Sealing gap in sill plate
So I recently moved into a new house this summer. After all the dust of moving, painting, etc. has settled (and some leaks sealed during a long, heavy rainy summer), I noticed an area along my sill plate which needs some attention.
The house (at least in this section) appears to have a double sill plate along the top of the basement foundation wall. Right where the steel support beam in the basement meets the foundation wall, there is a longitudinal gap in the bottom sill plate. The top sill plate is continuos, but the bottom one has about a 1 foot break right at the end of the steel support beam (like they couldn’t fit a piece of wood there, so they just left it out…). I can see the bottom support rail for the vinyl siding on the exterior through this gap…
What is the best way to permanently seal this gap? Originally I had planned to pull off that section of siding, installed a piece of pressure treated wood in the gap (with a sill gasket) to seal it, but the AC fuse box and lines are right above the gap so I can’t pull the siding off or even bend it enough out of the way to get a piece of wood in there. My next thought is to slide a piece of flashing under the siding wide enough to bridge the gap, then spray foam the hole from the inside. Does that sound reasonable, and would spray foam wick moisture up from the foundation, so placing a sill gasket would still be warranted? The gap is above grade by about 2 feet, so water intrusion doesn’t seem to be an issue, just a large area of air infiltration that I want to get fixed before finishing the basement next year.
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