Passive Radon Mitigation System
Many new homes come with a builder-installed passive radon mitigation system. But unfortunately, frequently the answer to whether it is reducing radon levels to safer levels is an emphatic, “No.”
Due to the strength of radon gas permeating a home, even those perfectly constructed passive radon mitigation systems may not reduce levels sufficiently. We don’t even see many perfectly constructed radon systems!
In cases where a passive radon system isn’t reducing radon gas to safer levels (below 4 pCi/l), we install a radon fan on the vent pipe in the attic. This passive to active radon system effectively reduces radon gas levels in the home.
Want to Know More About Passive Radon Mitigation Systems?
Passive radon mitigation systems start at the bottom of a house. Sealed into the gravel layer under the basement slab or sealed into a sump cover which runs from the basement is a 3 or 4 inch PVC vent pipe. The pipe runs from the basement through the home and into the attic, ultimately venting through the roof.
A passive radon mitigation system passes the gas based on thermal stack effect. The greater the thermal difference and air density, the greater the buoyancy to drive natural ventilation. Basically, the house acts as a vacuum on the soil, where radon gas is emanating, due to temperature differences inside and outside the home.
The vent pipe should run through a combustion appliance chase (furnace or hot water heater) on its route from the basement to the attic of the house. The heat may create a vacuum for the radon gas inside the vent pipe, but ONLY if the following conditions exist:
1. The floor-to-wall joint and all other basement slab openings, such as sump crocks are completely sealed.
2. The vent pipe has no completely horizontal runs.
To convert a passive radon mitigation system to an active system is less than the cost of a completely new system, but it’s not possible in all cases. There needs to be at least three feet of accessible, vertical vent pipe in the attic.
Many builders make the mistake of sticking their vent pipe directly into the soil beneath the home, not properly venting it, or effectively blocking it from being useful. On top of that, they then vent what radon IS entering the pipe out the side of the home, sometimes at just above ground level where the radon gas can re-enter through windows and doors.
We implore you to test your house with a radon test kit. There is a very good chance that the passive radon system you have, that was installed by a builder, has not sufficiently lowered your radon gas levels.