Insulating Double Brick Construction, No Rim Joists
I have a 100 year old double brick house near Toronto, Canada (climate zone 5 / 6). The joists are partially embedded (all but 1.5 inches is embedded) and appears to have no rim joists. The only section with a rim joist is the parallel section of the bay windows.
Is it common with old brick homes to have embedded joists with no rim joists? I’m planning to insulate the foundation walls with 3″ of closed-cell spray foam and only 1″ between the joists to reduce the risk of rotting the embedded joist ends.
With no rim joists, how does that impact the basement insulation plan? Rim joists are a common area of air leakage. Is there a different area in my assembly that may be leaking air or does the lack of rim joists eliminate that issue? What should I do with the 1.5″-tall area of unembedded joists? I was planning on adding low expansion spray foam to fill those voids.
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Replies
This is very common. Typically there is a gap between the brick wythe open to the attic and the brick infill between joists is nowhere near airtight. Times this by a couple dozen joists and you get a large leakage area. Limiting this area to 1" SPF is a good compromise to allow for some drying.
Usually the biggest leak though is at window headers and bellow door sills. This might need a bit of creative disassembly and hole drilling to get in there to seal it up properly. Spraying just the surface won't air seal. This is much easier to do if the windows are fully removed for a brick to brick replacement. The new windows should seal against the outer brick wythe and spray foam between the top of the window and the inside of the header. Once this is air sealed, you can coat the headers with a bit of spray foam the same as between the rest of the joists for a bit of R value.
Building Science Corp has a series of reports on moisture issues in load-bearing brick walls. This report addresses the issue of moisture buildup in embedded joists, especially as impacted by interior insulation:
https://www.buildingscience.com/documents/bareports/ba-1307-interior-insulation-mass-masonry-walls/view