I firmly assume (based on legal advice and various reports of experience here in the forum) that the real estate transfer tax is also payable if the house and the land are acquired from different parties. Even if there were no preliminary contract, the tax office would assume a direct allocation of the land purchase for the specific house construction. Providing counter-evidence would probably also be difficult, since the building plot was divided into five parts and now all five parties are building with the same [GÜ]. The only way out seems to be if you can conclusively prove that the house was only sought after the land purchase, for example by a planning order to an architect followed by a tender with multiple offers. Of course, it would be best if a different supplier emerged than the neighbor. In my case, this is unrealistic, I simply include the amount in the budget.