Where do you put a vapor barrier on a cinder block foundation?
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How do you apply vapor barrier and insulation to a CMU house?
Scott Brekke
Nov. 22, 2019Last updated: Aug. 27, 2020
This house is located in SC and is built with 8" block walls. What is the best way to insulate and apply vapor barrier. I have to install studs to the interior of the block for seismic resistance and attach the studs to the block. The block walls will basically become a veneer. Can I apply a paint vapor barrier, and which side of the block should I apply it to?
Foundation made of CMUs (aka Cinder block foundations), are trickier to fix than poured concrete foundations. They are not nearly as strong since it is only the mortar between blocks that holds them together, so freezing can cause problems.
We’ve yet to see one that really knocked it out of the park in terms of durability and moisture management, so chances are yours has no exterior membrane, is that correct? Either way, your first step would be to check out this forum page here that already discusses the issue:
How to insulate a concrete block foundation
Granted, that cinder block foundation repair technique is for a slightly colder climate, but that just makes it a bit easier on you, and the science behind the moisture movement is the same.
Is there any efflorescence (moisture stains) on the walls? South Carolina can have a bit of a range of climate zones, so exactly which part are you in? You should also check out this page on how to prevent mold when finishing basements , that’s one of our building guide pages that will help you pick a method. Read those over and get back to us, we can for sure set you up. Sound good?
@Scott Brekke, did you ever resolve this situation? If I'm reading your comment correctly, you weren't referring to the foundation, but the actual (above-ground) house that is built out of CMU's or maybe even Rock Face Block. I am facing the same exact dilemma in NE Tennessee. High humidity, 40 degree winters, 90 degree wet summers. Mold on the interior of the concrete block but since it is rock face, that IS the siding so I have to build the layers on the interior. What did you end up doing, if you don't mind sharing?