Financing house construction / Land (self-financed) overpriced?

But please don't forget that a large part of the Berlin surrounding area is former GDR territory. There, the houses sometimes had a drastically different quality than in the West.

What do you mean by that?
The house was built in the 1930s, but it is simply too small for a family..

Yes and no, because "this bank" does exactly the same as any other reputable bank. :) Sharing only makes sense if building is also allowed on the remaining piece – including the possibility of development.

Objectively, the property is expensive, because you still have to add the demolition costs, but due to lack of alternatives, it might subjectively be a normal price. You make the decision. :)

How high should the demolition costs be estimated? So far, we have assumed €20,000-30,000?
Even if I add these to the price per sqm (30,000/1500 = €20/sqm extra), I come to a BRW of €313/sqm, which is below the official (€320/sqm) and below the commonly traded prices (€350-400/sqm).
So from the bank’s point of view, it is objectively too expensive, since only half of the property is recognized based on the current BRW?!

I don't understand your problem. It is actually almost always the case that the bank calculates much more cautiously. Be glad that you have enough equity to cover this difference and off you go!

So from the bank's perspective, it is objectively too expensive, since only half of the property is recognized based on the current BRW?!

Exactly. Every appraiser MUST do it that way. Of course, the value of the hinterland can always be disputed – your seller will see the value as high as possible, the bank will not from a sustainable perspective.
It is already the case that the seller does not get the current market price – otherwise, he wouldn’t offer it to you so "cheaply" compared to the standard land value ;)

The discussion about the property value we just had.

I apparently am too stupid for the search function. How do I find it?

It is almost always the case that the bank calculates far more cautiously.

But you only know that once you have experienced this situation more than once – or ask in relevant forums. ;)

What do you mean by that? The house was built in the 1930s but is simply too small for a family..

By that I mean that, contrary to the view of , much there is not declared ready for demolition but is actually and objectively not. With a 1930s construction year, you probably don’t have to discuss that. ;)

What should be estimated as the demolition costs? We have so far assumed €20-30k?

I consider that too little, because demolition is one thing, disposal is another, which varies greatly depending on the region. An acquaintance demolished a former mining house two years ago. It cost a good €40k in total, whereby they did much of it themselves, including sorting the rubble to make disposal cheaper.