High construction costs with rising building interest rates

Above all, it is a matter of expectations. It already sounds like you want to upgrade an old building to current standards. Or build new, then of course to the latest standard. And that is expensive. Or you settle for an old floor plan and can live quite wonderfully in it. Even if it is not perfect. And then, as the OP, living in the countryside in Lower Saxony with a house from the 90s, you are clearly below 450k new build price. And that was what this was originally about.

Well, is it really a good sign if the aforementioned average-earning couple can just about afford a little house from the 90s in one of the areas with the cheapest income-to-purchase-price ratios? We have a shortage of living space and would actually be dependent on these people as builders to expand the supply of housing.

Apart from the fact that there first has to be a significant number of these still not worn-out houses from the 90s. Especially in rural areas, houses tend to be lived in until the bitter end, which is why the majority of the current supply dates from the mid-60s to early 80s. The technology is often still unchanged in its original state. Especially in the "younger" construction years, still with the original bathroom (or even original kitchen). Unfortunately, it’s no longer just a matter of a few cosmetic repairs when the rooms only have 2 sockets and any RCD switches are missing. On the other hand, I consider floor plans overrated anyway. There is a lot of fashion involved, and ultimately each phase of life requires different floor plans, especially with children. What is ideal for small children is a nightmare for teenagers and vice versa.

In urban areas, houses from the late 90s are more likely to be offered because young retirees downsize after their children move out. However, these are not available for 400 thousand, but rather for twice that amount. At that price, even most high-earning academic couples are out of the running if the family financial background is missing. We don’t even need to talk about average earners.

What kind of arguments are those?

I ask myself the same..

Also an important point: The number of children. In my youth, 3-child families (probably not in the big city, but in my environment) were still absolutely common, only children the rare exception. A family of five needs a bit more space and of course 160m2 would be comfortable, but not a luxury now. Especially without a basement, which was common 30-40 years ago.

At the latest here you contradict your own topic, sometimes like this, sometimes like that.

that even in a "cheap" market with solid purchasing power in the countryside a young family can hardly afford a house anymore.

In the metropolis that costs you a million,

Who is even talking here .. oh, somehow you are in the wrong thread after all.

Well, I also never had more than 200 euros in heating costs per month in the 60s apartment

And now I have 25 € per month in the house, so about 2,100€ less per year than you in the old place.

And I now pay 25 € less per month in the house, so about 2,100 € less per year than you do in the old place.

You don't have that. You are probably offsetting your state-subsidized feed-in tariff against it, which has nothing to do with the required heating energy and primarily occurs in summer. In winter, this barely covers any electricity for your heat pump since the low yield is already used for other household electricity. Just for hot water alone, you need 25 euros of electricity per month (okay, sunny months are included), or does your family always shower cold? By the way, I also live in an energy efficiency class A property... so I do have a comparison. Double living space remains double living space, even if it is naturally more efficient.

But even if that were actually the case for you: have you calculated what the facade insulation, ventilation with heat recovery, photovoltaics (which by the way cost insurance annually, even the smart meter is mandatory), and the heat pump have cost you in total? You will never recoup that over their lifespan. The opportunity costs of the tied-up capital alone are higher than 200 euros per month. Economically, it will never work out.

Of course, if the CO2 pricing skyrockets as feared in the worst-case scenarios and heating costs actually multiply, then there will eventually be a financial breakeven. But currently, no one should be advised to buy a used single-family home anymore. At most, please only a new townhouse.

In the past, having your own house was also a given for the broad masses, and the social differences arose in the equipment of the car, the holiday trips, and the car that was driven.

Sorry, but how can anyone claim such nonsense. Where did you read that, because you have never experienced it yourself. I just can't believe how some people eagerly talk themselves into their own depression or love to see themselves as disadvantaged.
On the topic of teachers: I am not a teacher, but if everything is so great, why didn't you become one, because then your life would be great immediately. What do you do for a living?

The existing property is okay for a craftsman, but whether a heat pump without extensive renovations makes much sense, I have my doubts. With small radiators it does not make sense, and just hanging bigger ones (apart from the fact that it is ugly) also does not work because the windows then usually reach accordingly deep. So only underfloor heating remains, and that is not always straightforward to install in existing buildings (insufficient screed thickness), even in properties that are only a few decades old. It therefore strongly depends on the individual case.

Tell me, do you read this stuff again before publishing? With existing properties you are basically forced into expensive underfloor heating because you cannot fit radiators in such a house. Also, you were not allowed to become a teacher. You sing your misery quite strongly, that is simply confusing what you are telling here, and I also understand why with such a mindset you have to feel cheated or constantly disadvantaged.

Sure, with rising CO2 pricing, this will multiply,

You are getting yourself worked up: No, the €200 heating costs you mentioned might increase because of that, but certainly not "MULTIPLY" or are you going to pay €800 heating costs in the same apartment in the future? Stay grounded and at least use somewhat realistic scenarios.

Sure, there are technical solutions to minimize this efficiency loss, but they are also correspondingly expensive and therefore unattractive.

A controlled residential ventilation is by no means unattractive, but is already standard in new houses in case you missed that. I recently spoke on the phone with a young building owner here from the forum who is installing the controlled residential ventilation himself and he is not a trained craftsman but sharp. Just a tip for you.....

Those who want to save ancillary costs and still at least have a small garden should at least choose a terraced house.

Good idea, but how do you suddenly go from baking cakes to baking butts? Sorry, I don't want to offend you but that really seems as if you were furious right now. You go from the flattered teachers to forced underfloor heating and the multiplication of heating costs to the suddenly sensible terraced house. No one probably thought you were a "Green" (quote) until then anyway; that statement of yours was unnecessary.

And even in the countryside, where it maybe "only" costs 500 thousand, it is hardly possible with 5 net without significant equity. As soon as children come, it no longer stays at 5 net, but income falls and usually not only temporarily.

I live so much in the countryside here in a new development with 10 new single-family houses. Most of them have a rather "simple" job and certainly not all inherited millions and yet have children and a house. So your statement as a blanket truth is easily disproved within a 100-meter radius.

Yes, that is somewhat generalizing.

Unfortunately almost everything. What also causes your partly good or justified arguments to disappear in it.

Once again: Self-performance is great, but you also have to be realistic. What can the average person still do nowadays and how much time can be invested? Especially as a DIY beginner you have to bring time to learn things.

Exactly that was explained to you by up there, but you don’t want to hear it, you want to suffer and you go from asbestos to radiators to having children. Do you work as a Duracell bunny on the side?
Row after row people here tell you what and how they did it THEMSELVES and you ignore it and move on to the next drama. Do you think these people are just dreaming what they are telling you here? They don’t babble for days but act and solve their problem.

Once again: Self-performance is great, but you also have to be realistic. What can the average person still do nowadays and how much time can be invested?

As already said above, you apparently lack the will, this is just a cheap excuse.

I consider floor plans to be overrated anyway

Uffff

and the heating costs actually multiply,

Again. Somehow everything seems to be rubbish to you, which of course everyone else made up again and the satisfied home builders and renovators are all fakers without any clue. Take a few sips of valerian or try emigrating, that is also popular with those who always feel disadvantaged.
Professional advice: But they are always quickly back from their respective paradise, where people like to hear whining and chronic self-pity even less.