I live in a condo that was created from an old school house. A few months about my new hardwood floor started bowing. At one point I had a hump 3" high, so large that there were gaps between the pieces of wood. I pulled up the wood floor at that location and found the cause was water. There is a bathroom next to it, so I started knocking out the walls and found water everywhere and the smell of mildew I ended up demolishing to the studs. When I would hit the tile with a hammer, the tile set would turn to the consistency of wet sand. It was soaked.
At this point I could find no source of the water. All the plumbing was dry. I put a dehumidifier in and dried out the place.
Then I discovered the water was coming from the next door neighbor. Their bathroom is next to mine. I can see through to them and the pools of water under their shower.
When I get the neighbor's water to stop, I need to know what next. The conversion to condo was not done by norm and tommy. Not one stud is close to vertical.
I am down to plywood on the floor of the bathroom. (That is not level and the sheets do not match.) From my experience with the wood floors, I expect that they are set down on the concrete floor of the old school.
Do I need to pull the plywood up? The "Yes" tells me that after all this water there may be something growing down there. Is this likely? Is there any treatment that I could use to avoid pulling up things?
The "No" tells me, "How would I get things back together. The studs/floor plate are sitting on top of this plywood layer. I could cut around the plate but they would never have the same rigidity.
The attached photographs are of the same location taken at two angles. 0002 is from my bathroom through the studs to the neighbor's showing their shower unit and the accumulation of water underneath. It also shows my first usage of expanding foam to try to block the blast of cold air coming from the basement.
0011 shows the ribbon of water coming in from the other side. The seam in the plywood at the bottom has about a 1/8" step down. I have been using styrene sheet to provide a backing for future insulation.
So, once the water stops, should I pull up this plywood or build on top of it?