Insulating a hot porch roof
We’re going to be converting a garage into a large unconditioned screened porch and a couple of conditioned rooms in Climate Zone 3A. Of course, we’ll want to air seal carefully between conditioned and unconditioned space. We plan to use a moderately reflective (~50%) and highly emissive coated metal roof. We’ll also likely use a bead board ceiling in the porch area, atttached to a scissor-truss system.
But the questions: Are there likely to be any significant comfort benefits for the porch to using rigid panel insulation (in the range of r5 to r10) on top of the roof deck? I assume that insulating just above the ceiling would be less useful than insulating between roof deck and metal roof. Does an air space between roof deck and metal roof provide any additional benefits?
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