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Warm-Climate Cathedral Ceiling Assembly- Any issues with these materials/lack of vapor barrier?

BuildingFun | Posted in General Questions on

Does anyone see longevity issues the following material/build choice? Located in San Diego.   

-From inside to outside.   
-Joists are 2×10.
-Primed/painted T&G boards 5/8″ drywall (primed) for fire barrier. AIR SEALED.
-23/32 cdx plywood-AIR SEALED(was free- using as easy nailing surface for T&G)
-R30 Rockwool (7.25″) slightly compressed to 6.75″ to make fit in cavity
-1″ GPS R4.0 unfaced foam board with perm rating of 3.0, fully air sealed. Used to build on-site insulation baffles, with 1.5″ air gap between this baffle and bottom of roof assembly (old tar paper/shingle setup)

This has been a labor intensive setup and I just want to make sure I didn’t overlook any steps before drywalling and starting the finishing process. If my research serves me correctly, there is no need for a vapor barrier given my mild climate (San Diego), meticulously air sealed drywall AND plywood layer, and semi permeable insulation baffles (Perm 3.0).   If anything, it sounds like a vapor barrier could be harmful as my currently assembly can dry both to the inside and outside, if needed.  Correct? I’d rather spend the time/money to do it right the first time but after reading dozens of articles, thats not always a crystal clear path.

Open to ideas/suggestions


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  1. Expert Member


    That sounds like a good roof assembly for where you are. My only question is whether you need the drywall. Our code would accept the T&G or plywood as a compliant ceiling for fire spread.

  2. BuildingFun | | #2

    Ooooh! That would be neat if I could eliminate drywall layer. Will research.


  3. BuildingFun | | #3

    oops. duplicate

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