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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Replies
Bill,
The answer to your question depends on your definition of a "screened porch." Traditionally, a screened porch has no solid walls -- just a few posts with insect screening between the posts. This type of screened porch won't benefit much from ceiling insulation.
But in your case, I imagine that your garage has mostly solid walls, and you will just have a few screened openings -- perhaps at the locations of the old garage doors. In that case, the ceiling insulation might keep things a little cooler, because you won't get as much of a breeze.
Thanks ... should have made clear we'll modify to allow three largely open sides. Will put my efforts elsewhere!