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Capping the ventilation gap in a retrofit masonry home?

Richard Ugarte | Posted in Green Building Techniques on

Location: Maryland.
As you may recall, I have a masonry house, built 1938, and am looking to retrofit with insulation. It turns out my neighborhood is being considered for historic designation. So I’m considering how to keep the outside brick facade. I think that a historical designation would also prevent me from placing the attic insulation on the roof deck, since it would cause a much taller trim, altering the appearance. So I’m thinking of keeping the insulation on the attic floor (where it currently is). My question is whether I can extend this attic floor insulation to the very edges by spray foaming the ventilation gap at the top, for a fully tight lid. My concern is that this would obviously convert a ventilated brick wall into a non-ventilated brick wall (though with a drainage space). (My home has the typical 1.5″ ventilation gap between the 2-wythe load-bearing walls and the interior plaster walls, that is continuous from vented attic to the basement).

If I do cap the ventilation spaces at the attic, to cut down the massive convective losses, should I worry about my plaster walls becoming wet and moldy during the air-conditioning season? I have read all the articles on GBA and BSC I could find on the solar vapor drive, but they all seem to refer to brick veneer and sheathing – not retrofitting brick with plaster. The south-facing interior walls have never had vinyl wallpaper that I know of, but as part of this is the kitchen, I cannot be completely sure. Would covering the south-facing brick with a face-sealing product be a good or bad idea (I have seen Dr. Lstiburek talk of them favorably, though I can’t locate the citation at present).

Thanks in advance.

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