House Renovation Construction Year 1955/1974 - Estimation and Feasibility

I am a big fan of old buildings, [...] I also don’t know how sentimental the value of the house is here. You also still have dad in there, who is surely supposed to stay there during the construction phase, right?

“Old building” is politely put “a big word” for a post-war little house, whose “older construction section” I consider steeped in sentiment. You won’t be able to simply demolish that; you will have to say goodbye to it with dignity. With a campfire where grandpa can tell stories of hard times. But the idea that you could carefully tape a whole extension around the senior would be an illusion. A temporary home for half a year will be the minimum.

I am also for demolition and new construction.
However, without father / separate apartment.

Perhaps it is easier to first renovate only part of it until dad is no longer around (which by no means is to say that this is desirable, it is just a consideration meant to be value-neutral) and then tackle the whole thing afterwards?

The father has already been hinted at as having beginning support needs that are no longer in the future – so I don’t see any “long delay” for the need to act. But shifting straight from construction stress – especially with own labor – into (in-law) family caregiving would be a trial (which the OP’s sister has likely avoided for good reason). Especially in a subsequently house size where one’s own children will be “waiting” spatially to inherit grandpa’s room. I see it as making all parties happier to look for solutions outside the seemingly most obvious spectrum.

It’s quite possible that you can still make something out of it using the existing building fabric, which often saves costs overall and is also better for the environment.

I consider classifying this property as still a “foundation” / “half the rent” a textbook Pyrrhic victory. Gently demolishing the roof structure is not hindered by the alternative of new construction.

I do think that a renovation is cheaper than a new build. But for that, the requirements for the property have to fit. A new build with 150m² living space * 2000€/m² plus additional construction costs would be more than double the renovation budget. In relation to that, the question arises how far €150,000 really gets you in terms of your wishes.

Changes to the floor plan, new floor, new underfloor heating, KNX, etc. definitely sound like the desire for new building standards. That would get very expensive. It would be better if, for example, one could keep already new radiators, gas heating, interior doors, front door, etc.

As I said, that's why in this case... you really need an expert. If they determine that the existing structure is already beyond repair, the construction was poorly done, and the effort is disproportionate, then demolition and new construction. But nobody here knows the house, we can only speculate.

Yes, old buildings honestly sound too good to be true. Anyone who knows these settlement houses knows what I’m talking about. The condition is simply not very good; everything was really built in the simplest way. The layouts, as here, are always designed for a lifestyle before the war. There were basically no bathrooms, but instead a large vegetable garden and a chicken coop. I have seen some of these settlement houses during my property search. As a rule, the plots are beautiful, but the houses are simply poorly constructed demolition objects.

We live in exactly such a settlement house. Great condition, although built in 1921 during lean years and only for workers. Laundry room, pigsty, large property. Bathroom was only installed in 1961, etc.

That's why I stick to the view that it must depend on the house.

As I said, that's why in this case.... you really need an expert. If they determine that the existing structure is already ruined, the extension was poorly done, the effort is out of proportion, then demolition and new construction. But no one here knows the house, we can only guess.

Exactly my opinion. Without an expert, you can't make any statement. And for me, there has to be some kind of additional storey. Without that, the thread starter basically has no own living space or bedroom, and depending on the building fabric, your budget is basically spent on that.

What I think should also not be completely overlooked: The next things will be due soon as well. In a new building, ideally, you have peace at first. With an old house, you won't get around permanent investments because something can always go wrong. Unless you finish everything perfectly. But then you might as well build new ;)

An important aspect is actually the father. With a lot of your own work, it will be a longer construction site. What will the old man do during this time?