New single-family house - realistic estimate of construction costs? Experiences?

Perhaps I expressed myself unclearly. The 3% repayment is what the current costs would amount to. 440,000 means 290,000€ loan, with a 1100€ budget that's precisely 3% repayment. But that is actually not my goal because then I would be paying off for about 27 years. That is why I also mentioned a limit. This results in three options for me: accept it, reduce construction costs, or increase the installment to reach the targeted 4% (1400€). 5% does seem too much for the costs indeed. 1400€ still sounds manageable for me with some minor limitations. When my partner works again, I will no longer have to fully cover her expenses. Corresponding salary increases are to be expected, so a second child should not financially ruin us either. Perhaps it also makes sense to stay at 3% repayment and resolve corresponding situations through special repayments.

It is my equity, I have earned a corresponding job and we are not married. She has no significant assets nor a corresponding salary. Therefore, I am of course the sole name on the land register, since I bear the installments and maintenance costs alone.

And she won’t have your back so you can do your job? Who will look after the children and raise them?

What you can only do alone because you are maximally relieved elsewhere (household, education, social care). Do you really find the equivalent you want to offer appropriate?

Such things are not paid monetarily. If you had to "market-price" buy such a service, the house would be history.

For this reason, the argument about your wife's salary is pointless. She secures a part of your salary through childcare and housework.

I could hardly believe I was writing this, but: Let her co-finance, be on the land register together, whether you HAVE to get married is questionable, it will certainly be easier.

For that, there is more relaxed financing, a better house for 3 children.

That you want to squeeze 5 people into 120 sqm just to finance alone sounds like a bad plan to me.

That you want to squeeze 5 people into 120 sqm just to finance alone sounds to my ears like a bad plan

Certainly true, we are only two, building 150 sqm, and we already think it definitely couldn't have been smaller.

Factual opinion:
If you want to handle the project alone, the bank will not give you the loan (the way you want it)! Why? Because in case of separation, you have to pay child support of 3 times €350. In addition, there will probably be a "settlement" for the woman. Yes, you are not married, but with 3 children you have a marriage-like community, good luck explaining that differently to the judge!

Personal opinion:
Your wife should get away from an egotist like you as quickly as possible xD
Marriage on equal terms ... you better build in the Middle East and put a headscarf on your wife and forbid her from driving ...

Sure, there are only two of us, we are building 150 m2 and we already think it definitely shouldn't have been smaller.

You just have to remember: a house is not an apartment. With a house, I have to include the building services and housekeeping in the given square meters. In an apartment of the same size, there would be no basement or building services within the apartment. Here, I would have still considered 120 sqm as acceptable for 3 children. In a single-family house, no-go.

And since financing for something significantly larger will hardly succeed, there is actually a connection from the off-topic of life philosophy to the topic: It makes no sense this way! Either leave it as is or organize it differently.