Radon remediation in 1832 bank home
Hi (and thank you in advance for any suggestions!) Turning to the experts as the radon mitigation companies we have spoken with are at a loss for solutions.
We own a historic home built in 1832 in eastern PA with plenty of stone for the foundation and walls. We recently realized that our radon levels are increasing throughout the bottom two levels of our home. A radon mitigation company has come out and installed a system with multiple pressure points in the basement and we were able to get the levels down to between 3 and 6 in the basement. So – not there yet for the basement level. Slab has no cracks but we have old stone foundation walls.
Additionally, the floor above the basement is half below grade with an entire wall of exposed stone/brick which sits against soil. (Photo attached.) The levels in this room are higher than the basement with an average of 7.9 over the past month (I have EcoQubes to monitor the basement and this space and have confirmed readings with charcoal 3-day tests.) This floor is a main living/sleeping space so very concerned.
We have had a number of radon mitigation companies out and they are mostly grasping at straws as to how to mediate to safe levels. We would prefer not to plaster or cover the exposed stone wall. Is an ERV an option? Are there ways to remove radon from the soil adjacent to the stone wall? I would be grateful for any/all suggestions! 🙏
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Replies
First, 3-6 pCi/L is hovering right around the EPA action level of 4 pCi/L. This is high enough you should work to reduce it, but not super high, so I wouldn't panic, but you do need to work to get those levels lower.
The easiest thing to do is likely more extraction points, especially close to that room of concern. Ideally, you want to depressurize the soil underneath the home evenly so that radon never enters the home at all. Sometimes one extraction point works, sometimes you need more. I'm going to assume you don't have a perimeter drain in place due to the age of the structure, so you don't have the option to tap into that for the subsoil portion of the system. You also don't want to seal that suspect wall, so an ERV would be the next option. You'd end up with a sort of two system setup, with the subsoil extraction system doing most of the work, and the ERV helping to keep things under control in the living space.
My preference for an "ideal" system would be to install a perimeter drain along the problem wall, then connect that to the radon extraction fan to depressurize the soil near the room that is partially below grade. My guess is you aren't getting negative pressure by the below grade wall in that room. Have any of the radon companies tested with a manometer to see if you're getting even negative pressure underneath the home? It's common for some areas to be better than others, which is why it's common to have more than one extraction point.
An ERV will help keep things under control in the living spaces by exchanging the indoor air with outdoor air. I'd still try to have the subsoil system doing the majority of the "work" of radon control though.
Bill
Bill - Many thanks for such a thorough and incredibly helpful reply!! We love the idea of a perimeter drain along the problem wall. It will take work but utilizes the existing system we now have. None of the radon companies have looked at pressure - but you can bet I am going to find someone who can test the pressure now. I think we might try the drain route first and go the ERV route if we can not get it under control. Again, many thanks - so helpful!! Michele