Hi i have a house i'm remodeling and plan on moving the furnace into the attic. There is no basement and at only 600 square feet i don't want it taking up floor space. So to do this I need to insulate the roof deck. Is this doable with rigid foam or do I need it spray foamed. I know spray is better but the cost make me want to check for other options. From what i understand bat insulation isn't an option. I live in climate zone 5. let me know what you think is best or if there is additional info you need for a better answer. Thanks in advance.