I saw a standing seam galvanized roof installed over skip sheathing. The metal roof was installed about 10 years ago on a 1898 house. Nothing was laid between the roof and the sheathing. I am accustomed to seeing rosin paper used as a moisture/condensation barrier.
Any thoughts?
Condensation should be expected to develop on the undersides of metal roof panels.
An doubled up 36" felt or ice barrier can be recommend at the eave as well. It depends upon the roof in conjunction to the wall assembly.
Most roofing if not all roofing products require an underlay although some manufactures do comment on breathable wood shingle that can be directly applied to plywood.
Love to see the specs on that!
Observation: xx% of the roof deck appeared to have no vapour barrier underlay.
Note: Underlay is required under metal roofing. condensation on the underside of metal roofs is well know and documented.
The roof would be an expensive undertaking to redo just for underlay.
Recommend: Talk to a licensed roofer to see if increased venting or applying more insulation may help.
Yearly/Biyearly roofing inspections.
Note: Routine yearly roof observations and maintenance should be part of any home owners schedule.
Hope that helps.