Home location in zone 2A Central Florida (Not on the coast). Having 2,053 SqFt living space w/above ceiling blown in insulation R-30 and an additional 1,027 uninsulated space. Fully vented at the soffet with minimal ridge vent. Soon to install 2 solar powered thermostat controlled 1600cfm roof vents. The wall construction is CMU block w/stucco finish. The roof is 6:12 pitch, Arch shingles over 30lb felt paper and OSB. The ceiling plane is tight.
I desire to reduce the heat load from the attic space by installing PolyIso insulation on outer side of the existing 1/2″OSB deck. This would be accomplised by removing existing shingles. Install new 30 lb felt paper, single ply. Install at parimeter -treated 2×6 blocking on the flat. laying in 1.6″thick 4×8 PolyIso planks R-9.1. Closing this with new 1/2″ decking, properly fastened to truses w/appropriate screws and washers and proper nailing pattern for local building code compliance. Applying new fire retardent paper w/19″ overlap. Finished with new Arch shingles and acessories. This will build a insulated roof deck system. The ceiling and attic space is unaltered. Will there be a moisture entrapment concern between the wood decks? Do you offer any further design modifications or concerns I need to address? Thank You, I look forward to your reply.
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