Another approach is to simulate the stress skin panel with site-assembled sheet goods and rigid foam. Layer at least 4 inches of extruded polystyrene foam on to the roof deck, then top it off with a layer of 1/2-inch plywood. The biggest challenge with either of these approaches is finishing the thickened eaves area. But that’s nothing compared to the hassle of covering an interior ceiling with insulation.
insulation product generically called stress skin panels. Plug this phrase into any search engine and you’ll find suppliers. Stress skin panels are factory-made insulating sandwiches of plywood or waferboard bonded to a 4, 6 or 8-inch thick layer of rigid foam. Order the panels to fit your roof, then hoist them up top and fasten them to rafters with long, 1/4-inch diameter bolts.