Is 3/4″ closed-cell spray foam enough for flash & batt?
I’m building a house north of Pittsburgh, PA in climate zone 6. The house is built with 2×4 walls, 1″ blue dow styrofoam sheathing (r-5), and brick outside that. The house is about 3300 sqft. The standard insulation would be r-13 fiberglass batts (which I guess would give the walls a total of r-18).
I already opted to upgrade to geothermal heating/cooling. I was told that I can also upgrade the insulation to a “flash and batt” system for about $3100. They said they’d use 3/4″ of spray foam (which would be on top of the blue board sheathing).
However, after reading for hours about these systems and spray foam in general, I’m not sure that 3/4″ is enough in this climate. I mainly read that 1.5″-2″ should be the minimum. However, perhaps they’re considering the 3/4″ spray foam plus the r-5 blue board sheathing is “enough”.
Does 3/4″ closed-cell spray foam sound like enough, or is this just asking for mold/vapor problems?
(also, my builder is very well respected in this area)
GBA Detail Library
A collection of one thousand construction details organized by climate and house part