I am slowly renovating an old house. In installing a patio door this weekend, I realized that one of the walls is quite far out of plumb. Over the height of the door's 84-1/2" rough opening, the upper end is 2-1/4" further in toward the house than the bottom. This of course causes problems for the door installation, which I've temporarily halted.
The house is a converted barn built in the late 19th century. There is a masonry foundation. On top of that, there is a ribbon joist (some have called it a sill plate, but it's sitting at the same level as floor joists, which some have said makes it a ribbon joist). The floor joists also sit on the masonry foundation, their ends abutting the ribbon joist. But they don't actually touch anymore. The gap is about 2-3". My guess is that they used to touch, and that the ribbon joist has slowly moved away from the floor joists over time. We recently had that section of ribbon joist replaced, since the original wood had rotted. The carpenter replaced it in sections, explaining that the joist held only a compression load (vertical studs pressing straight down) since it wasn't connected to the floor joists anyway. He did toenail the sections of ribbon joist together, but I don't think that he attached the ribbon joist pieces (2'-4' long) to the masonry foundation, so there is little keeping them from migrating.
Since some of you may ask: when this was converted to a house about 60 years ago, they framed a new wall inside. That wall is attached to the exterior wall in places and also to the floor joists below. So, one could argue that the ribbon and floor joists are joined, but my gut says that it's a somewhat tenuous attachment.
So, the questions are:
1) Is something like this abnormal in a building of this age?
2) Is it something to worry about?
3) My guess is that the approach, on an old house, is to arrest the problem rather than trying to correct it, since correction can lead to other problems. Is that right? If so, does it make sense to fit blocks in the space between ribbon joists and the ends of the floor joists, and then lag bolt all the way through from the outside to tie the wall to the floor?