2018 I got quotes around $12,000 for 3 or 4" (don't recall exactly which it was) of spray foam in 5500 sq ft of shop ceiling. Spent the last few weeks getting the same thing quoted for $27,000 for 3" or $33,000 for 4". The spray foam guys want to do 2" for $19k, but I don't think R14 is going to cut it. I plan to heat this area to about 60-65 degrees all winter with a couple heat pumps. I can't swallow that price so I'm pricing out DIYing it and coming in around $8500 for alternate materials.
My shop walls are R21 metal insulated panels. They are air tight, no thermal bridging. The building base structure is structural steel, but I built the roof deck with 2x6 joists spanning 10' on 24" centers topped with 3/4" plywood.
My big question is, would it be better to use R19 batt insulation between the joists with 2" polyiso foam with edges sealed attached to the bottom of the 2x6 joists, or to just use 4"+ polyiso foam attached to the joist bottoms and leave the area between the joists as a dead air void?
I'm going to attach steel siding with an air gap to cover the rigid foam to finish the ceiling.
Thoughts?
My shop walls are R21 metal insulated panels. They are air tight, no thermal bridging. The building base structure is structural steel, but I built the roof deck with 2x6 joists spanning 10' on 24" centers topped with 3/4" plywood.
My big question is, would it be better to use R19 batt insulation between the joists with 2" polyiso foam with edges sealed attached to the bottom of the 2x6 joists, or to just use 4"+ polyiso foam attached to the joist bottoms and leave the area between the joists as a dead air void?
I'm going to attach steel siding with an air gap to cover the rigid foam to finish the ceiling.
Thoughts?