HI.
My home was built in 1952 has a brick veneer with a 1″ space between the back of the brick and the Celotex (fiberboard) sheathing, then 2 x 4 studs.

I am renovating one of the rooms of the house (single story) and one side of that room is an exterior wall (with a window in it) with the aforementioned brick veneer. I am removing the old badly deteriorated disgusting fiberglass batts and replacing them with Rockwool insulation (does not come with a paper facing). I’m in climate Zone 4, southeast PA.

I’ve read the article in the Green Building Advisor website about “When Sunshine drives water vapor into the interior”, and still am at a loss as to whether I should use a smart vapor retarder (like Certainteed Membrain or Pro Clima Intello) or not. By the way, why is it so hard to buy that Membrain stuff, can’t find it readily anywhere.

Rockwool literature states that in climate Zone 4 I don’t need a vapor retarder but I should go by local code requirements.

I just called my local building inspector to ask if I need a vapor retarder. After explaining about what R value I should use, he said flat out , that yes I need a vapor “barrier” (his words), then went on to explain that it could be a “plastic” (didn’t qualify it) sheet or Kraft paper and it should be toward the warm side of the house. He clearly doesn’t realize that the “Kraft” paper on fiberglass batts isn’t just paper but a specially made paper with an asphalt like layer to it that has a purpose. He clearly doesn’t have a clue about the issues of sun driven vapor drive and brick walls and celotex etc as explained on the Green Building Advisor (also discussed by Joe Lstiburek at his Building Science website).

By the way on that side of the house which faces east to southeast, I have a deep overhangs about 14 to 16 inches or so.

It has been in the 40’s here and when I removed the insulation (this past weekend) tucked above the window it was  wet but not the insulation in the walls, only above the window. To which I am air sealing the window like mad.

So given my situation with the brick veneer, celotex and Rockwool…should I use a vapor retarder like Certainteed Membrain, or ProClima Intello Plus or their DB+ vapor retarders? Thanks all.