How to best finance €100,000 for house construction?

I also no longer see KFW as really worthwhile. For us about three quarters of a year ago it still paid off well, today I would leave it. You should also check some threads here regarding house prices and ancillary construction costs, your budget might be a bit tight.

I would contact the house bank and an intermediary

60,000 equity and 100,000 loan. Do I understand correctly that you want to build a house for 160,000?

Yes, but ancillary costs and house connection costs should not be financed...

What will that be then? 80sqm? Better to buy an apartment then

Yes, but additional costs and house connection fees should not be financed...

From which pot are the additional costs paid?
I don't really see where you want to build at the moment, since I use TT, but somewhere 25-40,000 have to come from.
The house for 160,000 works as a cheap build, but I wonder, what's the point?
Desperately wanting your own four walls, then of course with 2 children's rooms if they visit on weekends, but minimal standard and without outdoor facilities (terrace, lawn, hedge).
In 2 years, when a move might be due, you'll meet your second dream woman, for whom moving to another city is worthwhile.

And then?

Regards, Yvonne

First of all, thanks to everyone who wrote to me about financing. It’s very kind of you to think about my future, but I already built in 2000 and work at the utility company. Because of that, I can estimate well or have additionally inquired how high house connection costs and incidental expenses are for me. The standard is not that low at all

And the arrogant attitude of Steffen80 speaks for HIM