We are not making progress in financing

And what the interest rate will look like in 10 years, pffff no idea. Not even in which currency we will pay it then.
Look back 10 years and think about everything that has changed :D

Are you building a Kfw 70 house would be the first question. If yes, with a granny flat?

Regarding Kfw: 2.65% is the home ownership program. BUT if you build, for example, a Kfw70 house, there is the energy efficiency program at 1.41%. If not, that option is eliminated.

Regarding the building savings contract: I simply see a high risk for you in the annual approx. 8,000 EUR lump sum payment into the building savings contract. If that doesn’t work, the building savings contract will not be eligible for allocation after 10 years and you will be stuck with the full 177,000 EUR at interest rate risk.

This is always difficult to assess from a distance, but I could imagine that you would be better off with, for example, a building savings contract for 50% of the amount (e.g. 80,000 EUR building savings sum). If you really have the 8,000 EUR left over each year, put 4,000 EUR into the building savings contract and 4,000 EUR as a special repayment on the loan. That gives you a much greater savings effect!

So our house will be an 85-efficiency house. That is why the 1.41% would no longer apply.

Regarding Kfw: 2.65% is the homeownership program. BUT if you build, for example, a KfW70 house, there is the energy efficiency program at 1.41%. If not, that does not apply. Regarding the building savings contract: I simply see a high risk for you in the annual approx. 8,000 EUR one-time payment into the building savings contract. If that does not work, the building savings contract will not be ready for allocation after 10 years and you will be left with the full 177,000 EUR at interest rate risk. This is always difficult to assess from a distance, but I could imagine that you would be better off with, for example, a building savings contract covering 50% of the amount (e.g., 80,000 EUR building savings sum). If you really have 8,000 EUR left every year, then 4,000 EUR go into the building savings contract and 4,000 EUR as a special repayment on the loan. That gives you a much greater savings effect!

I see it like Nilo. Securing part with a building savings contract makes sense given the current interest rates. Anyone who believes in falling interest rates over the next 10 years should tell me where they could possibly fall next! (Negative interest

If they are really calculating with 8T€ special repayments here, then I don’t know what interest rate risk there is to hedge. With an 800€ monthly payment and an 8000€ special repayment, after 10 years there is still a 58T€ outstanding balance left. The interest rate can rise above 8.5% from the 11th year onwards without nominally paying more interest than in the 1st year.