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

In the preliminary draft, it looks like the interior walls are 11cm instead of 17cm. Do you see it the same way? That would roughly result in a difference of about 1.5m².

The interior wall between the WZ and AZ also seems to have moved slightly upwards, which is to the detriment of the WZ, while the AZ remains almost the same despite thicker exterior walls (if I have recognized and calculated it correctly).

I simply uploaded the draft and the drawing for the building application here. Maybe that will make clearer what I mean. [ / ] Are these possibly acceptable now? Unfortunately, I couldn’t crop the more detailed drawing any better.

Above all, you should not crop out the upper floor, attic (and also the section for the building application).

By preliminary draft I mean the draft typically created with a general contractor before signing anything. For example, this one also did not have exact measurements per room but only as seen attached.

Oh, a pre-signature draft. Thanks! – now I finally understand how clients come to talk about a "preliminary draft" in obviously draft-less planning. The term actually means a scale sketch to show how the room program will translate into a concrete building mass, for discussion between client and architect or for a building enquiry at the building authority. So the planning in service phase 2 (which does not exist with the GC-draftsman).

However, I have to say: from memory, we upgraded to a then KfW70, and the external insulation was increased from 12 to 14 or 16 cm, but on the outside. On the inside, everything remained the same.

"One and a half shells" (construction masonry-insulation-plaster) is the usual approach.

Again: Look in the building specification and the contract, which we don’t know.

If the wall construction in the building specification does not achieve the desired U-value, that doesn’t help here. "Wash me, but don’t get me wet" (= replace aerated concrete in the construction masonry shell with calcium silicate brick without making it thicker or changing the insulation) cannot work. If the client then gives the GC the marching orders "EH40 rules," a larger-caliber total wall construction is preprogrammed. Without the additional note "Please apply increased thickness entirely on the outside," exactly what the OP complains about here will result.

In the preliminary draft, it looks as if the interior walls are 8 cm instead of 17 cm. Do you see that too?

The interior walls look unrealistically thin, yes.

What does the GU say about your specific inquiry, that would be the first step so that we don't have to guess here. He should be able to explain whether that is then okay or not, but this inquiry should definitely take place first.

What does the builder say about your specific inquiry? That would be the first step so that we don’t have to guess here. He should be able to explain whether that is acceptable or not, but this inquiry should be made first of all.

Due to the planner being on vacation, with whom we had clarified everything so far, no response has yet been provided. Along with the drawings for the building application, only the following was received:

"In accordance with the requirements for KfW40 and the (preliminary) specifications of our structural engineer, we have expanded the exterior walls from an original width of 42.5 cm to now 49 cm, and additionally planned interior walls in the ground floor according to structural engineering with b = 17.5 cm. This leads to a small loss of the actual living area, as well as small shifts of the interior walls according to structural engineering. However, this is absolutely necessary. We have – free of charge – expanded the captain’s gable in width, from an original width of 3.49 m to now b = 3.74 m. The reason for this is that the two supports on the ground floor must be designed with about 55 cm (structurally required), but so that the house entrance area does not appear narrow and small, and at the same time the supports are very massive and visually appealing, we decided on the enlargement."

I will know more next week.

Draft, typically created with a general contractor (GU) before anything is signed... this is not a catalog floor plan because we have drawn everything ourselves in advance (only with desired room areas, without exact dimensions) and sent it to the GU, who then professionally redrew the draft.

So the draft on the left was drawn by the "GU"? This is not a standard house, but a redrawn draft by the GU in good quality as a basis for the contract. It is obvious at first glance that this floor plan has little in common with an architect’s floor plan. I put GU in quotes because the GU is a company. The seller (not the architect) created the draft nicely using software here, and the architect then works on the draft after the contract is signed and adjusts it. This has happened here, and you are now surprised that the adjustments are apparently to your disadvantage because you keep calculating how high the square meters are.

In principle, everything is understandable. Only that you are now somewhat overreacting compared to what one would expect: just tell the GU that the architect should please correct the exterior walls—that is, the thicker walls used in the sketch—outward. If the plot is large enough and nothing already borders the limit, it should be feasible. That part of the house remains that part of the house for the GU. You have a fixed price. But as mentioned before: check the contract to see what is written there!

So what I actually wanted to get at here: Should I now open a case with the general contractor or is this "just how it is" and I have to live with it? The contract mentions what this could affect only once: "Ground floor, in the size shown on the drawings, with the equipment according to the construction description," the same for the attic. As mentioned, at that time we only had the colored drawings. The more detailed drawing only became available after commissioning the architectural service. Furthermore, further back in the construction performance description it says, "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 is authoritative; in case of discrepancies in the dimensions, the execution plans are decisive."

There is nothing else that could be relevant here now.