As I was searching through the various posts related to the use of insulated sheathing on the exterior envelope I have not seen anything for or against the use of exterior insulation in combination with 2# closed cell spray foam (1-2″ thick) on the interior cavity. My first thoughts were combination may allow you to reduce the thickness of the exterior insulation, aleviating some of the window/trim detail concerns and still help you reduce the likelihood of the dew point occuring at the sheathing (both are basically vapor impermeable). My concerns is related to the issues that may occur if the tape at the seams of the exterior insulation fails or water/moisture finds its way somehow between the two insulations and has no way to escape, thus rotting out the structural sheathing sandwiched in between? I think i know the answer is to probably not to use this system because of this concern, but I wanted to throw the question out there to get the thoughts of the community. Thanks in advance for your input.