As a contractor I have to say, that insulating and exterior envelope processes must have the least amount of margin for error. And when you do screw up the costs are expensive. I'm thinking about wraping windows for siding or insulating vaulted ceilings. I'm researching cathedral ceiling systems to retro fit existing homes. Lot's of these older homes have minimal insulation and poor ventilation. I'm looking at the insulated panel system. This would consist of a layer of EPS then a sheet of OSB glued on top. The problem with this system is there is no venting. This appears to be a very contentious issue here and with engineers. In fact some shingle companies won't even warranty a roof that is not vented, ie, a hot roof. So, that leaves me with strapping the EPS then sheathing. I don't even want to think about all the build out on this one. I know there is the SIP option but is that the only one?