I’ve acquired a clear span steel frame building that had an R19 6″ roof insulation included with the package deal. It is faced insulation with wmp-vr (class 4 permiability). The normal building practice is to lay it out on the purlins and screw the metal sheets on top.

The building is going to be built in northern zone 5. It is a repair shop that will be heated with radiant floor heat. There are no code requirements with the building. Building is 13000 sq ft and will have at most have 3-4 people working in it. Biggest moisture contributor would be occasional snow melting off equipment in the winter.

I would like to incorporate spray foam in the insulation detail to help seal the building. Local accepted practice for foam only is a couple inches of closed cell or 4-5″ of open cell foam. A steel liner panel will be installed below the roof.

I would also like to utilize the existing insulation as it doesn’t have a lot of resale value.

Option 1. Easiest way is probably to spray the roof panels direct and cut and stuff the fiberglass to fit between the purlins below. The purlins space is 8″, fiberglass is 6″. This however does not give me a thermal break.

Option 2. Install liner panel first and spray foam on it from above. Roll out fiberglass over purlins. This gives a thermal break on the purlins, but would result in some air gaps next to them. I could also cut the fiberglass to fit between the purlins, would fix the air gaps, but loose the thermal break. Would the facing cause any issues?

Anybody have any creative ideas?