Building with a general contractor - claim for additional costs shortly before the start of construction

Why? There are differences between "fixed price", where quantity changes etc. are not taken into account, and a "flat fixed price", which is truly unchangeable.

I specify my statement. That referred to the last sentence. "A guarantee of not passing on interim price increases is neither connected with nor included in it."

I specify my statement. That referred to the last sentence. "A guarantee of not passing on interim price increases is neither connected with it nor contained therein."

And that is exactly how it is (thank you for your private message with further information on this). The Building Code and VOB may basically address the passing on of price increases (similar to general terms and conditions). However, this alone does not imply that a fixed price has been agreed upon.

It has been noticed that the OP was no longer present here after his opening post, hasn't it?

And that is exactly the case (thank you for your PM with further information on this). The Building Code and VOB may (similar to GTC) basically address the passing on of price increases. However, this alone does not imply that a fixed price has been agreed upon.

If YOU mean a final total fixed price by this, then a lump sum offer should be aimed for. Otherwise, if it is a unit price contract, only the respective unit price is fixed of course.

It was noticed that the OP was no longer present here after his opening post, right?

Yes, of course. Only here in the future maybe someone will show up and then there will be statements to clarify.

And what does it look like when the price for the house is notarized in a purchase contract? One should be quite well protected as a customer regarding price increases, right?