Renovation or demolition and new construction - decision support from the architect?

In addition, demolition and new construction (140m² without basement)

then the old basement should remain and the new house be built on top of it?

then the old cellar is supposed to remain and the new house built on top of it?

This is often a practical economic solution, unfortunately the facts are missing here for all perspectives.

We completely renovated and extended a settlement house from the 1930s, and it turned out really beautiful. When you renovate an old house, you almost inevitably come up with creative solutions that often have much more character than a new building. However, the effort can be disproportionately high, both in terms of time and costs. We took 2 years and had pure construction costs of 3000€/m^2 – and that was in 2019, when a new building was still calculated at 2500€/m^2.

We also renovated a slightly larger settlement house and were under 2000€/sqm in 2023/24. We did not touch two points: the exterior facade was only painted, but not insulated (it already had 8cm), and the basement was not dug out, only the basement ceiling was insulated. Everything else completely new (electricity, pipes, roof (roof structure was still okay), windows, floors, ...), many floor plan/window changes, etc. Also quite more expensive fittings (large-format tiles, etc.).

Renovation for 3500€/sqm must have some special features?

Yes, a renovated house has disadvantages because in some aspects it is still an old house. But as others have already noted, I also think it has significantly more charm.

Wow, thank you all very much.
I am overwhelmed by the amount of feedback.

Sorry that I didn’t come with photos and floor plans right away.
I promise to do better and will make sure to provide them promptly.
Here is already a photo from the outside:

Since you are worried about heating costs, that is certainly an issue, but as an example with us, built in 1950, 2 apartments with a total of 4 people permanently living on about 200m2, 250m2 (partly not permanently inhabited).
Costs 3000€ last year. Could be more in a harsher winter. We will probably get a wood stove now. Purely monetarily I still don’t think insulation pays off for our large house. When the roof needs work, we will insulate it, but we will only do the facade if we are forced to do so.

I actually find the indoor climate better as a previous poster already mentioned, than in some new buildings. In summer it is noticeably cooler thanks to the thick walls and ventilating at night.

Thank you for your experience. The seller told us that the oil heating consumes about 3,000 liters in one winter.
But we are already noticing the positive coolness: whenever we go to air out, we go from summer temperatures into a pleasantly cool house.

This is regularly done with damp basements, does not cost that much. Of course, you can’t get under the basement floor, but if there is no office or something like that going there, it doesn’t matter. Insulating the basement ceiling is also possible if there is enough ceiling height.
In a living room without a basement, just install underfloor heating, then you won’t have cold feet.

That’s good to know, thanks. The basement should stay a basement; your comment about the living room without a basement definitely makes things easier for us.

So the old basement is supposed to stay and the new house built on top?

That is often a practical economic solution, unfortunately the facts are missing here for all perspectives.

If that works, yes – I had naively assumed until now that this is uncommon and generally not advisable.

We completely renovated and extended a settlement house from the 1930s and it turned out really nice.
When renovating an old house, you almost inevitably come to creative solutions that often have much more character than a new build.
The effort for this can be disproportionately high, both in terms of time and costs. We took 2 years and had construction costs of 3000€/m^2 – and that was in 2019, when a new build was still budgeted at 2500€/m^2.

We also renovated a somewhat larger settlement house and were under 2000€/m² in 2023/24. We didn’t touch two points: the exterior facade was only painted but not insulated (it already had 8cm), and the basement was not dug out but only the basement ceiling was insulated. Everything else completely new (electricity, piping, roof (roof structure was still ok), windows, floors, …), many floor plan/window changes, etc. Also decidedly higher-end fittings (large format tiles, etc.).

Renovation for 3500€/m² must have some special features?

Yes, a renovated house has disadvantages because in some aspects it still is an old house. But as others have noted, I also find it has much more charm.

Interesting, did you know right from the start that it would be a renovation in your case?

If that's possible, yes – until now I had naively assumed such things are unusual and generally not advisable.

Sprinkling questions with facts only in homeopathic doses is indeed generally not advisable. Using a basement storage is often a good idea, but it's simply not a million-seller because many buyers of developed plots tend to blindly clear them. For some people, building is still not expensive enough. This has to do with the fact that a generation of spoiled single brats is now entering the age of building their own homes. They are used to specially finely tuned wish concerts. And again: create the basics first, then you can be advised – secretly personally or publicly publicly.