Finally figured out why my bedroom door wouldn't latch anymore

I went trough nearly the exact same thing with my 1945 bungalow last summer. My back door wouldn't latch unless I literally lifted the handle with both hands, and I noticed the trim was separating about a half-inch from the floorboards. Like you, I crawled under there and found the original cedar posts were rotting right into the dirt.

I ended up using three Tiger Brand jack posts to slowly bring the main beam back up. One thing I learned the hard way: don't try to fix it all in one afternoon. I did about a quarter-turn on the jacks every other day to let the house settle. If you go too fast, you'll start hearing cracks in the plaster walls or even pop a window pane. Even after I got the floor level, I still had to pull the casing off the door and re-shim the whole frame. The house had been slumped for so long that the wood actualy took a set in that skewed position. It’s a relief to get that structural peace of mind, but definitly keep an eye on your plumbing lines while you're jacking things back up so you don't accidentally pull a joint apart.

I had a similar panic with my kitchen door last winter, but my issue wasn't the soil—it was actualy an undersized double-header that couldn't handle the weight of a new granite island we installed. Every time someone stood near the stove, the door would bind at the top corner and I could see a gap forming along the threshold.

I tried the jack post route like you, using a 20-ton bottle jack and some 4x4 lumber, but I actually ended up cracking the plaster in the hallway because I tried to level it all in one afternoon. If you’re using those temporary posts, take it slower than you think you need to. I found that turning the screw only a quarter-turn every few days was the only way to get the door latch to line up without causing more damage elsewhere. I eventually had to sister some 2x10s to the existing joists to get a permanent fix that didn't bounce when we walked through the room.

I'm super new to all this home repair stuff and I'm honestly a bit terrified to even look under my house now. You mentioned having to pull the casing and re-shim the frame even after the floor was level—is that somethig a total novice can do? I always thougth if you fixed the floor, the door woud just go back to normal on its own. How do you even know if the frame has taken a 'set' forever or if it just needs more jacking? I'd have no idea where to even start with shims.

You're spot on about the house taking a set. I've seen frames stay crooked for years after a foundation fix. One thing people usally miss when they're re-shimming after a big lift is checking the hinge screws. When the house shifts that much, it often pulls the screws loose or bends them slightly. I always swap the middle screw on the top hinge for a 3-inch structural screw that bites directly into the king stud. It helps pull the jamb back into alignment and keeps it from sagging again once you've got the floor stabilized.

Glad you found somethig under there, but have you ruled out hinge bind or simple seasonal expansion before you go too far with the jacks? I've seen guys lift thier entire subfloor only to realize the real culprit was a loose top hinge pin or the weatherstripping swelling in the humidity. If the door is moving better allready, it might just be the change in airflow from opening up the crawlspace. Just be careful you aren't 'fixing' a foundation issue that's acutally just a door that needs a longer screw in the jamb.