Can you mix and match vented and unvented roofs?
I am looking to build using a hip roof for the majority of the house (its a 50′ square in essence), but in the rear corner is a great room with a vaulted ceiling (to be cliche I guess) so it will be gabled. Where the vault meets the hip will be a valley and I think it will be next to impossible to vent. So I would like to have it designed unvented (maybe with 5″ exterior foam, dense packed joists). But the rest of the roof could likely be vented well (or as ok as a hip can be vented).
Can these two intersect ok? Should I run the exterior foam underneath the valley and down to the ceiling plane (since the attic temp will likely be close to exterior temp in the winter) to keep the vaulted sheathing warm? I was wondering if they could frame and insulate the cathedral before framing up the rest of the roof to make it easier (or would this be harder)?
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