Settlement house 1954 - complete renovation possible?

Yes, that's true, it is expensive and takes a lot of time. Nevertheless, I would prefer to do it if the plaster is already older (let's say older than 30-40 years), because it simply creates a lot of dirt and work, and that's something better done before you live inside. And yes, it is also noisy if you don't do it manually and plaster by hand. But back then, we simply didn't have the budget and especially no time to do it.

Oh yes, regarding your specific questions:

[*]Feasibility: The basement floor slab will remain un-insulated. -> Does the KfW 55 energy saving concept collapse because of that?

It depends heavily on the energy consultant, you have to find one anyway, also for the 430 individual measures. It probably won’t be worth it, as the general trend shows here. First see if you can achieve KFW-115. The rest is a bonus.

[*]Have we overlooked a big cost risk?

Definitely (painting work, stairs). Many things only become visible once you’re inside. We found damp walls due to a leaking balcony. That could be dealt with well through external insulation, but a balcony is poison for the KfW energy house, as it is connected to the floor slab. So again expensive insulation, tearing down the balcony or no KfW efficiency house.
Maybe you also want extras like a fireplace?

The most important thing missing from your schedule is a buffer. That should be €30,000 or more. It’s enough if due to lack of time you have to subcontract the electrical work plus a bit more and the buffer is gone.

[*]Is 12 months (provision interest) sufficient time? Although I am reasonably skilled in handiwork, unfortunately, I no longer have the necessary time.

If you have no time, then you have to seriously question all items involving your own work. With children and increasing distance between current residence, work, and renovation site, it’s so individual that anything between a few months and two years of construction time is possible. Besides time, physical fitness, friends, family, advisors, etc., also vary greatly. I do my own work almost exclusively alone (even without my wife), so I will need a little over one year. Currently, I am rather relaxed, as the building permit will still take some time.

Anyway, don’t be discouraged here; such a renovation can be a great project. However, I would strongly recommend leaving gimmicks like photovoltaics completely out, unless you really still have money left over from the buffer. You will only know that once you are in the middle of it.

Hello? This is absolutely amazing! I even just found an identical showcase in the basement of a customer - it's free, my wife is in seventh heaven

Uh, yes, I certainly didn't mean that this was a remorseful renunciation - on the contrary: you first have to find the charm in that condition (as is also the case with the caravan) - and a wife in seventh heaven is priceless and tops any jacuzzi with ambilight, Bose surround, and Veuve-Cliquot tap system

Wall removal/replastering/painting ___ own work ___ 8000

What is this item for? - I expect the wall between the kitchen and the child’s room on the ground floor to be completely removable without replacement, while the one between living and sleeping areas, on the other hand, I consider not load-bearing but bracing*. I note that I see the crucial question against the background that layout modifications are limited to one or two decimal places.

*) in practice, this is by no means cheaper: "load-bearing" could be replaced by steel beams, with "bracing" it’s trickier

First of all, thanks to everyone for the many contributions! Definitely gives us a good feeling. If we carry this through now, there will of course also be illustrated updates here.

We had companies do the following for us: tiling work in 2 bathrooms and the tile backsplash in the kitchen, complete electrics in a simple version, new radiators and piping (water, sewage, partly new lines, outdoor faucet, also new lines in the basement), 2 new roof windows, roof insulation from the inside with drywall cladding.

New radiators means normal radiators that hang under the windows? I’m considering in the planning whether underfloor heating on the 1st floor (where the bathroom is) wouldn’t be nice, but then a very flat system would be necessary.

Guaranteed (painting work, stairs). Many things only become visible once you’re inside. We found damp walls due to a leaking balcony. That could be fixed well with the external insulation, but a balcony is poison for the KfW energy house because it is connected to the floor slab. So expensive insulation again, tearing down the balcony, or no KfW efficiency house.
Maybe you also want extras like a fireplace?

The most important thing missing in your list is a contingency fund. That should be €30,000 or more. It’s enough if you have to contract the electrics out due to lack of time plus a bit more and the contingency is gone.

There is no balcony. The pit at the back is used for rainwater – that would also have to go for the insulation. The thing with the contingency fund is probably true. I also plan to continue saving hard so that around €10k will be available again within the first six months. Then there’s also a building savings contract from way back with about €5k and in the worst case extras like the photovoltaic system will be cut.

Does a fireplace work well if the house is optimized for airtightness and insulation?

If you don’t have time, then you have to seriously question all positions involving self-performance. With children and increasing distance between current residence, work, and renovation project it is so individual that anything between a few months and two years of construction time is possible. Besides time, physical fitness, friends, family, consulting people, etc., also vary greatly.

Luckily we only live 100m away. Unfortunately, family is out due to distance.

What is this item intended for? – I expect the wall between kitchen and child’s room on the ground floor to be removed without replacement; the one between living and sleeping I consider, while not load-bearing, to be bracing*. The said crucial question I see, mind you, against the background that layout changes are limited to one or two decimal places.

That might be a good point. I will talk to the structural engineer about it again because the possibly bracing wall should definitely be removed. The high costs were estimated due to possibly necessary supporting elements.

Fortunately, we only live 100m away. Unfortunately, family is out of the question due to the distance.

That means you know the residents / sellers from chatting at the bakery?

I will also talk to the structural engineer again, because the possibly bracing wall should definitely be removed. The high costs were calculated due to possibly necessary support elements.

A structural engineer should be able to interpret the wall thickness specification "10 cm" especially in the overall context of the floor plan, and not have read less into it than I have.

That means you know the residents / sellers from chatting at the bakery?

A civil engineer should be able to interpret the wall thickness specification "10 cm" especially in the overall context of the floor plan, and shouldn’t have read less into it than I did.

We know some of the family by sight, but the children don’t live around the corner. The whole thing actually came about through friends in the neighborhood.

That means the civil engineer should be able to assess that just from the plans, right? Are there also cases where a floor or wall is opened to measure the thickness of elements? That would probably be difficult to do immediately before the purchase.