Additional costs / surcharge Higher windows

If your general contractor were to rip you off there, he would hardly do any less when calculating it out.

yes, but then he would make the windows pretty cheap. However, the surcharge for the higher windows can't be that high... or am I missing something?

Definitely do it!!! I can recommend making the windows as high as possible.

or am I missing something?

That I cannot follow your logic is a hint, but not a guarantee.

That I cannot follow your logic is an indication of that, but not a guarantee.

Ok, I will try to explain better. Windows up to a maximum of 2x2.25 are included in the flat house price. I am asking GÜ to calculate the windows separately, with the reasoning that I am considering doing EL (father-in-law is a window maker). Case A: GÜ makes only a small price difference to calculate separately. But this would imply that bigger windows from GÜ cannot be that much more expensive (based on your 5% calculation). Case B: GÜ makes a large (realistic?) price difference to calculate separately. This would probably then also result in a higher surcharge for bigger windows, and I could consider really doing EL, which I actually don't want, because of warranty (connections, tightness, etc.) or just living with somewhat smaller windows... One more question to the community here: If you had to decide: rather higher windows (1.635x2.325) or wider (2x2.25)?

Ah, now your error in thinking becomes clear: You assume the general contractor has logic or at least shame about contradicting himself; and you think he would "sell" you the same difference when adding as when subtracting. Sounds funny, you notice that yourself (?)

One more question to the community here:
If you had to choose: rather higher windows (1.635x2.325) or wider ones (2x2.25)?

As far as I remember, no one said you would have to increase the window area for the larger room volume – and I see no reason for that either. Don’t make the rooms higher without doing the same for the windows – that is, make the change neutral with regard to the lintel height (meaning the distance from the top edge of the window to the ceiling). I would choose this nearly "upper parapet height" between 30 and 35 cm.

Ah, now your error in thinking becomes clear: You assume that the general contractor has logic or at least shame about contradicting himself; and you think he would "sell" you the same difference when adding as when subtracting. Sounds funny, you notice yourself (?)

Well, but at least it is arguable. In a professional context (completely different industry and products) I was often able to achieve discounts in negotiations this way. So, for example, he calculates 5,000 EUR for 10 windows on the ground floor (which, in my assessment, would rather correspond to case A). Then he can hardly charge additional costs of 500 EUR per window for the 7 cm higher windows.

As far as I remember, no one said you would have to increase the window area for the larger room volume

No, no one did. That is rather my concern to ensure sufficient light incidence and whether I can compensate a lack of height with width. From your post I now conclude that the height has more optical reasons than reasons for lighting supply.