Unvented cathedral ceiling
I’ve read some of the other threads about this but since they didn’t quite answer the questions I had, I posted this.
I have a ranch house built in the early 60’s here in central Ohio. It has a low pitched, cathedral ceiling with an interesting issue. The overhang has soffit vents that upon inspection enter into the roof cavities, but all the 2×8 cavities are blocked at some point before they reach the peak. So there is no air circulation under the roof after a point (maybe 10-12 feet from vent). This has caused some issues in areas closer to the peak with summer condensation at times and I’ve found remnants of moisture when I’ve remodeled in the past. And the way the roof is built there are two major beams (2 joined 2x10s) that run parallel to the peak on either side where I would imagine some thermal bridging is taking place due to the old and/or bad insulation.
What would be the best way to insulate a roof like this? I’m about to remodel another room where I’ll be removing ceiling drywall and will have to re-insulate. I’ve read about the “hot roof’ concept and wonder if this would apply here since I have no ventilation. Could I just fill the cavity with fiberglass and not worry about an air space since there is no ventilation anyway? And if I used fiberglass could I use plastic as a vapor barrier? I’ve recently read about vapor retardants that look like plastic but breath a little and wonder if that would be better.
Also, I know in the near future our rubber roof will have to be replaced and probably most of the decking. Could I at that point remove the current insulation and spray in closed foam from above as opposed to the traditional method of doing it from the inside? I’ve never read about doing a retro-insulation job like that.
Thanks for any input.
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