It is at the stairs to the basement ... the distance between the last step and the floor (tile). It is less than the standard allows. So you don’t step into emptiness, but the floor comes sooner than possibly expected (if you don’t look ).
"... than the standard allows" - so both standard and tolerance are missed? - that is a "significant" defect, about whose legal consequences (prohibition of use?) I would inform myself.
I have difficulty imagining how that could have happened: that on the ground floor they decided on a flatter floor structure than originally planned, but suddenly wanted underfloor heating in the basement? - I would rather expect the opposite case.
But I speculate: they decided on a higher floor structure above ground. In order not to have to change all plans to comply with all planned heights (for example with regard to a required eaves height), they simply reduced the story height of the basement and forgot to reorder the basement stairs. And now they tell the client the fairy tale of the miraculous height reduction.
A thousand sprained feet later, one still regrets the convenience of forgetting the defect for a symbolic compensation.
Just state the different heights. Maybe it can also be averaged out. I would be less happy about a few hundred euros than annoyed about it for the next 30 years. Aside from that, escape routes outside the standard can cause other legal problems. How did that even happen?
At the first step, it is about 10 cm. After that, it is 15 cm. The problem actually arose because the floor construction is about 4 cm too high in the basement. As a result, the staircase no longer fits. The staircase itself was correct, but due to the too high construction, it no longer fits. We have decided to have the staircase replaced.