I finally looked under that bottom piece of siding, on the rear corner of my
house which is on a slab. (used to be a carport, they made it a room.) The
sill plate and corner post had old dryed rot and possibly old termite
damage, no water and no active infestation. But the sill plate (bottom of
stud wall) was rotten, etc. So I screwed a 2x6 into the studs after removing
some siding, and jacked up the whole corner of the house, just a little bit.
I cut out the rotten sill and replaced it with PT. Also scabbed some PT onto
the rotten vertical studs which rested on top of this new sill.
When I was done, there was a little bit of crack in the (new) sheetrock
inside, which I attributed to the sheetrock being put in while the back of
the house was lower than it should have been. But slowly, the door which is
around the corner 90° from this back wall, has gone out of square. If I hang
a plumb line off the top rear corner of the door frame, the bottom of it
will be between 1/4 and 1/2" from the bottom corner. There's a gap at the
latch side of the door and I have to lift it to deadbolt it now.
My problem is, I don't know how to figure out: Did the door get installed
after the corner of the house sunk, or did I jack up the corner of the house
higher than it was originally, (abouit 40 years ago), or more importantly;
what the hell do I do now?