Hello!
Sorry that I haven't been in touch for a few days, I was on a business trip abroad...
So: The developer was here, measured the moisture and identified the transition from bathroom to hallway as the source pretty clearly. In this respect, he suspected the underfloor heating, even though it seemed strange to him that no pressure was lost.
The next day, a company came for leak detection (sent by the insurance). The suspicion quickly fell on the shower. We have a tiled shower. The tiles are glued onto a subfloor tray, which is sealed against the wall and the screed with sealing tape. Now there is a gap between the drain channel and the tiles (see attachment) that is not sealed. This was suspected as the source of the leak. Indeed, during the inspection the drain was blocked, yet some water "disappeared" from the shower within about half an hour.
The tiler said he would do it that way everywhere and has never had any problems so far. That seems plausible at first because he has worked for our developer for a long time and the developer has a very good reputation (we know many who have built with him).
The leak detection company then performed a pressure test on both cold and hot water (everything tight) and completely ruled out the underfloor heating.
Conclusion:
We don’t know exactly. If it was the shower, the problem has been fixed, but I’m not certain. We currently have no other plausible causes. The insurance pays for the drying and the relaying of the laminate flooring.
There still remains the often mentioned theory of a one-time damage event. But we can definitely exclude this ourselves.
Many thanks for your support,
Uwe
