Minimizing Condensation Risk in Low-Slope Roof Assembly
I’m a little confused on what might be the best approach for minimizing condensation risk within my flat roof assembly. Details:
*zone 6A, Maine
*small addition, ~18×16
*unvented low slope roof, .75/12 pitch, EPDM
*hybrid assembly, with 4.5″ polyiso over the deck (~R28.5, not derated as it’s Thermax on the top layer.). Batts in the rafter cavities.
*3/4″ Advantech roof deck is sealed with Prosoco liquid flashing at seams
From my research it appears that a smart vapor barrier over the roof deck, below the polyiso, and wrapped up the roof edge blocking would be appropriate. Thus any condensation that might occur on the underside of the polyiso or EPDM could dry to the inside.
Is this a good plan or is there a better way? Should I just skip this and tape the bottom layer of the polyiso?
The assembly will include a mechanically attached coverboard- won’t the long screws just make any vapor barrier ineffective anyway? Should I just seal up the inside edges of the roof blocking and diligently install an interior vapor barrier?
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