This is a flat roof with no attic and no venting. The only space between the roof deck and the ceiling is the width of the rafters. What is the proper way of insulating this ceiling.
Fibergalss Batts (rolled batts)
You could have it spray foamed possibly.
Either batts or spray. If fiberglass batts are used no vapor barrier, as the paper vapor barrier is not supposed to be left exposed in the attic.
Anthony, you should ask some local builders, as to the question of vapour barrier and venting. I believe outdoor humidity is higher in Florida and there are unique rules there. In my cold wet climate, a tightly sealed vapour barrier on the warm interior cieling is a must. Wouldn’t build anythng with a flat roof, either. 
John Kogel
www.allsafehome.ca
Is the flat roof foam on top?
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[size=3]http://www.naima.org/pages/resources/library/pdf/BI472.PDF](http://www.naima.org/pages/resources/library/pdf/BI472.PDF)
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Hard to tell, but those look like 2"x6" over a pretty long span also, especially on a flat roof.