Exterior insulation vs. closed-cell spray foam
My project is a major remodel (replacing foundation, moving walls and stairs) in a 2 story 2300 sq ft house in climate zone 3c, zip code 95060. I just received a building permit, and I start construction on July 1, acting as an owner-builder.
House has 2×4 walls and 2×6 roof rafters, all vaulted ceilings. My design calls for exterior sheet insulation (mineral wool) on the walls and roof deck (1.5″ on walls, 3″ on roof), then cavity insulation in between the studs (dense pack or OCSPF), unvented ceiling. Air/water barrier on sheathing, then furring strips to support wall cladding.
I can meet the same insulation numbers using CCSF between the studs. I’ve gotten a few insulation quotes, and running the numbers, CCSPF is the almost exactly same time+materials cost as installing all the layers of exterior insulation on the walls and roof deck. Plus it will only take a few days, instead of over a week to add all the exterior sheets.
If I use CCSPF, there is no added cost for all the extra detailing, like bucking out the windows and doors. I would still use furring strips upstairs to vent the siding, and I would use a stucco drain wrap downstairs for the same reason. No more structural issues with attaching furring strips through mineral wool, no extra cost for structural screws.
Plus, the house is a clerestory design, and using CCSF on the roof means I get over 3″ back, so the clerestory windows can be that much taller.
The most obvious tradeoff is that CCSPF is not an environmentally friendly product. What else am I missing (off-gassing, etc.). I’d love to get any feedback here.
Also: I had specified Blueskin for the air/water barrier under the mineral wool. If I go to CCSPF, what do you recommend I use, if different?