Polyisocyanurate foam retrofit and rainscreen
I have a question about a job I am starting in Amherst, MA. and I would like to hear others chime in about it. This is a whole house exterior renovation (built in 1982) The owner’s want to insulate and install new windows and siding.
Existing wall from inside to outside: 1/2″ drywall, 1″ polyiso., 2×6’s 16″ oc w/ fiberglass batt insul, 1/2″ asphalt coated ‘Beaverboard’ sheathing(OSB on corners), Tyvek ( which has deterriorated) and 1x cedar vertical siding.
I’ll be removing the siding and Tyvek and add 2″ polyiso. board (not taped), 7/16″ Zip wall taped, Homeslicker rain screen and red cedar shingle siding. (Note the cedar shingles requiring a good nailing base)
I’ve done a lot of research and realize that it’s not a good idea to add another vapor barrier on the outside of the wall cavity, but the owners are set on adding exterior insulation. I’m thinking of adding another vent screen under the 2″ polyiso? or switch to 2″ XPS ( a little more vapor permeable, but vapor would still have to pass through the taped Zip wall) or just go with the original plan and not worry about it. 😉
Any other ideas/feedback?