Renovation and expansion of the parents' house

Thank you very much in advance.

If in the end it is only €200,000, of course I am not upset, but generally it feels to us like building a house and we also do not intend (of course at the current time) to build an additional house.
That is why the extensive work and also the estimated budget of €250,000, which would certainly be needed when building a house.

I would really think it over. Especially with a renovation, there are often so many surprises under the plaster that you don't expect and suddenly they create holes in your budget...

We also considered whether to renovate or tear down, in our case it was a two-family house from the 1950s. In the end, we tore it down and completely rebuilt. In the renovation, we could have hardly left anything standing except for the exterior walls and wouldn’t have wanted to. And heating, electricity, water, roof, insulation, etc. would all have had to be redone.

As mentioned, the ground floor will remain. The first floor is to be rebuilt, here more or less only the exterior walls would remain. The second floor is then a new construction on the existing solid ceiling between the first and second floors and a completely new roof on top.

At the moment, basically only the roof structure stands on the solid ceiling in the second floor and must be renewed anyway. That means, for us it then appears that "our" first and second floors will be new construction.

Would that work structurally? So the "old" ground floor would then support the two fully developed and renovated floors?

And how about the room layout? Normally, for example, load-bearing walls must run one above the other in the middle of the house so that the roof beams have somewhere to rest. Or you need steel beams or something...

Unfortunately, the costs are very difficult to estimate...
What about the heating? Does that all have to be redone as well?
What about electrical and network cables? Would you then have the "new" electrical and LAN/SAT cables installed together on the first floor?
Water? Are the pipes from the basement up to you suitable to heat and supply all of this?

Apart from that, of course you need all the interior fittings that a new building requires. You just save on the "foundation slab" and what needs to be dug outside for the supply lines.

We are currently still in the phase of planning for "us," meaning we have not yet had a structural engineer or architect on site.

Basically, there should be no problem regarding the structural engineering, as the house was built in solid construction, not by the developer using quick construction methods. The expansion of the 2nd floor was basically planned for an unspecified later date.

The room layout is of course planned but not fixed yet. Load-bearing walls are taken into account. A pillar in the living room would also be conceivable. Since the 2nd floor is completely unfinished, the structural engineering must of course be considered there as well. Whether to build up in solid construction or timber frame construction is not yet decided. Regardless of the method, we are completely free there, so the roof beams will find their place.

I cannot make any statement about heating/electricity/water at the moment. Normally, those can be built upon. The existing heating system has 26 kW and should be sufficient.

Somehow I have the impression that a wrong picture has formed here from the beginning. This is not a shack. Ultimately, it is about adding a floor to the house and simultaneously carrying out necessary and long-term forward-looking work such as insulation, sealing, and designing according to our wishes so that we do not have to renovate again in 5 years.

We are not only saving the foundation slab and supply lines. It is usual for us to build with a basement, even though many no longer do this for cost reasons. That means these costs are saved as well. Additionally, we possibly save demolition costs, and the investments in renovating the ground floor are not wasted. Furthermore, in the case of demolition and rebuilding, my parents currently living in the house would have to be relocated during that time, which would cause costs (and even more nerves).