construction elements may also impede the effectiveness of the system. In these situations, an additional suction chamber is required. Additional chambers are located where they can best extend the collection field. These chambers are tied into the original discharge pipe and are driven by the same fan. This configuration will be recommended when radon levels are high, or when a technician determines that a single suction system will be inadequate to mitigate due to soil, or construction characteristics of the house.


Many new homes are being constructed to be “radon resistant” with passive radon systems built in. These systems involve a single straight pipe running from a radon collection chamber below the foundation, through all floors and exhausting through the roof. Passive radon systems are installed during initial construction. These interior systems work on a “chimney effect” where rising warm air draws radon from below the foundation up and out of the house.

These systems are often inadequate to move the amount of radon collecting below the foundation. IT IS VERT IMPORTANT THAT HOMES WITH PASSIVE SYSTEMS BE TESTED FOR RADON.

When a passive system fails to keep radon levels below 4.0 pCi/L, the system should be activated. System activation involves an inspection of the radon collection chamber and assuring that the exhaust pipe has penetrated the roof. The technician then mounts a radon mitigation fan to the existing discharge piping in the attic of the home. The fan will be wired to an existing electrical circuit located in the attic.

In some situations, activating the system is still insufficient to remove all the accumulated radon from below the foundation. If this occurs, an additional collection site will be recommended to extend the collection field. The second suction point is tapped into the original system and driven by the same attic mounted fan.


A garage attic installation provides a “hidden option” for a radon mitigation system. This option can be considered for homes with an attached garage with unconditioned attic space. A standard sub-slab depressurization system is installed in the basement of the house. The vent piping penetrates into the ground level of the garage and then runs up into the garage attic and penetrates the roof. The radon mitigation fan is mounted to the system in the garage attic space. The fan will be wired to an existing electrical located in the attic.


This type of installation applies to homes that are built on a slab on grade (have no basement foundation). An interior or an exterior approach can be taken to this installation strategy.

An interior installation can be used in a single story slab foundation home. The technician will look for a suction chamber location within the home in a utility room or closet. The suction chamber is created by drilling an opening in the slab and digging out a radon collection pit. In a single story home, the vent piping can be run straight up into the attic area and vented through the roof. The radon mitigation fan is mounted to the system in the attic and wired to an existing electrical circuit near the fan location.

A second suction chamber can be added in the case of a single story home. An additional suction pit would be created with the vent pipe also extending into the attic. The two suction locations would be connected via piping in the attic and are driven by a single radon mitigation fan.

In a multilevel home slab foundation home, a collection chamber would be created inside in a utility room or closet with an exterior wall. The vent pipe would exit the home through a wall penetration and the fan would be mounted outside the house with the discharge stack extending up the side of the building, safely above the roofline. The fan will be wired with a system disconnect switch to an existing available circuit.

In some instances, there is no acceptable interior location to create a radon collection chamber. In these situations, the technician will gain access below the slab by excavation and penetrating the foundation footer. Soil must be removed from beneath the slab to create the radon collection pit. The radon vent pipe will be inserted into the pit and sealed. The pipe will then be directed up along the side of the house to above the roofline. The radon mitigation fan will be mounted to the system just above grade and wired to an existing available circuit.


A crawlspace with exposed dirt or gravel can be a significant contributor to radon in a home. The crawlspace must be addressed to ensure successful mitigation. In homes with small crawlspaces, sealing the crawl with a vapor barrier is combined with the installation of a sub-slab depressurization system. However, if the majority of the house is over a crawl, then a depressurization system needs to be installed in the crawl area with the vapor barrier. The sealed space serves as the radon collection chamber.

Radon collection piping is installed in the crawlspace and covered by the vapor barrier. The barrier is sealed at the foundation walls, around the radon pipe penetration, and around any other vertical pipes or supports. The radon vent pipe exits the crawl to the exterior of the house and is directed up along the side of the house extending above the roofline. The radon fan is mounted to the system just above grade and is wired with a disconnect switch to an existing available circuit.

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