Closed-cell spray foam in new commercial construction
Hi. I would appreciate some input on the wall and roof assembly of a new commercial building in the Buffalo, NY area (climate zone 5). The building is a simple 24'x40' box with 10/12 gable roof.
Code requires R-38 for the roof and R-13 (wall cavity) plus R-3.8 continuous for the wall.
Wall: 2x6 wood studs @ 24" o.c. with 5/8" type X GWB each side (1 hour fire rating due to location on lot). Weather barrier and exterior siding (not defined yet). We were thinking of foaming the wall cavities with closed cell foam and applying an additional 1" of EPS at the inside to the studs to suffice the continuous insulation requirement. The idea with the closed-cell foam would be that it works as a vapor barrier to the inside and prevents moist air from travelling through the wall and condensating at the sheathing. There would be ca. 3" deep air pockets between the studs as we would not need to foam the whole cavity depth.
If we were to have batt insulation between the studs (to cut down on cost) would we still position our EPS at the inside as vapor barrier? Or would we put it at the exterior to keep our sheathing warm? It seems that you would penetrate the EPS in both cases with fasteners for the GWB respectively the siding.
Roof: 2x10 wood rafters @ 24" o.c., 5/8" GWB @ inside and 1/2" plywood at exterior, underlayment and asphalt shingles. Closed cell foam between rafters to achieve R-38.
I read the threads about exterior insulation and cold plywood and was wondering if this would be an approach that makes sense.
Posted Nov 5, 2012 4:14 PM ET
Edited Nov 6, 2012 4:22 PM ET
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