Realistic financial planning for KFW40 prefabricated house?

Thank you for your answers!

You should tell us more about the old cellar, it might possibly be integrated into the construction project (?)

You seem to know an awful lot about cellars :-D Thanks for the tips.
The old cellar cannot be integrated. The house to be demolished is about 70 years old, the cellar is a solid concrete cast without insulation and about 2m ceiling height, but with a "3-chamber system"... So ideally, that thing should just be removed ;-)

a) What kind of planning do you mean there?

a) By "kind of planning" I mean that one should know roughly what the floor plan looks like, which stairs are suitable, which windows one wants... I can gladly upload my floor plan sketch.

b) In what way do you see windows as a cost driver per se?

b) So far, none of the providers really planned for nice windows. Only 1-2 double-wing windows included, white plastic. We would like at least 4 double-wing windows in anthracite with aluminum, which is already a few hundred € more...

For heaven’s sake, just no! - Promotional houses are aimed at people who are satisfied with choosing colors and moving around two non-load-bearing interior walls. All changes before the comma confirm the second gastronomic principle.

Regarding promotional houses: I am quite impressed with the selection from ELK so far, especially the ELK EH 155 comes very close to our idea. But you’re right: we actually only want to move a few walls.

What is the second gastronomic principle? :-D

... or KfW40 house + KfW55 cellar outside the "thermal envelope". In both cases, I would insulate the cellar ceiling as "new utility cellar" or "old utility cellar". And as always, I suggest thinking thrice about the avant-garde KfW fat level.

What do you think about the idea of insulating the cellar ceiling? Could you then leave walls and floor uninsulated? Or for example only the floor?
I have received cost estimates for a cellar of about 9x10m between €57,900 - €110,000 (always excluding earthworks) and cannot judge what is realistic. We would like to settle around €70,000. The groundwater is high at about 2.5m but does not constantly press (gravel base, old Danube floodplain). What can you realistically get for that money?

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Better do it the other way around: how much capital is available? You must surely have already been to the bank and know this.
Then subtract land costs including purchase incidental costs.
Then demolition and ancillary construction costs of about 30-40,000.
What remains must be enough for house, carport and paving. You apparently already have a garden.
If you calculate €2,500/sqm and take your room program, you will know whether a cellar is even in the budget.
Then you have to see which house provider qualifies: one builds cheap houses, another expensive ones. Since you also plan upgrades that increase the value of the house, you need to see where you fit.
Electrical work usually needs upgrading everywhere, but some house builders include more basement windows than others. One has already a fancy wooden door, another a cheap plastic door. You have to look at the construction service descriptions.

Attention: promotional houses are hardly modifiable. At least in the prefab house sector.

Thank you! Yes, we have discussed the "final" framework of the construction project with the bank.
My problem right now is the complexity: you CAN build without a cellar, but then the house has to be correspondingly bigger, which also costs money. Are you saving in the right place there? We would prefer a cellar, but if it becomes significantly more expensive than €70,000, that simply isn’t doable and I need to plan an alternative in time.
Good advice is hard to get here: I have received prices between €57,900 - €110,000 from the prefab house manufacturers. And I don’t know whether €57k was a teaser offer or conversely whether €110k includes unnecessary costs (residential cellar) or a fat commission.

One CAN build without a basement, but then the house has to be correspondingly larger, which also costs money.

Usually, one builds a utility basement, as you are planning. If you assume 80 sqm ground floor/upper floor area, then you build 80 sqm just for freezer storage and utility room plus an office, which is cumbersome for a utility basement… but even 65 sqm just for utility is practically unusable! There is also the attic for use, so you end up with a surplus of usable space.

Prices between €57,900 - €110,000 were quoted by the prefabricated house manufacturers.

Bare or finished - the values mentioned fit.

In the close family, someone is currently gathering offers.
A cellar for 9x11 with Kfw55 is between 85k-100k for them.

It's about a utility cellar, however with stairs, water connection for washing machine, some power outlets, floor coverings...

The basement is a thick concrete cast without insulation and about 2m ceiling height,

My problem right now is the complexity: you CAN build without a basement, but then the house has to be correspondingly bigger, which also costs money.

Yes, then everything is clear: build without a new basement, save the demolition of the old one, you have the house entries right there, the eighty saved (with insulation under the ceiling) is completely enough for the house connection room and storage room.

b) So far, hardly any of the providers have really planned nice windows. Only 1-2 double-wing windows included, white plastic. We would like at least 4 double-wing windows in anthracite with aluminum, that's already a few hundred € more...

What now, "nice windows" means double-wing anthracite? - for the saved basement demolition, you can take aluminum all around and still have money left for the walk-in rainshower and a garden shed.

What is the second gastronomic principle? :-D

"Per***s costs extra".

with the then still cumbersome office for a utility basement…

What exactly do you mean by that, is an office in the utility basement not possible? Or just "unsightly"? It’s supposed to be more like a kind of "man cave," so I don't need big windows in the basement ;-)

Yes, then everything is clear: build without a new basement, save the demolition of the old one, you already have the house conduits there, the eighty-one saved (with insulation under the ceiling) is completely sufficient for the house connection room and storage room.

No, unfortunately not. The thing is almost a bunker and with that you really can’t do anything other than tear it down... There are also no connections in there, no water, no sewage, no electricity. But as I said, there is a 3-chamber system (an old sewage treatment plant...). You get down through a passage that is about 1x1m and a kind of staircase (concrete projections about 30cm and 10cm wide). The previous occupant of the house had a rather rustic lifestyle, obviously without running water (we didn't find a shower in the house, but there was a pit toilet that, as mentioned, ended in the basement). It’s a bit hard to imagine if you haven’t seen the basement in person, but please believe me: you can’t and don’t want to use it anymore...

So what can I achieve with €70,000 regarding basement construction and where can I save?
Utility basement? Insulation of the basement ceiling? Insulation of walls and/or floor? Retrofitting the finish myself?

What exactly do you mean by that, is an office in the utility basement not possible? Or just "not nice"? It is supposed to be more like a "mancave", that's why I don't need big windows in the basement ;-)

It is difficult to create a living room in a utility basement.