Built-in windows do not match the window plan. Objection?

To me, it looks like the shell builders made a mistake with your 8 cm

I would have thought so too, but:

Now it is the case that the shell openings correspond to the floor plan in reality.

Besides, one would have noticed it before installing the windows (because you do measure afterwards ). So: Are you sure the shell construction is correct?

I would have thought so too, but:

Besides, you would have noticed it before installing the window (because you do measure afterwards ).

So: Are you sure the shell construction is correct?

I do not doubt that the shell construction measurements are correct. If that were the case, the OP would surely have mentioned something about it.

I assume that the window opening was left out in the wrong place (measured -8 cm from side x).


Construction expert on the go

That the raw construction measurement is correct, I do not doubt at all. [...] I assume that the window opening was left out in the wrong place [...]

That is a contradiction to me.

A defect would only be one _after_ acceptance of the construction; so far it is a simple error that needs to be corrected.

1.
Botched construction remains botched construction – and thus a "defect". Before and after acceptance.

Acceptance is merely the point in time when the legal nature of a claim due to "defects" changes from the so-called obligation to perform into a warranty obligation.
In other words: With serious defects before acceptance, as a contractor I may not yet have "performed"; after acceptance, it is a warranty claim (for which the burden of proof reverses after acceptance).

2.
The first question here is whether extensive subsequent performance can also be demanded for (visual) defects – or whether that would be disproportionate:

§ 635 III Building Code
The contractor may refuse subsequent performance without prejudice to § 275 (2) and (3) if it is only possible with disproportionate costs.

Meaning:
If a contractor refuses to remedy the defect due to disproportionately high effort (§ 635 (3) Building Code), they are still liable to the client for damages because of the defect.
However, the client cannot then claim the costs of defect remediation as damages, but only the reduction in value of the construction. To avoid contradiction, case law holds that damages cannot be claimed in the amount of the defect remediation costs when those costs are disproportionately high (because they would also be disproportionately high!). Rather, in this case, the client can only calculate their damage based on the reduction in market value.

3.

I assume that the window opening was left at the wrong place (-8 cm from side x measured)

If that is the case, then it is not a planning error but an execution error.
Then it is not just a visual defect, but actually affects the dimensions: One wall panel is 8 cm too long, the other side 8 cm too short. For example, do the 82 cm that are drawn as wall width in the corner in the first drawing on the upper floor correspond? Or was the lower window on the ground floor shifted to the right? There are no dimensions there.
Anyway, that is not how the OP created it; the drawings show congruent line alignments.
Is there a clause in the contract about the priority or binding nature of drawings?

4.
Central question therefore: Is subsequent performance disproportionate?
It depends....

If the overall weighing of interests shows that the appearance is of secondary importance and the defect does not lead to any functional impairment, the contractor can refuse subsequent performance more easily than if the client's interest is also directed at a visually flawless service. This would be the case, for example, with high-priced works or special mention in the contract. For example, in the purchase of a new car, a slight deviation in the shade of color was already considered a defect.

That is a contradiction to me.

The opening in the masonry for the window is correct; the element 2.26 x 2.135 m can be installed.

According to the manually created attachment, the green window reflects the planning, the red window the actual condition.



Construction expert on the go

The casus knactus is surely that the wall openings were known and were probably made correctly


and



What was not known and was probably only determined by the window manufacturer or whoever ???? is the width of the corner support. In the remaining ground floor section, the window was then split again. However, the center point of the two doors shifted further to the right according to the plan (downwards to the left in the view), due to the widening of the corner support, resulting in this outcome.


So in my opinion, what was missing was the correct calculation of the corner support and THEN the exact planning of the window opening positions.

The question here would be who could have calculated the corner support when and whose responsibility it would have been. Based on the drawings, I would say that something additional would have had to be agreed upon, because the drawing explicitly states that the corner support is to be calculated according to the structural analysis. So it could be wider or narrower than drawn.