Batt and Flash (inside out)
After meeting with insulation contractors the last few days, I received the Feb/Mar 2011 FHB with the “Flash and Batt” article. Timely!! But the dew point concerns are sobering… So how about reversing the assembly, where the project details permit?
I am gutting a 1930 balloon framed house, 1400 SF in Rhode Island (zone 5A I think, though there seem to be a number of climate zone mapping schemes…)
Considering spray foam insulation in the walls, 2×4 plus 1″ furring, for a tight seal, full thermal break inside the studs, about R-15. Thicker on the north side.
The attic will be unheated for now, with plans to expand, insulate, and finish it as a 3-season room in “phase II”. Basement is unheated shop space. So I am thinking, how about “Batt and Flash” for basement ceiling and attic floor? 1″ foam against the warm surface, to seal the assembly, with thick fiberglass batt insulation in the cavity. Would this address the vapor issue? Any downside, or detailing to consider?
Also, spraying the wide-open 2×4 bays full of foam, is firestop required between floors? Or does the foam serve that purpose?
GBA Detail Library
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