Redundancy of Vapor Retarder and Latex-Painted Plastered Blueboard for Vapor Retarder
Climate zone 6.
My wall stackup from the exterior is 1″ hemlock siding, 1″ airspace, housewrap, 2 1/2″ xps, 5″ studwall insulated with r23 roxul.
I understand that the 2 1/2″ xps is marginal for my climate zone and detailing the vapor retarder will be essential to performance.
I’ll be installing blueboard which will be plastered, primed, and painted with latex paint.
Would it be necessary or even just good insurance to install a vapor retarder prior to the blueboard, or will it be an unnecessary redundancy if the blueboard is detailed well?
For that matter, are there any issues with two layers of vapor retarder?
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