Newly built two-family house with a granny flat

Without land costs?

Correct.

Yes, such prices are easily achievable. We also have a clear 4 at the front of the pure construction costs for our 190 sqm...

We are building a single-family house in Kaarst (near Neuss (near Düsseldorf (near Cologne))) with 127 sqm without a basement for 270,000 EUR including 2 garages and incidental construction costs (plus incidental acquisition costs) and apart from a few electric shutters, a fireplace, a bit more insulation, and a geothermal heat pump with underfloor heating, we have no special extras.

I want to claim that depending on the size, you will easily have a 4 or 5 followed by 5 more digits in the end.

Then I guess the basement will have to go after all. But until now we had one, it won't be easy, you can get used to it. Otherwise the project won't be feasible.

Then the basement will probably have to go after all.

That is reasonable. But even there, with additional construction costs you will probably have almost a 4 at the beginning. A two-family house is all well and good. But what about the additional granny flat? Does it have to be there? Why do you want to have it?

Regarding the real estate transfer tax: No idea what the city told you, maybe you misunderstood it. But the city per se has nothing to do with the RET tax. And the tax office will not waive it, why should it? It has nothing to do with your "old property." Better ask again.

The son, 24 years old, is supposed to move into the basement apartment first, later it will be rented out. I called the city again, it is basically the case with apportionment procedures that no real estate transfer tax has to be paid.