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How do you improve an old block foundation with no insulation or exterior moisture barrier?
March 11, 2021, 4:19 p.m.
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We get a lot of people asking about the best way to insulate a cinder block (CMU) foundation wall, I would say the first place to go is this discussion here which I think already answers all your questions -
How to insulate a cinder block foundation wall properly
If you don't find all you need in there let me know with a follow up question. And where are you located? The severity of the climate you live in will play a big factor in how you want to proceed, cinder block foundations in cold climates are trickier than warm ones. Find your climate zone here on this page.
Thank you so much Mike. I am in Vermont. Sometimes it goes below 0F for weeks. Gave insulating exterior walls, but can only excavate about 50% of foundation due to concrete stairs and platforms around the exterior. Not really sure what to do at this point. Read many conflicting recommendations and opinions on-line while researching this topic. I was reluctant to insulate from the interior for the reasons you mentioned. House is an all block house including foundation and interior of basement is about 820SqFt. I appreciate your input but am still not sure where to go with this. ANy other advice is welcomed.
Given there are a few issues it may be best to address them one at a time. On moisture - does it flood or is it just high humidity? If you get bulk water then you would be wise to install a drain. If it's not a finished floor then you could smash the concrete with a sledge hammer around the edge , dig it out and intall a drain. If its about high humidity then I'd run a dehumidifier.
Forgetting about insulation for the moment, you could at least stick a 6 mil poly vapor barrier on the walls if that's where the moisture issue is coming from. If it's a poured concrete floor and it has no vapor barrier beneath then that will for sure be a source of moisture, but a dehumidifier will help with that and we can cover that after. I hesistate to recommend interior insulation without physically seeing the wall, but the poly won't do you any harm. It will help prevent mold, and it will help with heating costs a bit since it will keep it drier heating moist air consumes a lot more energy than heating dry air.
Give us more details though - Ceiling height, finished walls or not (is it living space), poured concrete floor or not, flooding, moisture levels, mold or no mold, etc, whatever you can tell us will help us help you pick a solution.