• cobylamarche


The principal source for indoor radon is soil and rock under and around the home’s foundation. Naturally occurring uranium in the soil/rock radioactively decays to radon gas. How does it get from out there, to inside? Principally through openings, both intentional and unintentional. Many homes are built with groundwater sumps; a proven technology to help keep basements dry, and a major entry point for radon. Utility entry points (water, gas, electricity, etc.) are also potential entry points for radon. Some basement drains are essentially open holes to the soil below the floor slab. Excellent in the event that the water heater leaks, not so excellent for radon gas intrusion. And of course, cracks. Whether spiderweb-looking shrinkage cracks, or cracks along intentionally cut control joints, these openings allow for the entry of radon. We also can’t forget the gap between the floor slab and the foundation wall. And these openings, while seemingly small, are a potential highway for radon transport.

The openings are just part of the radon intrusion problem. The other piece is gas flow. Where a basement is at a lower pressure inside than outside, the driving force for radon transport will be into the home. This depressurization can become exacerbated in the winter time where homes are closed and warm air inside the home is rising (stack effect). The rising warm air can cause soil gas (including radon) to be drawn in through the openings previously mentioned. Stack effect isn’t the only cause of depressurization. Bathroom fans, range hoods, and dryers all take air from inside the home and dump it outside. Moving air from inside to outside (without replacement) causes depressurization.

Gap between floor slab and foundation wall.

Great. So how do we fix it? Radon solutions will be the focus of upcoming posts.


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