Interior Board Insulation
Hi all, I am upgrading the exterior walls in a few rooms and am looking for some advice on the best method (having already read this article: https://www.greenbuildingadvisor.com/article/insulating-walls-in-an-old-house-with-no-sheathing)
I have a 1955 stucco home in zone 3, stucco over building paper against the studs, rock lath already removed inside. My footing is about 10” above the slab. Because I am in a mild climate my plan is to use 1” polyiso, foil to exterior, over 3/4” strips against the building paper to create the rain screen and air seal. I’ll tape the board at seams and around the edges of each stud bay. I’ll then net the studs and hand pack dense pack cellulose by weight to get to my 3.5-4 #/cu ft target. Then I’ll shear wall (having already added 5/8” anchors in each bay) with 7/16” struc-1.
Then we’re at the point I need advice: I am thinking it would be nice to add another 1” of foam and 1/2” drywall over that, screwing through to the studs and not really adhering the insulation to the sheeting (maybe some adhesive or a few cap nails to hold it in place, figuring the drywall will pin it to the wall). If I can get unfaced polyiso I might go that way. My questions are: will the polyiso and plywood still allow the assembly to dry to the interior as I understand it needs to? Should I use a different rigid foam? Is there much point in a thermal break on the inside of the stud wall? Should I use furring strips on the struc-1 and fill the spaces with polyiso or is furring unnecessary to support the sheet rock?
Finally my issue is with how I address the transition of my drywall over the footing. It’s the main reason I might consider furring the drywall as those strips can continue to the floor. But the studs are flush to the interior face of the footing so I could try to add a water resistant barrier (like a butyl flashing) between the footing and the struc-1, and just extend the plywood down to the floor. Or is that just asking for water damage to the plywood?
Any help is much appreciated!
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