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

You write that you feel deceived, but you do not provide any evidence even upon request - neither regarding the "colorful pictures" which you name as your basis for decision, nor on a specific clause in your contract that guarantees the living space according to your expectations. So no one can help you except getting upset and writing "oh, that is terrible" and suggesting demands which they do not have to support and which are not enforceable. I would consider it harmful to reinforce someone in false assumptions, and I do not want to harm anyone here in any way.

You did not want to understand or did not understand what I wrote. We both know that already.

I have uploaded all the sketches and written all the relevant passages from the offer and the construction service description here. There is no fixed living area guaranteed in the contract. However, there are the sketches that were created for me before signing the contract, including room areas according to DIN. Those surely cannot be invalid, right? What else should I base my decision for or against on? If I see a campervan with a roof extension in a VW brochure before purchase, I certainly will not accept one without it upon delivery.

You didn't want to understand, or didn't understand, what I wrote. We both know that already.

Yes, yes, I do understand. You consider it usual to enlarge the exterior walls inward because everything else would be an unreasonable effort for the builder. And that's nonsense.

I want to see the clause in the contract that states that the promised square meters are reduced if you want thicker exterior walls.

I am speechless. Certainly, when a wall is already standing and is 2cm too far to the left or right or the window is 5cm too far to the left. Never mind, you can't change that anymore without much effort. But if the planning just subtracts 6% of living space because he doesn't want to recalculate the static? I would look for a new building partner, that has nothing to do with fairness. He simply doesn't want to, and that will come back to bite you more often during the construction process.

That’s exactly how I see it too, thank you. I still don’t quite understand what is not comprehensible about my case and which details are still missing here to prove that I’m simply a bad person trying to fool the general contractor. I have described everything as it happened. I have hidden nothing.

From your point of view, you are right.

The general contractor naturally sees it quite differently. He wants to save costs. Either for profit maximization or loss reduction.

Therefore, understandably, he left the external dimensions unchanged.

A rogue who thinks something like this happens by accident.

Does the property and the development plan allow for enlarging the house?

In my opinion, by commissioning the additional costs due to KfW40, you commissioned the change in wall thickness. But in no way did you agree to a reduction of the living area.

You could, because of the reduction of the living area, claim a cost reduction. The general contractor would (will) also claim additional costs due to the increase of the external dimensions. The dimensions were declared as binding in the contract. But in my opinion, not the living area.

I am curious about the outcome.

But there are the sketches that were created for me before signing the contract, including room areas according to DIN. Those surely can’t be void, right?

That is exactly the point. Were these sketches made specifically for YOU, or are they sample sketches generally used when deciding on the house type / floor plan? In connection with the clause from the contract you quoted "taking precedence over drawings," this is precisely what determines whether you can derive a claim or not.

that I’m simply a bad person trying to fool the general contractor.

It is certainly not my intention in any way to judge you. You will not find a single word where I do that – verifiable.
I absolutely do not want to encourage you to run headlong into a wall out of anger and disappointment. I would find that unfair. Some things are easy to write when you bear no risk yourself. However, the situation between you and your construction partner is tense in such a way that the outcome can decide whether you go through the construction well and satisfied or not.

If it is clear that the colorful drawings you refer to were created individually for you and thus were an essential part of the consultation, you have a chance to achieve something or withdraw from the contract. If you do not know that, you can find out. If these images were not created specifically for you, the communication may have been clumsy, but a dispute over this would do more harm than good. This distinction is subtle but important.

In my opinion, by commissioning the additional costs for KfW40, you commissioned the change in wall thickness. But you certainly did not consent to a reduction of the living area.

That appears to be the case. The question is therefore whether consent to the change of the living area in relation to the “colorful drawings” would have been necessary. That determines whether it is an actual “reduction of the living area” or if the comparison between the living area on the colorful drawings and the contractually agreed drawing is even relevant.

From your point of view, you are right.

The general contractor of course sees it completely differently. He wants to save costs. Either to maximize profit or reduce losses.

Therefore, understandably, he kept the external dimensions the same.

A knave who thinks that something like this happens by accident.

Does the plot and the development plan allow the house to be enlarged?

In my opinion, by commissioning the additional costs due to KfW40, you commissioned the change in wall thickness. But in no way did you agree to a reduction of the living space.

You can register a cost reduction due to the reduction of the living space. The general contractor would (will) also claim additional costs due to the enlargement of the external dimensions. The dimensions were declared binding in the contract. But in my opinion, not the living area.

I am curious about the outcome.

Thank you for your contribution!

Yes, the plot and the development plan definitely allow that. That cannot be the issue.