Recommendations/experiences with spray foam for existing shop

[WinterDeere]

One other thing I'd research about a vapor barrier between steel roofing and closed cell foam is the possibility of trapping moisture between the vapor barrier and the steel roofing which could potentially destroy your roof... RUST.

A lot of installers like to spray the foam right onto the underside of the roof. My big concern with this was that the foam would follow the exact ridge countour of the existing roof, and make future replacement very difficult, so I fit rigid foam insulation into east joist bay and had them spray against that.

This has two advantages, in that it doesn't block off any existing soffit-to-ridge ventillation which may help keep the underside of the roof dry, but also makes future replacement much easier. It was very easy to fit 2' wide sheets of the stuff between my rafters (24" on-center... or as close as 250 years of settling allows them to remain), and I just pressed the rigid foam insulation onto the purlins, and used a few drywall screws to lightly hold it in place.

 

[RayIN]

I see advertisements for block foam in various sizes all the time. I plan to buy it in bulk and insulate the side-walls, the roof was insulated during construction.
When Westinghouse Electric had the 2 acre building they built here sprayed inside with a fireproof shredded-paper mixture, kinda like paste. It was still intact 60-some years later when the building was demolished.
It didn't look good, but it was effective insulation.

 

[CliffordK]

I'm not sure about soffit vents. If you have an open ceiling, they may not be needed in the traditional fashion.

I've picked out a pair of big industrial fans for the rafter peaks (walls) in the build.

 

[gsganzer]

Thanks everyone, for some good pointers.

When I redid my current shop and turned it into an in-law apartment, I used the reinforced vinyl faced fiberglass roll insulation before I set the new metal roof down. It was really simple to put down. The first roll is 4' wide, so it staggers from the 3' R-panel seams and subsequent rolls are 6' to continue that stagger. You put double sided tape down on the purlins and roll the insulation out, with the vinyl facing the climate controlled space. You can buy the insulation with a 3-6" tape tab on one side, so the vinyl overlaps and makes a perfect vapor barrier, insuring a perfect seal between rolls. You don't pull the insulation taught, you want it to "blouse" slightly, so it increases your R-value.

When you lay the metal on top, it obviously compresses the insulation over the purlins and it's easy to shoot the tek screws.

I wouldn't hesitate to use the roll insulation on any new building. You can buy various thicknesses and also different abrasion ratings on the vinyl vapor barrier, even the color, white or black.