We have a 150-year-old home that has an original-construction bay window whose brick & field stone foundation has sunk away from the exterior wall above (anywhere from 3/8" to 7/8" separation).
First, it's a structural problem because the bay window is just cantilevered off of the house without any actual support underneath. Second, it's a thermal problem because the cold New England air is just blowing through the gap and across the underside of the uninsulated bay window floor, so we have approximately 20 sqft of incredibly cold floor in the winter, and you can really feel what it does to the room.
While I'm an avid DIY'er, this is something I'd prefer to hire out, but for the past few years it's been hard to find people to fix small things like this - especially qualified people. Some have suggested I "just fill it with mortar" which feels wrong because it would contact the untreated wood sills and pose issues with expansion/contraction... right?
Any advice on how to support the sill and insulate/air seal as best as possible? Only the exterior is accessible.