Best way to insulate a vaulted gambrel roof? – GreenBuildingAdvisor

We are in the planning phase of a project in Conifer, CO (8300’). Building a shop with ICF walls/floor and open span Glue-lam rafters from Starwood rafters. Living space will be on the second level in the vaulted ceiling. Our plan is to live in the shop while we build the house, and eventually use it as a space for guests. 

I’m struggling to find the best, most cost effective way to frame the roof over top of the rafters. We are considering SIPs more than anything but cost is pretty crazy. We have looked at OSB sandwich panels, and the Ray-Core foam panels with integrated 2×8 studs.

Would we be better off framing with purlins, sheathing, and exterior insulation board with offset seams? I’ve considered spray foam but would like to avoid it if possible.

What other insulation methods should we be looking into? The property will be off grid so R value and airtightness are important to maximize efficiency. We want to build it right, but spending too much on the barn will take away from our home budget.

Also, what other issues/mistakes do you see in our early plans?? I’m sure there are plenty.

Thanks!