How can I seal this space w/ moisture in mind?
I am working on renovating our second floor which includes putting in a master bathroom and gutting and redoing an existing 2nd floor bath. It is a 1952 cape with brick siding on concrete block. The masonry walls are completely uninsulated in most cases. I have taken advice from the GBA site while researching various issues associated with this project and figured this would be a good place to ask about this.
My question arose when looking into an electrically heated floor for both the bathrooms (probably Ditra Heat). These bathrooms are adjacent to each other along the same rear exterior wall of the house, and their floor joists are built directly into the very top of the masonry wall before a wooden dormer starts (which is the exterior facing wall of both rooms). The joists are 2×8’s.
Conventional wisdom is to insulate the floor joists directly under the heat source which I intend to do (I have some older kraft faced R30 that I wanted to repurpose for this). However since the sill of these floor joist cavities are exposed to masonry, it got me thinking whether or not to insulate all the way to the exterior wall as long as most of the floor was exposed (though not all… I’m not tearing up all the subfloor just for this). This in turn got me concerned with creating new condensation problems in general.
I have attached some pics to better illustrate, and these are a bit older. Right now there is Roxul R15 in the 2×4 exterior walls covered with Certainteed Membrain (there is foil-faced styrofoam under the siding so I wanted the walls to breathe, plus I like Roxul better). I have also foamed the obvious gaps and cracks in the masonry to try to air seal as best as possible.
My question is pretty simple. As long as I’m in there, is it worth insulating up this small area of masonry, and if so, what’s the best way which will cause the least problems? I have plenty of Roxul, Membrain, fiberglass, and even some foil-faced polyiso lying around at the ready, so hopefully I’ll be spoiled for choice. Thanks in advance for any advice!
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