The living space is approximately 8 m² smaller in the application drawings compared to the draft (GU).

As a rule, it is significantly more critical to exceed the framework of the previously planned exterior dimensions.

I can’t recall any case where 6cm outwardly would have limited a house construction. If you have to plan so precisely down to the last detail, the planner usually pays better attention. To me, this sounds more like a sleepyhead looking for a solution to keep the price down.

That is nonsense. If the KfW 40 was clearly communicated, the OP is in my opinion 100% right. What if the furniture had already been chosen to fit? Of course, what matters is what is stated in the contract. What exactly are you buying? If it says house with x square meters of living space, then the general contractor cannot just reduce that.

Thank you for your contribution. I’m copying a short excerpt from one of my previous posts. I just checked again. There is nothing more concrete besides the colored sketch.

"The contract only mentions what this could concern once: ‘Ground floor, in the size shown in the drawings, in the equipment according to the building description’ the same for the attic. As mentioned, at that time we only had the colored drawings. The more exact drawing was only provided after commissioning the architectural services. Furthermore, further back in the construction service description it states: ‘The dimensions contained in the construction drawings + building description are approximate values. In case of discrepancies between the construction plans and the building description, the building description applies; in case of discrepancies in the dimension specifications, the execution plans are authoritative.’

There is nothing else relevant here now."

The colorful drawing looks like it is from a catalog. That was the case with our previous row house as well. A sample drawing in a brochure explained the floor plan in a very simple standard. That this sample drawing was not corrected according to your wish to build a higher energy standard is understandable to me. The note about a higher wall volume would certainly have been nice. Have you spoken about the different wall structures for the corresponding energy classes?

So what I actually wanted to get at here: Should I open a can of worms with the general contractor now or is it "just like that" and I have to live with it?

Neither. It is not just a question of "complain" or "keep silent". You can simply ask and have it explained how the difference comes about. From the information available, I cannot see that someone is trying to take advantage of you.

By the way, your general contractor plans precisely in the octameter grid, so without stone cutting / botched work pockets. For that reason alone, many builders will envy you – at least those who go unprotected to a general contractor.

That is good information and explains the "growth of the wall volume inward."

Calculated in euros, that is about €22,000 less living space if we go by price per m²

This square meter price calculation can really become absurd. I recognize the sense as a basis for a rough calculation, but I do not agree to use it as a reconciliation tool for deviations in higher building standards. But if you briefly check the plausibility here, I can see that you are being offered a price per square meter under €3,000. That seems favorable.

By the way, I find it peculiar to speak of "guilt" and "victim" before clarifying the facts. That only provokes and brings no added value.

"The contract mentions what this could concern only once: 'Ground floor, in the size as shown on the drawings, with the equipment according to the construction description' the same for the attic. As I said, at that time we only had the colored drawings. The more detailed drawing was only available after commissioning the architectural service.

Well, quite vague. You can’t get it exactly as on the drawing anyway, because then the KfW values would not be met. In my opinion, that is already a misadvice. I am not a legal expert, but if you look at it strictly, the contract is probably void due to error or impossibility. If you want to rectify it, the cause of the problem cannot "cure" it to your detriment. But maybe I am wrong. In my opinion, any extension must always be made outwardly, if only because otherwise all other measurements no longer fit, such as stair risers, door widths, distances between walls, or even cupboard dimensions. Ultimately, the main question is whether you want to argue with your general contractor before the house construction even begins? So far, nothing has happened yet. I would simply go and say that the interior of the house must not become smaller and that he should correct that. Let’s see what he says then.

Well, pretty vague. You can’t get it like it is in the drawing anyway, because then the KfW values wouldn’t be achieved. In my eyes, that’s already bad advice. I’m no legal expert, but if you look at it strictly, the contract is probably void due to mistake or impossibility. If you want to fix it, the cause of the problem can’t "fix" it to your detriment. But maybe I’m wrong.

In my opinion, an extension must always be made outward, if only because otherwise all other dimensions wouldn’t fit anymore, like stair rise, door widths, distances between walls, or even cabinet dimensions.

Ultimately, the main question is whether you want to argue with your general contractor before the house building even starts? So far nothing has happened. I would just go there and say that the interior of the house must not become smaller and ask him to correct it. Let’s see what he says then.

Thank you for your contribution.

That’s probably how I will have to do it. And even if it only happens with considerable additional costs, he should please compensate by increasing the gable and knee wall by 6.5 cm. With the floor plan and area, we would be fine. It’s just that the reason we decided to sign the contract at the fixed price was based on the floor plan. We are also paying the additional €14,000 for KfW 40 to equip the house accordingly.

I will report back in a week what came of it. I doubt there will be a good agreement, but we’ll see.

Thanks so far to everyone and have a nice evening.

Oh, the floor plan/room layout/room location doesn’t need to be discussed separately. We are satisfied with it. We will build it exactly like my parents’ house.

The contract only mentions what this could concern once

It does not need to be mentioned multiple times in the contract. If you take it literally, you go through every sentence in a contract and consider what it means. If it is not clear, you ask. If everything is clear, you sign.
I certainly do not blame you, because we did not check every sentence back then either.
But you have to admit neutrally that the clause

Ground floor, in the size shown in the drawings, in the equipment according to the construction description" the same for the attic. As I said, only the colored drawings were available at that time. The more detailed drawing was only available now after commissioning the architectural service. Furthermore, it also says later in the construction performance description "The dimensions contained in the construction drawings + construction description are approximate values. In case of discrepancies between
the construction plans and the construction description, the construction description applies; in case of discrepancies in the dimensions, the execution plans are binding."

says exactly what I said and it is hard to believe.
However, the clause in the construction performance description dealing with wall thicknesses or the energy standard is actually missing now.