air space with radiant barrier

lawson roberts
I am replacing asphalt single with metal vertical panel. ( all shingles will be removed) I have been unable to locate a design to incorporate an air gap of 1 3/4 inches (using 2x4 as purlins) and a radiant barrier on top of the plywood decking massive amounts of air would feed from the fascia and exit through ridge vents. I also want the 24 gauge to take 100mph winds and be attached with clips so the panel can expand and contract easily. I believe this would keep my attic at outside air temperature. It seems simple, but the local contactors are at a loss when it comes to addressing air flow and radiant barriers. any suggestions ?
Eric Novotny
An informed customer is the Best Customer!
Lawson, Sounds like it is pretty well designed if you ask me. Is the attic still vented or is it conditioned? If the latter, you may want to incorporate some rigid foam into that roof assembly equation as well.
lawson roberts
Thank you for confirming the design. The attic is still well vented. In fact, I have kept the metal roof ventilation isolated from the attic ventilation. I did so because I feared the air frow from the mental roof would be so good it would suck the cold air out of the living space. I do find it sad that the the metal roofing contractor are failing to package the 2x4 + radiant barrier+ ridge vent+facia vent as ideal for climates that run the AC all year long. You are right on the money about ridged foam, but my guess is, the air flow of 1 3/4 inches with radiant barrier will be better than the foam with a smaller air gap. I have attached a PDF that shows were some local folks are close to getting the air flow, but block the airflow in a large section. Again, thanks for the feedback.

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