Building a house as a temporary solution (for about 10 years) reasonable?

Buying back [Inhalte in eckigen Klammern dürfen nicht übersetzt werden] as a capital investment I consider risky. Because maybe they will become even more expensive, but at some point it will crash. Then they won't be worth what you paid for them today.

Land to buy.... is what it should mean

Strictly speaking, after 10 years we would have already saved €72,000 in current rent alone. So such a "loss" on the sale would naively not represent a loss.

Strictly speaking, this seems to me to be quite a naïve calculation ^^

Since you cannot have paid off €140k in 15 years with a €600 installment, I assume that you want to use a considerable amount of equity. For this equity, you could/can earn interest income which would be lost if it is tied up in the property! At the same time, the €600 installment consists not only of principal repayment but also of an interest portion which, similar to the rent, should also be recorded as a "loss"...

These €72,000 will therefore be significantly reduced..

There are riskier investments. I cannot - like everyone else, as already said - see into the future, but you simply cannot multiply land... ...

In the "savings calculation" of €72,000, I discreetly refrain from commenting, as this thinking is really naive. Interest also needs to be paid.

Thank you very much for your opinions. I would like to add some collected comments and explanations regarding your posts that clarify my situation a bit more.

@Fiddy The interest for our project would amount to almost exactly 13,000 euros. Thanks to the fixed interest rate for the entire period, it is calculable. If selling the house actually turns out to be the better way, we could do that only after the loan period, if the premature sale really proves financially problematic. Fortunately, a major renovation of the grandparents' house is not necessary – that's why it is so attractive for us. My grandparents are constantly working on modernizations. In the last two years, triple-glazed windows, a completely new roof, and six solar collectors with a gas condensing boiler have been added. I would guess these won't be the last improvements made to the house.

@karliseppel I don’t have to pay back 140k to the bank either, but only 80k. (The rest for house, land and other costs is fortunately equity.) The aspect that my grandparents still need the capital of their house for care also crossed my mind. Thanks to a high pension and substantial financial reserves, this shouldn’t be a problem – of course, you can never guarantee that, that’s true. There is indeed a small risk here that I still need to think through for a few nights.

@Musketier A really interesting idea with the disability-friendly bungalow. I haven’t thought about it that way yet. That will be taken as a possible scenario in the brainstorming. :) Thanks!

@Der Da As I already said above: fortunately, we even have significantly more than 80k in equity. That explains the loan term and interest. In fact, for the reasons you mentioned, we initially also considered a condominium. But the apartments here in Braunschweig are by no means affordable with a clear conscience. Here, I would have to pay more than twice as much for a reasonable 4-room apartment without a garden and without a parking space as for our new house with garden and carport (admittedly somewhat outside Braunschweig). At the moment we don’t want to invest that much.

@ypg You hit the nail on the head that bothers me exactly: If only I knew what will actually happen in 10 to 15 years, my decision would be much easier. This is really a lousy situation and that is exactly why we are still so uncertain which is the right way.

@Shism Ok, I admit, the simple-minded assumption is exposed. :) I only wanted to show the tendency that it’s not necessarily about a high return for me, but simply also somewhat to offset our own uncertainty regarding financial matters by relying on tangible assets. If in the end I break even, that would still be fine by me. Of course, I am happy to take more if it happens – obviously. But it would be enough for me without great worries to save on rent in the end and to get back what I invested through a possible sale price or rental income. The saved rent can therefore be calculated into the depreciation of the house – with whatever deductions.

By the way, a big thank you to everyone for giving me such good and serious suggestions and advice. I was already worried that I would only be met with a few meaningless phrases. :)

I’m happy to read more comments. :)

Best regards Sebastian