How does soil gas radon get into buildings?

Soil gas radon enters structures through the openings in the foundation. The concentration found in any building is determined by several factors. These include concentration of gas in the soil, the permeability of the soil, and the amount of pressure differential there is between the soil and the building. Almost all buildings exert a negative pressure (suction) on the soil because of the natural stack effect and exhaust devices that exist in all buildings. The stack effect is the same phenomenon that occurs in a chimney. Hot air rises and leaves the top of the building. The replacement air is pulled in at the bottom of the building. This pull (suction) brings in the soil gas. Of the three factors (concentration, permeability, and pressure) the only one that can be controlled in an existing building is the pressure. If the pressure under the concrete slab can be made to be less than the building's pressure, the soil gas will no longer enter the building.

What is done to treat soil gas radon?

Sub-slab depressurization systems create a negative pressure under the slab that prevents the soil gas from being drawn into the building. To do this, pipes are inserted through the slab and routed to the exterior of the building. A fan is placed on the pipe and the exhaust is then routed to a safe area above the building. The fan pulls air from under the slab. Removing the air creates a negative pressure (suction) under the slab that is greater than the negative pressure (suction) exerted by the building. This negative pressure (suction) prevents the radon from entering the building.

The treatment for crawl spaces is similar to that for areas with slabs. In the case of a crawl space, a fire retardent plastic membrane needs to be laid down to provide the barrier the slab would normally create. Air is then drawn from under the membrane to create the negative pressure that prevents the entry of the gas.

Why use a registered contractor?

All radon system must meet certain minimum requirements to be safe. A registered mitigation contractor must comply with more than 140 regulations to install a system that meets the requirements set by the EPA. The average consumer will not know all of these requirements but should know some of the most crucial basics to make sure they are getting a safe reliable system.

Radon air and radon water fan mounted in garage attic

The Fan can not be below the living spacing.

Fan mounted on the outside of a house(click here for more photos)

The gas that is pulled from under the slab can have very high concentrations of gas (several 1000 pCi/L) and any leak on the pressure side(exhaust) of the fan can cause very high levels of radon to be released. This is why the fan should never be put in the basement. The are three common locations - literally outdoors, on the side of the building, in a garage or in the attic of the house.

The exhaust of the fan must be above the roof.

The release point must be in a location that will not allow it back into the structure being treated or into the neighboring structure. It also needs to be 2 feet above any potential reentry point that it is not at least 10 feet away from.

This is an example of a manometer(vacuum monitor) that measures the performance of the fan.

The system must have a monitor that will indicated the fan is operating properly.

This is not a radon monitor. It is a vacuum monitor to make sure the fan is creating and maintaining a negative pressure.

UL listed fire stop assembly in a garage

Garage wall penetration should be fire stopped with a UL listed system.

This is one of the most easily overlooked items that are found in many installations. The wall between all attached garages and homes is a fire rated wall and it integrity should be maintained.