Are construction costs transferable to small houses?

Yes, our relationship with the parents/in-laws is/was also decent to good, but definitely required a minimum distance. The ability or willingness to coordinate life rhythms and priorities with each other is probably a key to the success of voluntarily living very closely together. That’s exactly what I meant, you were more precise there. Thank you.

The thread has somewhat taken a more technical direction (-;

On the topic of heating in a 40-60sqm house:

Thanks for sharing your experiences & ideas.
- Sustainability would be my preference, even if difficult, hence the wood stove with my own forest
- I find electric heating hard to imagine if you still have 35 years of work ahead and it could well be that you might not be home for a year every few years and have to cover expensive electricity costs through the winter because you don’t have any other automatic heating system. Especially at the beginning of your working life (I have been full-time for 5 years), a lot changes. But maybe my idea of heating with electricity is outdated.
- I also thought that you can have a gas tank in the garden (underground) which I could possibly have filled with biogas by farmer relatives in a few years. A few kilometers drive. That would actually be the optimal solution in terms of sustainability, economy and automation, right? A gas heating system doesn’t take up much space either, is efficient and doesn’t cost that much to install.

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On off-topic: Apartment or house

Living in a city *apartment* is personally only bearable for me as long as I am fit enough to seek sun and nature every day. Work forces me to spend 40 hours at the PC. That only works with physical balance, but nature and sun are among the most important things in life for me. In old age (which is what I am working towards with the house) I want to be able to go into my garden outside my door every day. Then I will miss nothing in life.

Topic multigenerational house:

After 10 years of living alone, I lived for 1.5 years as a test with my parents + a sibling with husband and child in a large former farmhouse.
Experiences:
- if the apartments are not completely separated and you have to share kitchen and bathroom, it doesn’t work well for long, at the latest when someone is ill
- if you separate it cleanly and communicate openly that you only sit or eat together in the garden once a week or every two weeks, it works quite well if everyone gets along well

For me personally, it wasn’t feasible (as much as I love my family) because I work from home and have to concentrate continuously for my job. I can only do that if I can block out the outside world and that isn’t easy if, for example, you share the garden that I use for relaxation during work.

If everything was separated, including the garden, that would be possible. That’s what the people who still live there do :)

You are making life a bit too hard for yourself.

Living in the city *apartment* is only bearable for me personally as long as I am fit enough to seek out sun and nature daily. Work forces me to spend 40 hours at the PC.

I completely understand the need for nature, but we all have to work for our money...

Besides the full-time job and private life, this topic can sometimes temporarily overwhelm you (-;

... And most people sit in front of the PC, 40-60 hours full-time, think about old age, how nice it could be, and look forward to home or owning a house...

Honestly, I always have the fear that despite a good education and a well-paid job (I am my own employer), I might one day become dependent on social welfare due to illness

...Because: before that happens, the cards will be reshuffled. Illnesses don't make you a welfare case overnight.

everything over 45-50sqm is taken away. It would of course be easier if you were two, then you have 90sqm.

I can imagine that many do not think about such a situation

And everyone feels that way - okay, almost everyone. We are only human and dependent. And you are not in an alien position now.

Therefore: go ahead with the gas, with a high water table you probably shouldn’t bury it?!
But then set it up, plant trees around it.

If the illness creeps in, then sell half of the property. So what!

Mathematically, you lose money with 40sqm.
You have to be able to afford all these new modular systems. One has to think that only yuppies can afford such a thing.
Whether besides the coziness effect at 40sqm also the feel-good effect sets in, I doubt.
But you can report back to us and convince me otherwise :)

I just quickly googled - for Hartz IV recipients, apparently up to 90 square meters of living space in a privately owned home are accepted for one person. So it actually wouldn't have to be as small as planned. There are already "affordable" standard bungalows of this size.

I just quickly googled – apparently, up to 90 square meters of living space in a private home for one person is accepted when receiving Hartz IV. So it actually wouldn’t have to be as small as initially thought. There are already "affordable" standard bungalows of this size.

That’s true, I must have misunderstood that. However, the cost of the house has to be lower than that of an apartment in the region. Another reason why I prefer a small house is that I don’t want to pay off a loan for 20 years (of course, that’s up to each individual). So far, as a self-employed person, I haven’t paid anything into a retirement plan in order to first be able to afford a house as a retirement provision. That means I will need several years of loan payments after the house to provide for retirement. (Yes, I’m not the only one there.) Of course, a lot of possessions also come with effort (I had to clear out several houses and outbuildings ;-). I’d also like to avoid that. Therefore, I find cubic shapes with open living spaces interesting; there are fewer interior and exterior walls, etc. Thanks anyway for the hint—90 sqm plus utility room certainly gives one more options.

Does it make a difference to the bank's loan interest rate how much total wealth I have, even if I only contribute part of it as equity?

No one will talk you out of it either, the small house.
But it makes little sense if floated or flying homes are only slightly more expensive than an affordable standard bungalow from a budget provider.
You can also be happy with the standard.