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Vapor retarder … gysum board versus blueboard/skim coat

Wooba Goobaa | Posted in General Questions on

Getting ready to close the walls on a zone 5 reno.  Wall assembly (out to in) cedar clapboards, 1/4 air gap, Blueskin WRB, gapped board sheathing, dense pack mineral wool, skim coated blue board, latex paint

It is my understanding that we are not required by code to install a vapor retarder inboard of the mineral wool (wall is vapor open w/ air gap under the siding), that gypsum wallboard/latex paint is fine on the interior.

Question.  Does this calculation change with blueboard/skim coat/latex paint on the interior?  I guess I am asking what is the permeability of blue board/skim coat/latex paint.

Thank you

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  1. Jon R | | #1

    Latex paint has a wide range of reported perm values. Anywhere from 3 to 19.

    In addition to code, make sure that the wall complies with the recommendations in Table 2 A or B here.

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