Cost to renovate a complete house

You mean retrofitting a controlled residential ventilation system in an old building? In the case of a major renovation, it's basically no different than in a new building, if you disregard that you can't embed pipes in the concrete ceiling (which I don't support anyway). You should take enough time and ideally keep the system in mind from the very beginning when planning the future floor plan (just as the bathroom should ideally be planned close to the supply lines or the heating). In our case, on the ground floor we get by with a 40cm deep partition wall (in the lower third a distributor, in the upper 2/3 a bookshelf) and about 1.5m² of suspended ceiling in the hallway and guest bathroom (also used for lighting). On the upper floor, 2 shafts of about 25x25 in the room corners were necessary. We also complement these with a built-in shelf so they don’t stand out. Otherwise, in our case, 4 core drillings of 300mm through the exterior basement wall and ceiling and some chiseling work are needed. Apart from that, the installation is nothing special. Underfloor heating is identical to new construction. You just might have to remove old screed beforehand. But that’s absolutely no problem and is even fun with the right machine (Tim Taylor grunt).

I see less own effort from us there, unfortunately, but still good to know that it is not so complicated

Don't get me wrong, we didn't do that ourselves, those were definitely the craftsmen.
What we did ourselves:

- Demolition
- Work on window openings and floor plan (beams, lintels, etc.)
- Roof truss (not the ceiling)
- Wooden beam ceiling
- Concrete slab
- Insulation of the top floor ceiling, basement ceiling, and under the screed

...then we lost the motivation and so we will probably only do the painting ourselves from now on.

However, if you don't want to afford a comprehensive TGA planning, you won't be able to avoid doing at least part of the building services planning yourself. The heating/ventilation installer will install a functioning system for you even without your help, but whether it will be ideal for your needs, or even particularly cost-effective in terms of purchase and maintenance, I would normally doubt.

Thank you for your tips, we are good at planning

We looked at the house yesterday. It is simply overwhelming because it is really huge. That’s why it scares us, because at the moment we cannot estimate the costs that will come up with this size. I will try to find some figures in the next few days. I think the property itself is a good offer. If you subtract the land value, you get a house with over 200m2 living space, about 100m2 basement, 2 garages, pool, photovoltaic and so on for (depending on how the negotiations go) 100-200k €. As a new build, we probably couldn’t afford it, the question is whether as a renovation project...

What is the relationship between the house and everything else to other objects in the area? If it is too cheap, I would be cautious. If you basically want to redo everything, then it won't be much cheaper than a new build? You list many points anyway, for the new build almost only "building up new walls" is missing.