Central North Carolina....
I have an upstairs addition added over a sunken carport in the mid 70s that transformed a ranch into a split level. The carport was enclosed later (I think) to make a finished basement that is just barely below grade on the uphill end.
There is no insulation in the roof and no attic space.
The roof deck is 2 layers of 2x6 boards over exposed solid 5"x10" rafters.
The beam rafters are on 4 foot centers. There is no ridge beam. There are no collar ties so the roof has some sway away from the gables, but that doesn't seem to have changed in the 5 years we have been here. Pitch is fairly low, around 4/12. No leaks but shingles are getting old. When you are inside and look up, the ceiling is the roof deck. It is a bit hard to cool in the summertime
We would like to change to metal roofing if we do a tear off, but I am worried that the metal roof seams would make the sway look a lot worse if we don't correct it. I have no idea if sway is always bad or if it HAS to be corrected. It does appear to be stable now. If metal would just compound the problems of insulating a structure with no air spaces we could go with shingles again. We don't want to change the appearance on the inside, but I may be able to talk the wife in to accepting a few collar ties.
The obvious solution to me is to tear off the top layer of 2x6s then add 2" solid foam isulation topped by plywood or ply and nailers for the metal roof.
The second solution is tear off all the 2x6s and use them to just build a new house but we would have a bunch of 2x6s left over that we would heave to deal with
... that is a thick pile of wood up there.