Weatherization and Radon Thanks for the responses. They all either confirmed my experiences or added to my knowledge.
Randy, you have more data than I have, but it conforms with my more limited experience. Sealing alone does not do much to reduce radon levels.
John and David, I agree with you about the beneficial effect of ASD on basement humidity. We have seen this reported over and over from customers. It would be interesting to see a study comparing the costs of ASD as a dehumidifying strategy versus dehumidifiers. Unfortunately, for the low-income weatherization industry, capital costs and budget limitations rule.
Gary, totally agree that " fat chance for reducing 8 pCi/L to > 4 pCi/L with passive efforts." I'm glad you mentioned the importance of stack effect.. The good news from the Wx front is that attic air sealing is an absolute priority in weatherization, and, as far as I know, is always done.I also know that basement duct sealing is done routinely. If return duct leaks predominate over supply duct leaks, than duct sealing should reduce basement radon levels (we've actually done return duct sealing in our private sector radon work). However, the national IAQ study, which measured radon levels before and after Wx work couldn't definitively conclude that Wx, which always included attic air sealing, significantly reduces basement radon levels. Part of this may be due to the fact that the buildings were also tightened so that natural ventilation was reduced.
There is some interesting research from Paul Francisco of the University of Illinois that increasing whole house ventilation, even using exhaust only ventilation (e.g. bath fans on timers), tends to reduce radon in the living spaces of homes slated for weatherization services.
It's all very complicated, but I hate to see Wx dollars wasted on measures that don't work.
Thanks.
Dick Kornbluth