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interior insulation for concrete block: which way is best?

Ricardo Obsolete's picture

There has been a lot of discussion about insulating block walls in the past, but it seems that most has focused on exterior insulation...

I have clients who have two older commercial block buildings. Both were gutted.  They had one finished out and the guys did metal studs with fiberglass batts, vapor barrier and then drywall.  They now have had problems with moisture-  literally running out under the baseboards. It has been a really hot and humid summer, and I think there are some exterior cracks that are letting hot wet air in behind the barrier...

Anyway, I'm slated to do the interior of the other one. We are in the midwest, so we get 100º summers and -20º winters. They don't want to do stucco on the outside, so I'm trying to decide the best course for insulating the interior. I've seen it done a lot of different ways- any thoughts on the best, most efficient systems would be much appreciated....

Well, if the block wall seems (post #205034, reply #1 of 6)

Well, if the block wall seems to have lots of cracks that let air through it would seem that, aside from caulking them, the best approach would be to line the inside with house wrap.  One way or another you need to keep the air out.

But it may be that the failures of the first building are simply due to inattention to detail in air sealing, or, perhaps, rain working through a poorly-painted wall.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

You are right about that, (post #205034, reply #2 of 6)

You are right about that, Dan.  We are going over it inside and out, grinding out cracks and re-grouting, calulking and the whole thing will be repainted on the outside- and it's getting a new roof.  I'm pretty confident we can get it tight.  After that, though, I wonder about going rigid foam and furring, full stud wall with batts, furring with spray foam, etc. I guess there is more than one "right" way,  but I'm guessing some may be better than others.

heating or cooling climate? (post #205034, reply #3 of 6)

If you are in a primary cooling climate moistur will migrate to the cold sid of the wall. What ahppened with the first job where foam board,f'/g insulation and metal stud were used  was not the cause of the condensation. The interio vb  was. It trapped the moisture in the wall and it codensed on the back side of the poly and the metal studs.

Eliminate the interior vp and let the wall dry to the inside conditioned space.

While it could be condensation............ (post #205034, reply #4 of 6)

I'm make very sure it wasn't rain or drain water coming in from the outside b/4 I buttoned up the interior.

Condensation in volume might run out from under baseboard, but that would be some serious volume.

Is this occuring on the "weather" walls or all exterior walls?

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It's happening on 2 exterior (post #205034, reply #5 of 6)

It's happening on 2 exterior walls- the building has a new roof and it looks tight.  The building does have cracks, as I said before, and needs paint. The water on the floor was showing up right after the AC was turned on, during a long hot, humid dry spell, which lead me to the condensation theory.


The building I will be working on will have a tighter envelope, with cracks addressed, fresh paint, etc. My question is about the best system to avoid similar issues, and get the best insulation job. I don't think there should be a vapor barrier between the fiberglass batt and the drywall, but I'm debating about doing gluing up 3/4" rigid, then putting up furring strips and filling in between with...?

 Readers should note that (post #205034, reply #6 of 6)

 Readers should note that this summer has been unusually hot and humid in the Upper Midwest, probably like the 95th percentile in that regard.  Not sure exactly where in the Midwest this is, but generally the bigger problem is winter heating, as temps can sit near zero F for days on end.  It's not a "cooling climate", generally speaking -- usually just a few days when the AC is seriously needed.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville