Summertime condensation with PERSIST roof – GreenBuildingAdvisor

I am planning to build a PERSIST style roof with only exterior rockwool insulation and an adhered air/vapor barrier like Grace Ice & Water Shield on the sheathing/decking immediately above the conditioned space.

Due to rockwool being vapor open, during my hot and humid summers, I expect that humid exterior air will pass through the insulation, hit the interior decking that is cool from A/C usage, and condense there, resting on the air/vapor barrier. Is it necessary to have that barrier integrated into my wall WRB so that the condensed water can run down the roof and drain away? Or is summertime condensation not a concern in the roof?

Here is my roof structure (from exterior to interior):

– Metal roofing

– Roofing underlayment

– Wood decking

– Vent gap (the roof is vented at the ridge)

– About 8 inches of rockwool insulation

– Air/vapor barrier

– Interior wood decking (exposed to the interior as cathedral ceiling)

I am doing monopoly framing, but my walls (which will have both exterior and cavity insulation) will have the WRB on the outside of the exterior insulation, so out of plane with the roof air/vapor barrier. It would be possible to connect the roof air/vapor barrier with the wall WRB, but it complicates things a little, hence my interest in knowing if that is necessary.