Reduction of living space due to knee wall height

Regardless of the reasons, this reduction saves stones and must be compensated.

That sounds like a discount – but in essence, I see it rather as damages (and also the possibility for the builder to reject this change of the contractual basis).

If I order a new car, the dealer cannot just have it lowered, even if he does not charge extra for the lowering: there could be speed bumps in my residential area, or I could have "back problems." Then that is a defect in the goods for me.

And it is simply in the nature of a knee wall that one can rightly expect it to fully substitute a knee wall. Behind a normal knee wall, you would have at least a usable recess. Having to setback about 40 cm with a front wall unfortunately does not create usable space behind it. Or placing a bed correspondingly far from the wall: then the passage to the wardrobe becomes narrower. These are not issues for “oops, oh, I completely forgot to tell you,” is this bad? – yes, it is!

The 30cm would be a reason for me to cancel the contract and completely replan.