Installing Rockwool as exterior insulation
We are wanting to install 1.5″ of exterior rock wool and are in climate zone 3 (San Francisco Bay Area – Marin) with a rain screen but our contractor, not having done this or having anyone in his network who has, is concerned about excessive labor/cost to get flat surface to install siding and to get details around windows. Is there anyone out there that has experience with this and he could talk to?
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If you haven't seen it, GBA has a useful article on the subject here:
The article talks about how the builders were able to get the furring strips to lay flat, and how they actually had an easier time cutting it compared to foam, and how they handled details around the window.
I believe seeing the Rockwool and handling it in person will do much to assuage your contractor's worries.
I'm in the middle of this, same climate zone (Santa Cruz). My 1.5" Rockwool was delivered today. We had no experience with this, and the window details are pretty tough so far; windows are now installed and we haven't finalized everything on the exact window detail. We have Marvin Integrity Wood Ultrex windows with nailing flanges, and installed them as 'innie' over the sheathing/ARB/WRB, and plan on stucco as the cladding, on top of 1x4 furring strips.
We put on Henry Blueskin as the ARB/WRB, and found that installing it vertically was much easier.
I attached a detail that could work, but is a pain. We're doing some hybrid of this (second detail attached).
You'll probably get some more replies here, because I know we have a bunch of members currently using exterior mineral wool insulation, but you can also send me an email and I'll try to hook you up with a builder who has experience with this install. Use this email: [email protected]
Thanks Aedi for the article and Phil for your experience and details. Brian look forward to connecting with a builder, I sent you an email
Good luck in the process you're about to go down. I'm currently building my own house with a very similar construction... I"ll have 2'' of mineral wool with a rainscreen that's made out of 2x4's (some people use smaller or thinner material as furring, but in my area, there's only a small additional price for a 2x4 versus something like a 1x3 and the 2x4 won't be prone to splitting).
As to your builder's comments, his fears are going to be correct in terms of cost. I think this is the best way to build a house, but if I was paying a contractor to do it, I'd really need to think if the additional cost was worth it. There's going to be a lot of additional cost for both labor and material. Rigid mineral wool is prohibitively expensive, at least in my area.