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Retrofit spray foam on the bands of a brick house

Mark Waite | Posted in Energy Efficiency and Durability on

My wife and I have just bought a vacant 1910 foursquare house in Columbus, Ohio. The exterior walls are structural 2-wythe (c 8″ thick) brick walls with a plaster parge, resting on a sandstone foundation. We want to seal the walls with 2 inches of spray polyurethane foam before installing unfaced fiberglass batts in the 2×4 walls that were added by the previous owner on the interior. There is a gap of 2″+ between the masonry wall and the interior framing. Our challenge is getting at the bands at the front and back of the house, where the first of the floor joists rests on top of the foundation wall, parallel with the brick exterior wall , forming a cavity 6″ wide between the foundation wall and the subfloor, and blocking access to the bottom of the brick wall in the basement. The only way to properly open the cavity for foaming is to completely remove the interior wall framing on the first floor and cut back the floor and subfloor. I really want to avoid that if possible, since I am doing all the work myself, except for the foam application. Without removing the interior framing that sits on the floor, I can probably open up a gap of about 1″ to 2″ between floor and wall through which we could fill the cavity with foam (but there’s little or no wiggle room to direct the spray so that it only covers the brick wall). The question is: what kind of foam, if any, would work best for this in terms of not doing any structural damage as it expands in the cavity while providing a reasonable combination of air barrier and vapor permeance? Open-cell foam looks like a recipe for vapor from inside to condense against the outside wall in winter. I worry about closed-cell foam forcing the sides of the cavity – and it’s a lot of space to fill with closed-cell. I have devoured various papers and podcasts by Drs Straube and Lstiburek, but would heartily appreciate any experience or thoughts relevant to this specific situation!

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