Why hasn't this cathedral ceiling failed?
Climate zone 5, northwest Ohio. Evaluating options for improving a cathedral ceiling in this 1970's house.
What's there now, outside in: asphalt shingles on 5/12 roof, original plywood sheathing, full-depth fiberglass between 2x6 rafters, foil facing on fiberglass, 2" polyiso with that bumpy white facing. The polyiso is in big 4x8 sheets, snugged right up to the rafters and held in place by drop-ceiling-type rails. This gives about R-32 or so. Not exactly bad, but when the blower door test started, you could hear the polyiso squish downwards against its supports. NOT air tight, obviously.
Inspection of the underside of the sheathing shows no evidence of moisture. Nor do any other surfaces, such as the white polyiso facing. The shingle nail penetrations might have been damp once in a while, but there is literally NO trouble up there.
Questions: first of all, why does there seem to be so little condensation issues? Second, what might be a good way to add some insulation and make the assembly airtight? I figure maybe just drywall over battens, with another layer of polyiso or EPS in between the battens. Thanks for any suggestions!
Posted Jul 8, 2014 10:06 AM ET
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