For annoying reasons (drawings were wrong, framer didn't catch in time), the roof on an addition we're doing was built lower than it needed to be to line up with the soffits on the existing house. We decided the easiest solution would be to just build up a 6" frame on top of the sheathed roofing so that the new higher roof would line up correctly. The original roof is still in place and has 6" of open cell foam on the underside. The result is that we have a roughly 6" dead space between the foamed, sheathed and papered original roof and the new sheathing. We're putting a metal roof on. Question is, do we need to vent this space? I don't believe there is an ice dam issue since the foam under the original sheathing is an air barrier, correct? Are there other issues that are requiring this area to be vented?