Can an average family afford a single-family house at all?

Good that you know everything. I can also remember a specialist article (it was at an environmental and recycling conference around 2012), where it was forecasted for 2050 that Germany would become a tourism country. Due to the industrial development of Asia and other developing countries, we are no longer competitive and are orienting ourselves towards tourism, for which Germany has a perfect infrastructure. I don’t necessarily believe in that, but it’s not out of the question either. Therefore, I would not want to try to define the demand in 35 years. The journey is the goal and a house is not only "worthwhile" once it is paid off.

And of course, a house often works as retirement provision. How many houses built 30-35 years ago are "junk properties" today? I can’t think of any. Some farms, leftover farms, or post-war buildings with renovation backlog in the sticks are certainly hard to get rid of, but that’s not the plan either. Of course, it doesn’t always work out that the grandparents built cheaply in the city, maintained it with little effort, and the grandchildren can now sell it for exorbitant sums. But the vast majority of buildings do have a decent residual value. Even if the region and prices generally decline, there will always be a market. Of course, those who build in Ottenstein shouldn’t be surprised in the end that it’s hard to sell a house. But those who build about 30 minutes from a larger city and can reach a highway in 20 minutes will always find a buyer. Moreover, very few have an interest in selling the house later. Either it is rented out or the children occupy it. For the nursing home, one should rather get a proper long-term care insurance. In my opinion, a lot of panic is being made about that.

to all the dreamers who believe in the fairy tale "retirement provision single-family house" and preferably still build in the countryside -> On Spiegel today there is an article "When the municipality gives away building land"

yeah yeah well researched:

"The catch of the report was at the same time the mayor's reason for the unusual action: Ottenstein is off the beaten path, it takes 20 minutes to drive to the next district town, almost an hour to the highway – that deters many people. The free building plots are supposed to lure them – and thus help against declining population numbers."

I no longer count that as the metropolitan outskirts. Even in old age, you need good infrastructure, hospital, doctors, care companies.

yeah yeah well researched:

"The catch of the report was at the same time the mayor’s reason for the unusual action: Ottenstein is off the beaten path, it takes 20 minutes to drive to the next district town, almost an hour to the highway – that deters many people. The free building plots are supposed to lure them – and thus help against declining population numbers."

I no longer count that as the commuter belt. Even in old age, you need good infrastructure, hospitals, doctors, nursing companies.

that’s why our retirees in the neighborhood sell their spacious houses in the deepest Westerwald and move to us in the city.

When we are finally allowed to build, it is calculated so that we are almost done with the financing by the time I retire (since my partner is younger, he will still have to work then *g*). A house that is regularly maintained also lasts. I see this with my parents' house; even the windows, now about 40 years old, only a few had to be replaced on the west and north sides, once a new heating system, and I think that's not excessively much over 40 years. Of course, the house was maintained (for example, the wooden windows regularly received a glaze coat), but I think personally I won't walk this earth for more than 50 years, and that will also be enough for my younger partner. And then I'll say quite boldly: after me, the flood. Honestly: and if in my last years of life one or another window is no longer so tight, or I have a damp spot somewhere, I don't care. After me, they can tear down the hut. I only want to pay operating costs in retirement, no rent. The only way to have more pension without it being taxed. We finance in such a way that we don't push the limit. I still want to be able to live now; who knows if I will survive the next 40 years? I would kick myself if I now pinch every euro so that it will be better for me later. No one can guarantee me if there will be a later. But if I can finance in such a way that I would also pay the amount as rent and still have enough left to live on and the financing is arranged so that I am finished before retirement (and if earlier, even better!), then that's great!

For the nursing home, you should rather get a decent long-term care insurance. In my opinion, a lot of panic is being made about it.

money thrown away again for basically nothing. Insurances are basically there so that you don't need them and can "per se" never make a profit in terms of cost-benefit ratio (otherwise insurance companies would make a loss). The chance that you need insurance is ALWAYS significantly lower than the ratio of money intake to guaranteed expense (insurance premiums). So if the chance that you will need insurance is high, it is correspondingly expensive.
A house is still the best long-term care insurance. A house is a lot of tied-up money that you can't just spend casually. When the need for care arises, you can release this tied-up money (e.g., sell the house) and you are not a burden to anyone.

Regarding ancillary costs: heating costs are peanuts in a new building compared to the rest. In terms of cost-benefit factor, heating costs rank very high, unlike, for example, property tax, which has no immediate benefit.

in contrast, for example, to property tax, where there is no direct benefit.

But the city also has to build, maintain, and operate public facilities and infrastructure from something. So you also benefit.