Let’s start with the entry points of water and radon for radon systems. Radon is a soil gas. Aside from contaminated building products or aggregates, almost all radon enters the home from the soil. Radon’s half life is a little under four days. That means if you had a small known quantity of radon, it could disappear within a few weeks. The problem is: radon is a decay product from the Uranium 238 decay chain. Uranium is plentiful and it’s found in bedrock around the globe. Radon and its decay products are constantly being produced, so there is a near infinite supply that is percolating up from the ground at any given time.
Ground water can drastically affect the amount of radon that enters or is forced into a home. For example, heavy rains can raise the water table. Water replaces soil air. This causes a hydraulic push of soil air up into the home. It also inhibits the amount of air that can be removed from the system by a radon fan. This is why you’ll often see an increase in your u tube manometer readings after heavy rains—or why your KTA meter moves to the red left after big storms.
You cannot pull radon through water with a radon fan. Water vapor and moisture can cause significant damage to homes. It’s no surprise that they can do the same to radon systems. If the water table on a home is within a few feet of the slab or crawlspace, then it’s imperative that you fix your water issue before you start on your radon issue. Homes with high water tables need to have a professional install a sump or dewatering system. Any radon system installed before dewatering will almost certainly not work in all seasons and weather conditions.
Again, you cannot pull radon gas through water with a radon fan. This is why sloping your radon piping is paramount. If you create any traps in your sub soil depressurization system, then you’re bound to hear water bubbling or gurgling. Soil air is warm air. The air under your home is a constant 50-60 degrees in North America. When the air outside your radon system is higher than that, then you get condensation inside the radon piping. I call it the “reverse pop can effect” (or soda can for those of you not from the Midwest). Even if your soil air is extremely dry and your climate is dry, you can still have tremendous amounts of condensation build up inside a system. You must slope all the PVC to the extraction point, or risk water traps and noisy bubbling sounds.
The same goes for your sub slab or sub membrane collection. This is why you cannot run geotextile soil gas collector mat down trenches or up and down different building elevations. Any sub floor collection system needs to be level or your risk water traps. Water traps mean you lose PFE and your radon system stops functioning.
With all the moisture in soil air, it’s important that you buy a real radon fan. Read about proper fan moisture protections here. True radon fans can exhaust up to 15 gallons of water vapor per day. Fans not rated for moisture will fail within days or weeks. That’s an ancillary benefit to a well-designed radon system. I’ve known many builders that activate all radon ready systems–even those where high radon is not found. They find that a 20 watt radon fan prevents water under the slab and keeps musty smells out of their brand new homes.
Anecdote incoming: when we built my sister’s radon system, we had a big surprise. She lives in a flood plain on the front range of Colorado. Her house was built in the 1960s. Within thirty minutes of turning on the radon fan she comes running upstairs shouting that the musty basement smells are gone. Yes, her KTA radon fan got rid of so much water that it cleared up her “old basement smell” before we could finish our “job well done” beers. She thought she was trapped with old home smell, turns out all she needed was a radon system.
As you can see, water affects radon system function and radon levels dramatically. This is why long term testing is so important. A dry foundation is a healthy foundation. Be sure that all required dewatering systems are operating before you build a radon system. After that, slope all PVC toward the extraction point, and let your radon fan take care of any left over condensate or water vapor.
Thanks for reading!
