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

I want to stand up for the "victim" here. I also don’t understand why he should be to blame. He goes to the general contractor, wants a KFW40 house, and it should be that big with that much living space. The sketch creator obviously slipped up. That can happen. But at the latest, the proper draftsman should have gotten suspicious and clarified it with the customer. Something like "unfortunately, this is not feasible, but we have the following options." Throwing him the finished plan without any comments is not very classy, in my opinion.

Could you please clarify that? Why is this my fault? I communicated to the general contractor from the beginning what I wanted, right? Upon which he created this colorful sketch with corresponding areas expressed in numbers in the middle of the rooms. I don’t understand, sorry. I’m not a professional.

Not only are you not a professional, but the draftsperson isn’t either. That’s why the conflict between sand-lime brick and EH40 in the colorful sketch may not have been noticed yet. With a structural wall shell made of sand-lime brick caliber 175, a U-value for EH40 is simply not achievable. So the draftsperson must have switched to sand-lime brick caliber 240, and the total wall thickness accordingly increased. You can easily use sand-lime brick for the interior walls and mix it with aerated concrete for the exterior walls; then this increase in total wall thickness can be reversed. Viebrockhaus builds EH40 as standard, with 44 cm total wall thickness including a 15 cm thick structural wall shell made of aerated concrete. However, that would be a non-systematic total wall thickness, whereby the difference to the octameter grid should be properly compensated on the inside. You can mention the exact wall construction that was planned before the change.

I want to jump to the “victim’s” defense here. I also don’t understand why he’s supposed to be at fault. He goes to the general contractor, wants a KWF40 house and it should be that big with that much living space. So the sketch creator screwed up. That can happen.

The OP is not the "victim," but the cause of the easily fixable little problem. You can’t just swap a brick with a terrible U-value without consequences (which a draftsperson usually doesn’t oversee).

But at the latest, the right draftsman should have been suspicious and clarified that with the client. Something like “unfortunately not feasible like this, but here are the options…”. Throwing him the finished plan without comments is, in my opinion, not very polite.

As the OP has meanwhile admitted (in post #16), it wasn’t even thrown in his face like that.

Ultimately, it is now as it is, and we best assume that neither side intended anything dubious or even malicious; often it is a mixture of things or mutual expectations of the other. As long as the GU is reliable, the TE already has an advantage that not all builders are granted, and this issue will surely be resolved in discussion. I have experienced GUs who were not quite so proficient with the topic of Kfw; mine was even an energy consultant as well, but he threw in the towel with Kfw40 because his software couldn’t handle it. Fortunately, I then found a really competent energy consultant quite far away; these are actually also quite rare. What rather arises for me is the question of whether the current or now corrected floor plan is actually to be built as such, so that the discussion should only be about this "misunderstanding" issue. If the TE would also like to discuss the floor plan, he should start here from scratch with the questionnaire as well as the plans. As it is now, one would otherwise always have to piece everything together from the thread. I find the Kfw40 insulation standard, which I prefer, good regardless of how it is achieved, since something will be added on both sides anyway.

The OP is not the "victim", but the cause of the easily fixable little problem. You cannot just replace a stone with a miserable U-value without consequences (which a draftsman usually does not oversee).

That's nonsense. If 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 written in the contract. What exactly are you buying? If the house with x square meters of living space is stated there, then the general contractor cannot just reduce it.

Not only are you not a professional, but the draftsman isn't either. Therefore, the conflict between sand-lime brick and EH40 in the colorful sketch may not have been noticed yet. With a construction masonry shell made of sand-lime brick size 175, a U-value for EH40 is simply not achievable. So the draftsman must have gone for sand-lime brick size 240, and the total wall thickness has accordingly swollen.

I think you misunderstood something here. From the beginning, a KfW 40 house was planned. For that, I specified sand-lime brick 17.5 + insulation + 11.5 clinker. As it now turns out (last email from the general contractor), an insulation thickness of 13.5 was assumed for the sketch. This insulation was now planned to be 6.5 cm thicker, which led to the still 17.5 sand-lime brick wall being shifted inward. I hope I have now made this a bit clearer. Does this possibly change your opinion?

What exactly are you buying? If it says house with x square meters of living space, then the general contractor cannot simply reduce that.

As a rule, it is much more critical to exceed the framework of the previously planned exterior dimensions. A floor plan where rooms no longer work if they are 6.5 cm narrower would be a planning error.

I think you misunderstood something here. From the beginning, a KfW 40 house was planned. For this, I specified sand-lime brick 17.5 + insulation + 11.5 clinker. As it has now turned out (last email from the general contractor), an insulation width of 13.5 was assumed for the sketch. This insulation is now planned to be 6.5 cm thicker, which caused the still 17.5 sand-lime brick wall to be shifted inward. I hope I have now made this somewhat clearer. Does this perhaps change your opinion?

Assuming a gap of 13.5 cm is system-compliant and would usually be planned for 12 cm insulation thickness plus a finger gap. The standard of the general contractor probably assumes a construction masonry shell made of porous brick or aerated concrete. Since sand-lime brick has a significantly worse U-value and the 12 cm insulation thickness offers limited potential to compensate for this through a more efficient insulation material, a problem arises (which only becomes evident in the heat demand calculation). So one of the individual thicknesses must be dimensioned higher here – done here absolutely professionally by sizing the intermediate space to 20 cm, which here is just exactly a quantum leap. I already understood you correctly, and my opinion therefore remains unchanged: move away from sand-lime brick here, use aerated concrete instead, that should already solve the U-value problem here. Sand-lime brick has only one disadvantage for you here. If you want the advantage (in sound insulation value): that practically only applies to the interior walls, which remain unaffected by the material for the exterior walls. But an attentive reader who has been following along "for some time" should already be able to sing along everything I have written in this thread today by heart, these are evergreens here.