Replies

1. 
   unclemike42 | Oct 31, 2021 06:16am | #1

   Sounds like a good place to have cellulose blown into the wall.

   The sheathing you have installed likely has some insulation value, and no reason to send it to a landfill if it is otherwise intact.

2. 
   12Strong | Oct 31, 2021 02:01pm | #2

   UncleMike42,
   Thank you for the suggestion... I have considered cellulose and spray foam but both have limited availability in my area...

3. 
   unclemike42 | Oct 31, 2021 02:50pm | #3

   Then I would suggest rock wool in the bays

   Do not forget some house wrap to keep those breezes out, and still let moisture escape. (if you do not want to go for one of the OSB products which have a similar coating.)

4. 
   eddo234 | Oct 31, 2021 03:55pm | #4

   I don't have a specific solution for you, but I do have some comments. You're in Climate zone 7, so, very, very cold, Minnesota, the tip of Maine, Wisconsin, North Dakota, the UP, Alaska cold, so the 1st thing I would consider if it was my house, and depending on some other factors I'll mention, is put a lot more insulation in the walls than 3 1/2" of fiberglass or rock wool, R-11 to R-15 is not enough for zone 7. I understand wanting to save the plaster, so if there's room for exterior insulation (with soffit overhang and esthetics, etc.) I would rip off the sheathing, fill the cavities with rock wool, sheath, and add enough exterior rigid insulation over that to prevent condensation on the sheathing (here in Vermont that means, with some exceptions, 2 1/2" of R-5 foam, it's probably more in zone 7). I would research the controversy about Polyiso rigid foam losing its R-value when it's cold if you're thinking of going that route. The issue was that the testing showed its high R-value at 75 degrees, but in cold weather the R value went way down (something to check out before using polyiso). XPS is in the midst of similar controversy about it's real R-value, along with the long-standing greenhouse gas issues with it. EPS foam or maybe rock wool Comfortboard 80 over the sheathing with a rainscreen and siding on that. I also wouldn't worry about an interior vapor barrier, these days it's considered more important to air seal properly. But..... as you said, vapor barrier discussions, and yes, arguments, can get deep, so I'll just say that as long as moisture has a way to get out, it doesn't matter if it's exterior or interior. Another option, but I don't know much about it, and it may be too expensive, is DIY pour foam. It's a slow rise foam that you pour into the top of an existing wall. The slow set/slow rise allows it to fill a wall cavity before setting. The kits on-line cost around $400 for a 200 bf coverage, and $700 for 600BF. For a 3 1/2" thick x 8' high wall cavity the 200BF kit will fill roughly a 7' long wall, the 600BF kit will do a 21' wall, for $700. It's almost R-7 per inch, so R-23-26, you would leave the old sheathing in place, no new sheathing cost, and you wouldn't have to buy exterior insulation if you're happy with R-23-26.