Forgot the floor drain. What is the cost of subsequent installation?

After several phone calls and house inspections, the drain was already forgotten by the "shell builder" in the floor slab etc.

Why is it only noticed now?

Here the child has already fallen into the well, but the following advice applies to future builders: - Before(!) signing, seek legal advice. - Consistently supervise the construction, since no one else will do it. - Do not wait until acceptance, but promptly report defects (in writing). - Insist on defect rectification. - At acceptance, absolutely(!) reserve rights regarding known defects.

Oh dear... now surely a user will come and say:
"Take some rolls and a beer to the shell builder, ask him about his and his family's health. Ask how the children are doing at school. Show interest. Then give him 500 more than he actually costs and everything will run smoothly."

The fine difference between MUST and CAN.
The drain in the floor may have its purpose, yet 99.9% of all households prove to you that it also works without.

That is the stupidest "argument" I have ever heard.
Then one could just as well forget to install a controlled residential ventilation system, even though it is listed in the construction specifications.
Why?! Because it works for everyone else without it.

Damn. A forgotten controlled residential ventilation system causes a significant reduction in living value 24/7, whereas a drainage forgotten in the utility room only does so in a very unlikely case of need. So much for the argument...
(or is it supposed to serve other purposes as well?)

In this case, a retrofitting is only possible with partial demolition. So you can't really buy yourself the right here.

Trying to get the maximum financial compensation is the only sensible thing to do in this case. However, I personally think that such a mistake cannot be compensated with just a few hundred euros. If peanuts are supposed to be distributed without legal assistance, I consider consultation with a specialized lawyer(!) at least advisable.

You received something different than agreed. Exchange/retrofitting is impossible. Monetary compensation is the only way. Here, I would definitely make the responsible party pay. This is not a trivial run-of-the-mill mistake.

My argumentation is in my first post. What you are quoting is my response to 11ant.

Pipes also belong to such a floor drain. Anyone who has overlooked it as an addition to the standard construction service description can hardly miss it in all the drawings.

But it has a lousy extra effort-profit ratio. You don’t have to be a great rogue to think that someone might have deliberately forgotten it. And therefore, for pedagogical reasons, I would have the culprit tear up the floor until he is glad that it is only the floor that is being torn up.

It's called increased transportation fare on the tram ;-)