Bad sealing possibly insufficient?

Hello,

At our neighbors’ house, which they built in 2016 with the same builder as we did (building year 2017), water damage has occurred due to insufficient waterproofing in the bathroom. The defective waterproofing (no waterproofing under the walk-in shower, not high enough...) was confirmed by an appropriate expert, and the bathroom had to be redone by the builder.

Since we built with the same builder and had the same tiler, we suspect that the waterproofing in our two bathrooms with walk-in showers might be similar, meaning only inadequate or not present at all. We communicated our concerns and requested an inspection but were, of course, rejected. The explanation was that the new DIN 18534 would not yet apply to our house?! The bathrooms were completed in September 2017. Regardless, I would assume that there were waterproofing regulations before that, which might also not have been observed.

My questions: What should have been done to ensure proper waterproofing according to the standards at that time? Could this be identified without tearing everything out? Or should the new DIN have already been considered, even though we were already in the middle of construction? How should we proceed best here? Should we commission an expert directly? Or a lawyer?

I hope the information is sufficient for now and that someone has a good idea. I am quite at a loss but do not want to face damage later that could have been avoided (at the builder’s expense).

Best regards

You describe a difficult but everyday situation -> proof! Your neighbor has obviously sustained a demonstrable damage. Your suspicion: It is the same with me. The judge would say: They have learned from the damage. As long as you do not have sufficient suspicion of a defect, the presumption of innocence applies. You could send your contractor a notice of concern stating that your shower is also faulty. He will reject it. A structural proof is not justified. Just raise concerns and refer to them if it occurs!