Leaky bathroom window and mold after 5 years

Well, I would monitor that more closely.. or the landlord (after all, it is in his interest.. he has paid for it and thus has the right to a proper service) and also remove the inside... it wouldn’t matter for just a few tiles. In addition, they can be cleanly separated, so that no damage has to be caused to the rest of the wall.

If the wall has been insulated on the outside, that is already positive.. but then even more incomprehensible that this extremely important detail was apparently not considered.

Unfortunately, I experience such cases repeatedly in daily practice.. a homeowner shows goodwill, has everything renovated... and in the end, the work is botched by the contractors.. or even by accompanying professionals. The latter mostly because they are not on site to supervise or plan properly.

The planning and ultimately execution errors often start with leaving the possibly old exterior window sills, which are known to be a thermal bridge.. If you insulate a facade, those old things are one of the first things to be removed..!

So good luck with the implementation!

Thank you for the explanation, we will probably have to tackle the issue now. I inspected the "spots" on the ceiling last night... we will probably wallpaper. Unfortunately, we skipped the bathroom when moving in because it still looked quite good.. even though we marked a ceiling corner as "dark."

And now we were not in the apartment for 1.5 days and last night I first wiped the windowsill dry (also on the side panels)... there were a good 3 clumps of crumpled toilet paper that had soaked up moisture.

The freshly silicone-sealed joints really paid off.. :(
And in the joints of the wall tiles, black spots are already appearing...

Well, let's see.

Thanks a lot to you all!

Daniel