Assessment of construction costs for a single-family house in NRW (current situation)

Exterior walls + insulation + interior walls are calculated with a thickness of 0.4 for us.
-This results in a minus of the interior area of about 17-18sqm...

So it's about ~143sqm, including hallway / stairwell

Now just show the plan...! Or is it so secret? Your calculation can’t be right, do you want help or just to be generally correct?

Edith: 12.1*8.9 = 108 - 10% walls etc. = about 97m2.
You mentioned 130m2 as living space: 130 - 97 = 33m2 for the upper floor.
Square root of 33 = 5.75. Your upper floor is therefore 5.75*5.75 meters in size... nice.

Illustration attached ;)

Have I overlooked something?

What makes the space under a sloping roof only half as expensive?

Air-to-air heat pump

KfW "thingamajig" or standard? Probably not passive.

KfW "whatchamacallit" or standard? Probably not passive.

Vaillant VWL 115/2 aro Therm air/water 8.4 KW according to our construction specifications

Vaillant VWL 115/2 aro Therm air/water 8.4 KW according to our building performance description

It is not really the answer to my question, but at least LLWP was changed to air-water heat pump, which is why I asked about the building. ;)

@ No, no slope...

@ So the 1.5-story part is not considered at all in the calculation? In other words: (8.9m x 12.1m) * 2 = 213.6 sqm .. ?? 213.6 sqm * 3000 = €640,800 + €100,000 for the basement + 10% incidental costs + extras.. .? Seriously?

@ What are the incidental building costs of €50k.. ? As far as I know, the incidental building costs already include the architect (without construction management function)..!?