I am contemplating making my attic space part of the condition space of the home. I would like to add 12″ of ComfortBoard outside the existing roof and applying a new metal roof . My first inclination is to put a peel and stick membrane on the existing roof and fasten 1/2″ plywood sheathing on top of the ComfortBoard with long screws as a substrate for the new metal roof. What kind of material should go between the new metal roof and the sheathing? And what kind of provisions (if any) do I need to make to prevent the ComfortBoard from sliding on the roof (7/12 pitch)?