Cool roof design for hot climate
Working on design for new build in hot and humid CZ-3 (a few miles from being CZ-2). Considering the following roof (outside to inside layers): Composite shingles, roofing underlayment, LP Tech Shield foil coated OSB (foil side down), a 3/4″ vented air gap between 1×3 furring strips (running up roof pitch), Zip roofing panels, and R-40 open cell spray foam between rafters or trusses above conditioned attic. Will have venting from under eave soffits through the air gap up to ridge vents on a 9:12 pitch roof.
My thinking is the foil radiant barrier will greatly reduce radiant heat to the Zip panel roof sheathing (by over 90%) and the heat conduction off of the upper layers will largely be vented out by convection in the air gap. As attics in this area can get up to 150F in summer I am thinking this would be worthwhile approach to reducing summer heat gain. Also, reducing the roof deck temperature should result in longer life of roofing material (some roofing manufacturer warranties require under roof venting).
Any experience with this approach? Is 3/4″ enough air gap? Problems I might have? Too expensive? Appreciate any comments.
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