2-family house: Border construction adjacent to neighbor's house about 70% more expensive!

For 260 sqm with two residential units (so double bathrooms, etc.) plus an extension for the staircase, nothing about that shocks me at all.

Wood is a different material than stone. Therefore, I would have reservations about adding onto an existing building from the last millennium when it comes to the house height. But it is certainly possible. Perhaps the construction method is also a cost driver for you. I would simply get other offers. You should definitely do that anyway for this "non-standard" project. Basically, there is no objection to adding on. It will probably just be quite a bulky block. If architectural countermeasures are desired, that will cost additional money again. The most cost-effective way is usually to build a standard house because everything there is well rehearsed. The best way to save is to convince your parents of 90m2. This way you save at least 25m2 in total and already quickly 45-50k€. For more, you would need more details.

Ok, thanks first of all for the many replies, you have helped me a lot. It is less about the company, more about our "non-standard" project.

Now of course quite a few things have to be clarified within the family first. If we do not agree there, we will probably have to tell the company that we will not get the plot and thus the signed contract is void. Or we stick with the company and look for another building plot. But I would rather put the whole thing on hold for now and, if necessary, pay the architect fees that have been incurred. (My lesson learned for signing too early) Inform myself better and get several offers for a standard house on a plot where I have more freedom for the house design.

The following companies are known in our area. Which do you consider to be "good"? If the question violates any rules, please ignore it! Massa Haus, Hennig, Streif Haus, Haus, Schlafzimmer Haus, Konzept Haus, Danwood or do you know of any that I should definitely inquire about for an offer?

I would ask an architect (small office) in the town/neighboring town what he needs to build such a house in solid construction . For a simple version, in my opinion, that is too much. Maybe it’s also due to the wood prices, which have risen sharply in the last 3 years.

Is solid construction currently cheaper than wood? Or is it due to the type of construction?

My current plan is to build significantly smaller, so 120 sqm would easily be enough for both of us with plans for children. That would be a great single-family house. If we still want to build a two-family house with a ground floor + attic totaling 120 sqm, the question is how many sqm would still be available on the ground floor? Since the technical room also takes up space there.

I don’t know to what extent this is feasible, but I would spend about 400,000 on a house, either with the existing plot or at another location. Everything should then also be calculated with additional costs and the material price for own work. Does that work?

So you have the dilemma that you have already signed for the house, but you only get the land if you include the parents-in-law in the house? If I had to guess: no money is contributed by the parents-in-law, since they own the land... but there are wishes regarding how it should be downstairs...?