Shop insulating advice

CFD244 said
Your soffit ventilation would be under the overhang of your roof (it has small holes in it to allow air in). Some metal roofs have a ridge vent along the total length of the peak and does a similar job as your gable vents. Air in through the soffit and air out through the ridge and/or gable vent.

So basically, you would insulate the walls and the ceiling with Roxul or pink. Then you'd cover all of that with 6 mil plastic to give you the vapour barrier that you would need. Then you would board it with drywall, steel siding, or whatever you want. That would give you an envelope that is sealed thermally with adequate vapour barrier to eliminate condensation on the cold outside walls and attic should there be minute breaks in your insulation.

The attic remains dry, cold and ventilated.

This kind of sounds like what I have been doing, I wasn’t planning on adding another layer of plastic before the OSB but I guess I could do that as well, then I would have 2 vapor barriers.

Ok so maybe I have been foaming in the soffit ventilation along the bottom of the roof where it meets the walls and travels up the roof peak. That is what lets in most of the cold air all day long.