Insulating walls with no sheathing
My 1899 – 2 story house has T&G exterior siding (5/4” x 8” novelty pine) nailed directly to studs (no sheathing). And no ability to drain – no weep holes. Most important is the dimensions of the studs – they used 3”x3” (actual measured dimensions).
Reading articles on how to insulate this type of wall I have come up with the following plan
· Create a ¾” air space using nailing sticks in the corners of each stud bay, tacked to the exterior up against the siding.
· Apply 2” polyisocyanurate into each bay R-12. Using adhesive to attach it to the nailing sticks. The adhesive would be Dow INSTA STIK™ Quik Set Commercial Roofing Adhesive
· Using same adhesive attach 1” polyisocyanurate (4×8 sheets) across the entire wall to create a thermal break and add another R-6.
It seems R-18 is the best I can achieve with a stud cavity that is only 3” deep and very roughly 24” on center.
Two articles that where most helpful
1. Insulating walls in an old house with no sheathing
2. All about rainscreens
· Does the Polyiso end up functioning as an exterior air barrier and a substitute for the missing WRB?
· Are the lack of weep holes a serious problem, we get about 48” of rain and 47” of snow a year in Zone 5A, New York.
· With the adhesive used do I still need to spray foam the perimeter of Polyiso. I will probably have a 3/8” gap around the perimeter.
· In article 1 above it mentions “this type of wall is designed to dry to the interior, so you don’t want to install any polyethylene on the interior side of the wall.” Polyiso has a vapor barrier; is that a problem? If not, can I use multiple layers of Polyiso in this fashion?
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