KFW 70 or is KWF 40 Plus worthwhile with significant additional costs?

The main time is saved by using fast screed. In other words, walkable after 24 hours and quite quickly ready for covering.

That's not quite true. Most general contractors building around here have such a fast screed, also with us, and still need 6 months. It's interesting that they still manage it in 3 months. At the moment, all you hear is that all possible general contractors are extending their contractually agreed construction times from 6-7 to 9-10 months.

Viebrockhaus simply has many own people, so they don’t have to build in buffers for when the window guy can only come three weeks later. When they start, all trades are scheduled at the right time. Then a well-coordinated team and practically no possibility to disrupt the process with own work in between. And there are also far fewer delivery problems with materials due to the rather limited selection.

Basically, one has to ask the question when the additional investment is supposed to pay off. If you are already 45 years old, insulation logically has a lower priority than a 25-year-old builder would see it.

We have taken a middle ground and done KFW54; heating costs of 28-31€ are the result. Pessimistically, one can assume an annual increase of 5% in costs. If the situation worsens and more and more electricity has to be generated by gas (shutdown of nuclear power plants, electromobility), this could become even worse.

Based on the 5% price increase and 30 euros monthly: Here I am at a factor of 11 heating costs after 50 years (330€ monthly). At that time, the 75-year-old is retired and still has to financially hold on. Another 10 years later, the person is then 85 years old and has to pay a factor of 18 (530€ monthly).

Assuming the heating costs today were already 100€ instead of 30€, the 85-year-old would even have to pay 1800€ monthly.

It does not have to happen like this, but it can... we live in Germany! Who would have expected 60 years ago what fuel costs today? Back then it was around 25-30 euro cents.

....We have taken a middle path and built to KFW54 standard; heating costs of 28-31€ are the result....

The standard is new to me :-P

Pessimistically, one can assume an annual increase in costs of 5%. If the situation worsens and more and more electricity has to be generated using gas (shutdown of nuclear power plants, electromobility), it could even get worse.

Based on the 5% price increase and 30 euros monthly:
Here I am after 50 years at a factor of 11 heating costs (330€ monthly). At that time, the 75-year-old is retired and must still manage financially. Another 10 years later, at 85 years old, the factor to pay is 18 (530€ monthly).

Assuming that heating costs today were already 100€ instead of 30€, the 85-year-old would even have to pay 1800€ monthly.

It doesn't have to come to that, but it could... we live in Germany! Who would have expected 60 years ago what fuel costs today? Back then, it was equivalent to 25-30 euro cents.

But it might not happen like that... we all don’t know! But to take your example... 30 cents, 5%, and 60 years... we would be at roughly 5.60€. But the liter doesn’t cost Super Power Ultra High Efficient or anything like that.

Maybe technology will also develop further and we will generate cheaper electricity again in the future? Heat pumps have a COP of 10? (Sorry, I’m not particularly technically savvy) I don’t know. But in such calculations, you can factor in all kinds of things. Everyone has to decide for themselves whether they tend more towards the Club of Rome or rather the idea that it’s not as bad as it seems.

That’s why such questions can’t really be answered generally.

It doesn't have to happen that way, but it can... we live in Germany! Who would have expected 60 years ago what fuel costs today? Back then it was about 25-30 euro cents.

Yesterday there was a nice report about it on mehr BR gesehen (it was a quer a few weeks ago). The average purchasing power was also much lower back then. In other words, today you can afford significantly more gasoline than back then. And that despite fossil fuels becoming so scarce.

Basically, you have to ask yourself when the additional investment will pay off.

Right. And to be honest, that also includes considering what it means when the capital is practically tied up. This is often forgotten.

If I just put the extra 30,000 euros into ETFs... oh well...

Based on the 5% price increase and 30 euros monthly: Here, after 50 years, I am at a factor of 11 heating costs (330 euros monthly). The 75-year-old is retired and still has to manage financially. Another 10 years later, he is 85 years old and has a factor of 18 to pay (530 euros monthly)

Yes, that’s the milkmaid’s tale. Looking at something like this without adjusting for inflation/purchasing power is just balm for one's own conscience.

Also, one must not forget that over the course of these 60 years, quite a lot has to be invested. Significantly less with a gas boiler than with these new technological wonders.

You are right, but everyone understood what I was getting at! That is already good.