New single-family house or core renovation of a house built in 1978

Ok, that is really crazy cheap. Congratulations on managing it like that. I have seen quite different things, which in my opinion are rather the rule. If someone then thinks they can do it that cheaply too and the money runs out halfway with no buffer, their existence is quickly threatened, so it's better to have something left over in the end.

These are indeed price drivers.

That's why I asked what exactly is supposed to be done. And if the floor plan fits and/or chimney flues don't disturb or plastic on the outside wall isn't a big deal, it already helps tremendously.

There are always very different ways to renovate. One example with flooring: Either you tile nicely and cheaply over the old covering and then have a small mini-step at transitions, or you remove the old covering first and do everything new. It's a personal decision how annoying you find this mini-step that wouldn't exist in a new building. (Floor heating issues are excluded in this example.)

This can apply to all trades.

A new bathroom in "new building quality" can become very expensive if you insist on a barrier-free shower entrance but neither the drain lines are present nor sufficient floor height is available. But what can you do if a shower tray with a rim is no longer modern and does not represent "new building quality"?

The electrical wiring is probably already 3-core. That means extension and not a complete replacement. Windows may possibly have already been done. Or a glass replacement is worthwhile. Heating is the question. Water and wastewater are interesting. Steel pipes should be removed and replaced. Copper can stay.

I expect only an extension for the cable network and the number of sockets here, but a new meter cabinet. Windows, yes, probably glass replacement, partly new seals and readjustment. The house is a bit too young for cast iron drain pipes.

But what can you do if a shower tray with a rim is no longer modern

I look forward to my shower daily with foot lifting when getting in and out. Little things also cause trouble, that applies to fitness as well.

I look forward to my shower every day, lifting my feet when getting in and out. Every little bit helps, that also applies to fitness

Well, if that's the case, then just shower in your bathtub

It really depends on what needs to be done and what is intended. I haven’t finished analyzing the numbers yet, but quite a sum is already coming together. Roughly for everything new (approx. 225m²): gutting 50k, heating/plumbing/controlled residential ventilation 75k, insulating and reroofing 50k, electrical 30k, ETICS 30k, windows/doors 35k....

I have completely built a shell construction (walls, floor slab, and roof present, nothing else). I think it cost about 1000€/m². I find it, sorry, unjustifiable to tear down a house that "is fine." The floor plan fits, the size fits, good substance – just for ecological reasons alone, I would always renovate. Throwaway society with houses... that's how far it comes.