Wall Assembly Sanity Check
Hey, all! Long time reader, first time poster. I’d purchased my first home here about 2 years ago in central Wisconsin (climate zone 6B) and I have found myself with quite the interesting structure. The whole house is made of concrete block and during renovations I’d found there’s zero insulation in the walls. As long as I’m opening up walls to update electrical and repair damaged drywall I thought it best to add some insulation. I make my living managing an engineering laboratory so it’s in my nature to want to do this “optimally” (as in a robust design that will keep my family warm and safe). I’d had a few insulation contractors out and when I pressed them with pointed questions based on what I’d learned here and from BSC, I wasn’t inspired with confidence that they really knew what to do with this type of structure (a few admitted as much). So in the interest of being my own advocate, over the last 2 years I’ve basically made a hobby of digging through this site and reading the articles and whitepapers on BSC (printed copies and went after them with a highlighter even). After all of that, I still lack the confidence to implement my plan without “sanity checking” myself against some of you clearly more knowledgeable folks (every time I think I finally truly understand vapor profiles, I find a new wall assembly diagram that makes me question everything).
At one point I did pay to have a PE in the house to look over some structural items and to help me come up with a plan for insulating the walls. I’m looking to check against his advice as well as, based on conversations with him, I wasn’t entirely convinced he’d been keeping up with latest building science practices.
I’ve attached two pictures here. The first is the design the PE recommended. One thing to note (and not represented in my drawing) is that the masonry block has a lot of variation in how plumb it is. Varying by about +/- 1/4″. For that reason I have concerns about how well I could get the foam board he recommended to stick to the wall. I don’t understand the purpose of the poly sheeting with the ccSPF. I thought ccSPF had such low permeability that poly wouldn’t really add anything?
The second is the design I’d dreamt up. Major difference is forgoing the foam board in place of full ccSPF which would negate the block being so out of plumb (I know, not the “greenest” design, but it seemed it would address the air and vapor leakage characteristics inherent in the concrete block). I’d also thought a fluid applied, vapor permeable, air & water barrier might be a more appropriate WRB. One thing not shown was that I’d also toyed with the idea of flipping the studs “on the flat”, allowing a full 2″ of foam and creating even more distace to prevent thermal bridging.
The wall cavity depth is 3.5″ as that’s where the bucks for door and windows landed. I could get creative with that if needed but I’m really hoping to avoid changing that dimension. Exterior insulation is a no-go as I’ve got maybe 4″ for roof overhangs. A local contractor (who is on the forum actually) had suggested a “chainsaw retrofit” but the roof was replaced a couple years before we bought the house so I’m hesitant to go that route.
To anyone willing to take a look and offer their thoughts, I’d very much appreciate it! We’re going on two years without drywall and paying an absurd amount for heat in the winter. My fiancee has been patient with my pace at solving this problem but I think I have a responsibility to get this done sooner rather than later (I promise she’s not making me type that). Thank you!
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