Can foil-faced polyiso be used on the interior side of a CMU wall in South Florida?
I am building a house in South Florida that has the following Wall Assembly (starting from exterior and working in):
2″ Stone Veneer
8″ CMU Wall
3/4″ Hunter Foil Faced Poly Iso
1 1/4″ Air Gap
A NYC Architect hired by the Owner believes that the home should NOT have 3/4″ Foil Faced Poly-Iso adhered to the inside face of the CMU, but instead should be unfaced Poly Iso claiming that the Foil Face is acting as a Vapor Barrier and therefore the Moisture Drive is coming through the Veneer, Hyrdroban, CMU Wall and then condensing on the exterior face of the Poly Iso.
The point I made is (1) that we do NOT tape the Poly Iso so therefore it cannot be considered a true Vapor Barrier; the Laws of Thermodynamics allow the grains of moisture to move to the driest air and so they will move through to the joints of the Poly Iso and then move to the interior of the home and disappear; (2) the Dew Point is never cold enough on the exterior side of the Poly Iso to be below the Dew Point to allow the moisture to condense on the Poly Iso; (3) even if this were to happen, the Hydroban is sealing up the wall on the outside limiting the vapor drive to next to nothing.
We have done extensive work in Palm Beach Island building VERY expensive homes and this has been the way we have done it… never having any issues… perhaps we have been doing something wrong and just not had an issue.
Does anyone have specific South Florida experience with a CMU Wall using Foil Face Poly Iso? I want to do what is right and have no issue removing all of this and installing unfaced polyiso but I want to hear from someone who is a Building Science type person or can point me to the right person?
Your quickest response is greatly appreciated!
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