[jyl]

My wife is painting the stairwell from first to second floor, and noticed the wall above the landing is bulged out about 1”. I got called to figure out if there’s a problem.

The bulged or unstraight part of the wall is about 5’ from top to bottom. The center of the bulge is at the second floor sill level, where the joists and sill and etc would be, and on the other side of that wall is the bathroom and specifically the toilet. So my wife wonders if we have a water leak that is damaging the wall.

I should mention, I have no idea if this bulge is new or has been here the whole time we’ve lived here. This part of the wall is always covered by the stairwell door, which we leave open. I doing think I’ve ever touched this part of the wall, or looked closely at it, in the last 16 years of living here.

This is what I did to investigate.
1. The wall surface (lath and plaster) feels firm, solid, dry.
2. I drilled a couple of holes into the wall at the center of the bulge, the material in the holes is dry.
3. The structure under the landing, at that wall and directly under the bulged place, happens to be exposed (I had pulled off the ceiling board when installing some ducts) and it’s dry.
4. The toilet drain is not in that wall - the drain stack is in the adjacent wall. The toilet supply line is probably in that wall.

My logic is that for a water leak sufficient to swell or deform or damage the structure of the floor, enough to bulge the floorplate (joists, sill, subfloor) laterally - well, it would be a large amount of water for a long time, if it’s even possible. That much of a leak would be visible somewhere - actively dripping probably. The ceiling below should be dripping. So my conclusion is maybe there was a huge water issue once, or maybe the house is just very not-straight in this spot, or something weird happened between 1911 and 2006, but I don’t think there is anything currently going on.

Agree/disagree? What else should I check?