I am here to get opinions, not be insulted. Before I do something, i like to be informed and have a discussion on how people think or do things so I can do things right. I know i wanted the walls sprayfoamed. That was easy, but I wanted opinions on how to proceed with everything above. We are getting into summer so doing above was not a job that I wanted to rush into uninformed. My question now is if I was to spray under the roof how many inches would one put. I do understand that for my zone it states R30-R68 but that all based on fiberglass and loose fill. does spray have the same requirements being that it is an airseal?
To your first point: grow thicker skin around here because there are guys that have "been there, done that, got the t-shirt" and they dont mess around when they see an issue. Their delivery could be "better" I dont disagree, but their opinion, based on experience, is valid.
To your later point on R-value, I did some research on this when I decided to do spray foam on the underside of the roof on my new build house. The spray foam guys in my new house shot between 6 and 8 inches of open cell on the roof deck. So lets say for argument's sake 6" at an average R value of 3.7(just pulled that from google) per ", so R22.7. I think the spray is thicker in a lot of areas, but ill go with what I believe is min thickness. In my zone(3) attic insulation required is R38. Your Zone 5 is the same for non Group R(residential). If this was a zone 5 residential structure you would need R-49. The energy code doesnt differentiate between WHAT type of insulation, it just states R-values.
So my spray foam at ~R22.7 on the underside of the roof deck doesnt meet the R38 code for attics in my zone. It does meet the requirement of R20 for "entirely above deck" yet it doesnt meet the definition.
I asked the county/city code inspector how this worked and he said, and this is specific to my area only obviously, that they count spray foam on the underside of the roof deck in the same category as "entirely above deck" because the codes are not written with spray foam characteristics in mind. They determined(through what means I dont know) that spray foam under the deck acted the same as something like XPS panels above the deck. MY guess is their reasoning is that with either above deck XPS or below deck spray foam you are keeping the heat from the sun exposure out of the attic space and moving the conditioned envelope up. With on ceiling blown in you are trying to keep heated air that can go 50+ above outside ambient from penetrating your ceiling into your conditioned space.
Anyway, back to the point. Call your county/city inspector and ask the question of what they require for your structure. My guess is the requirements are WAY looser because its a shop, not a residential. They may require no insulation(which is probably the case for a detached barn or garage) and in that case you can do what you want. But that would be my first call(it was in my case) to see what, if anything, they will require.
