Is a new building financially feasible for us?

(...)
So there are indeed family reasons, but normally you already know those before moving into a semi-detached house next door.
So I suspect the reasons lie with the location or the house itself?

Yes, sure. Just like at the end of the cup match, you already knew before kickoff that the lineup wouldn't work and striker TrifftDasTorNix would miss 2 penalties again. Sure, I get it...

Well... situations can change. The parents might have retired and turned into annoying know-it-alls? Or they separated and one is bitter... or both are bitter because the pension isn't enough...
What has also changed massively and completely unexpectedly in my environment is the political attitude towards certain issues... Corona, Ukraine, refugees, AfD... many families are now divided by meter-deep trenches secured with barbed wire...

I appreciate you, Tolentino, as a competent, level-headed advisor here... don’t stoop to the "should have known better" level of the smartasses here. In interpersonal and especially family dynamics, there is much, much more than one can even begin to guess in this fair-weather and high-earners forum...

Just roughly estimated, what would approximately come your way:
Plot: 80-110k
House: 130sqm x 3000€ = ~400k
Additional costs/outdoor facilities etc.: ~80k
Costs ~550-600k - 150k equity = 400-450k loan
Repayment 3.5%+2% amortization = 1800-2000€ per month + additional costs

Thanks for the breakdown, does it really have to be a 400-450k loan in the end? We don’t have a plot yet. If the whole thing were to start in 2 years, we would have almost 200k equity available.
Wouldn’t a house of 130m² for a price of 2,500 €/m² also be possible? As I said, we would definitely be willing to make compromises and a "standard" equipment without frills would be okay for us.
Also, a Kfw Förderungen 300 would be an option for us.

Now to our reasons, I’ll briefly explain. My parents built the semi-detached house 25 years ago. At first, my grandparents lived in the other half of the semi-detached house, then briefly my sister, and after that I moved in.
Our desire for our own house has nothing to do with the house. The plot is 1,200 m², everyone has their own terrace and enough space for themselves. A few years ago, a new kitchen was installed, all walls were replastered, new floors were laid, recently a new heating system, etc.
It also has nothing to do with my parents. There is no pressure to move out; on the contrary, if it were up to my parents, we should live in the house forever. We have a good relationship, certainly, there are families who might have an even better relationship, go on family vacations together every year, do something together weekly, etc. We see each other regularly and help each other. We handle their paperwork, book vacations for them, order stuff weekly, I do a lot in the garden. In return, my father takes care of all the handiwork for us (I have two left hands). For my parents, of course, it is nice when the grandchildren live next door and they would definitely look after the little one, for example, if my partner goes back to work but daycare has not yet started.

When I moved in here 6 years ago, I always had the thought of having my own house. Living next to the parents forever was not an option. My partner moved in with me 4 years ago. She has no connection to our current place of residence. We like our desired location better. If we were to get a plot in the building area sometime, her parents and friends would be within walking distance, kindergartens, schools, and shopping facilities are within walking distance. The way to the city (my workplace) is significantly shorter and we would have something of our own.

We have an appointment at the bank next week (my partner’s employer) to see what is even possible.

So, above all location. Without a concrete plot, you basically don’t need to go to the bank now. Especially not if you yourselves say you want to tackle it only in 2 years. My suggestion would be to live the next two years as if you already have the higher rate. This way you can on the one hand check if you can manage like that, but also if you want to live like that permanently. And as a nice side effect, the equity will continue to build up. In two years, the conditions for financing can look completely different again. More equity always helps, and prices are currently tentatively stagnating, meaning you’re not saving hopelessly against the market as you were three/four years ago. Feel free to already start looking for other plots in the desired location – I suspect in today’s market situation the new development area will take a while longer – and not only on the portals (which are basically the clearance rack) but actively! If your wife’s parents live there, they should start asking around and you can also find building gaps, abandoned plots, etc. during walks. Your conditions for biding your time are almost perfect. Cheap rent and otherwise no great pressure to move out soon is a situation that not many prospective homeowners have.

Since you are asking now, of course, you can only be given the current state. :) What will happen in two years is something we would probably all like to know (or maybe better not?), but seriously, no one can predict that for you.

Keyword KFW – others probably know better about that, but as far as I know, you would need to achieve efficiency level 40 for that, and that costs a lot of money.

As a note regarding the 3000€ vs. catalog prices. Keep in mind that "turnkey" does not mean that you only have to move in the furniture. And since you are (according to your own statement) not really skilled in craftsmanship, many extra costs will still come up.

Thank you for your feedback. I may have expressed myself poorly. We do not want to address the topic in 2 years, but would like to start soon if we find something and financing works out. The current situation in our desired location is that a development area was completely built up 2-3 years ago. Right next door, the same investor owns the same area. There is also a development plan, which, however, has not been approved due to various issues. Unfortunately, this has been dragging on for several years. Years ago (when interest rates were extremely low), we hoped that the distribution of the plots might start. Since it currently does not seem likely that the distribution of the building plots will take place soon, I just put the 2 years out there. As Tolentino says, we really have a good situation because we pay little rent, have enough space, and can continue to save equity.

Thanks for your feedback. I might have expressed myself wrongly. We don't want to tackle the topic in 2 years, but would like to start soon if we find something and the financing works out. The current situation in our desired location is that a development area was completely built up 2-3 years ago. Right next door, the same investor owns the same area. There is also a development plan, which however has not been approved due to various issues. Unfortunately, this has been dragging on for several years. Years ago (when interest rates were extremely low) we already hoped that the distribution of the plots would possibly start. Since it currently doesn't seem like the distribution of building plots will happen soon, I just threw the 2 years into the room.

As Tolentino says, we really have a good situation because we pay little rent, have enough space, and can continue to save equity.

I can fully understand that and I probably wouldn't want to live in such a family situation for even a year, yet my relationship with my family couldn't be better! Those two things have nothing to do with each other. You want to do your own thing – I can understand that 100%.

In the end, you are certainly also willing to accept financial losses for it, whether it makes "sense" financially or not simply doesn't matter – I totally understand that too. I think it's great if you have found a common path or are planning to.

The saved equity definitely gives you more security than some others here in the forum and also clearly shows that you are willing to save.

In the end, however, your household net income in connection with the child and the planned child still worries me a bit. Your income is okay, but in my opinion not enough for a loan amount of about 450k (which you will definitely need). If you had no children and didn't want any, I would immediately say: Go for it!

In your situation, honestly, I don't know if it will cause you too many sleepless nights, too little vacation in the coming years, and generally too many financial sacrifices.

You have to be able to manage the 2k installment first – I'm speaking from experience here. We have a pretty similar setup to you – but with a few hundred euros more income and a 1% building interest rate, significantly better conditions. Currently, because of the child, we have lowered the installment to 1,500€ and can live very well with it. We don't have to give up anything and are currently only paying off very little principal as our interest rate allows.

In your case, it makes little sense to push the installment down, as the interest will otherwise eat you up. You have to live with that permanently... For me personally, that would definitely be too harsh!

I would leave it... keep saving, maybe a salary increase is still possible?