Best approach to renovate vaulted ceiling
I have a 1-story ranch in zone 5, Colorado mountains. The great-room half of the house has a vaulted, drywall ceiling about 11 feet high at the peak. The roof structure has 2×12 rafters filled with FG batts measuring 7 1/2 -in, with cardboard baffles above resting on applied ledgers leaving an air channel below the OSB sheathing. Metal roof, soffit and ridge vents. The batts are loosely fitted. The wind blows a lot and pressurizes the insulation space. Cold air blows out of the few ceiling electrical boxes. I want to air seal the insulation cavity from the vent channels and increase the insulation R from the present 24 up to 48 if possible. I would like advice on the best plan. One approach I am considering would be to strip the roof off, eliminate the baffles and vents, add additional R13 batt, re-sheath and add exterior foam. Another would be to strip the interior drywall, seal the baffles to the rafters (maybe replace them with foam board), refit batts, and then add foam underneath. The latter approach would steal a lot of ceiling height I really don’t want to lose. Advice?
An additional question relating to the metal roof, if I choose the option requiring exterior foam, is the best approach to providing a better attachment for the metal roof panels. Currently they are screwed down to the OSB sheathing, and in tightening the screws I have found that maybe 1/4 or more of the screws had been overtightened or overstressed and stripped out the hole in the sheathing. They have been replaced with oversize screws, but it seems that the OSB is not very robust. The wind blows a lot, and it seems to stress the roof panels. The neighbor had a new roof installed and 2×4 crosswise nailers were added over the new membrane, screwed through into the roof trusses/rafters to provide a much better attachment for the metal panels. It looked good, but leaves the panels unsupported underneath. My thought would be to combine this with adding surface foam. Any downside? Or would using ZIP R panels for the roof foam be as good or better?
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