Hi there, seeking advice for insulating and old house. Small two story house near the beach in CT, climate zone 6, with a 4 foot crawlspace, cape cod/folk style circa 1902.
During some targeted renovation, one thing has lead to another (surprise!) and so now just about every wall and floor is being opened up and strengthened, made plumb, or rebuilt. Now that we have the walls opened up, I would indeed like to insulate them, without harming the house.
Key points:
– The exterior has cedar shingles with Tyvek house wrap underneath (rain screen), over the original sheathing boards
– Insulation material: Mineral Wool
– Original studs are true 4″ and in addition to this, some new studs have been added to straighten/plumb some walls whereby the old studs lean OUT and thus create even more of a gap behind the news studs (in between the stud and the sheathing boards; see drawing)
Based on prior research, I think the mineral wool alleviates concern about trapping moisture in the walls to a large degree. But if I use the 3.5″ insulation (for modern 2×4 stud walls) then there will be a 1/2″-2″ gap in between the insulation and the sheathing boards (again, due to the stud configuration, see drawing). I was first going to intentionally leave this gap as an “air channel” to assist with potential drying, but now I’m not sure if that’s needed and/or if that unnecessarily downgrades the insulation’s effectiveness by not being directly against the sheathing. Any thoughts?
Last, I’m considering adding a vapor retarder (not barrier). My candidates are:
– Aquabar B (material is already on site)
– Smart barrier (Certainteed’s “Membrain”)
– Vapor retarder paint on drywall after installed
– Nothing
Any thoughts on using a vapor barrier as well?
Much Thanks for any input!
Replies
I am currently completing a very similar-sounding project on a 1945 brick veneer house in Pittsburgh. I plumbed my walls in the same manner as well, but didn't worry about the extra air space, if any existed.
The sheathing is an old gypsum product that is fastened poorly or broken in spots, so I didn't count on that as an air barrier. I wanted to keep things simple, so used mineral wool batts and a smart vapor retarder (proclima DB+). I bought the DB+ when I started the project a couple years ago and thought remodeling was less costly, but it is a great product to work with. I ran out at the very end, so subbed in Aquabar B for the last 20'. I can tell you Aquabar is more difficult to work with for an interior vapor retarder. DB+ has a sewn webbing of some kind in it that allows staples to hold much better, and holds up to more abuse. Also, I don't think Aquabar is an air barrier.
I'm not an expert on this subject, but thought I would send my experience. I tried to do a fair amount of research before I started my project, and used what seemed the least risky.
Good luck