Prefabricated house, poor sound insulation

Where do you get your knowledge about the defects? Did I overlook that?

There is nothing about installation defects ...

With mine, I wanted to point out that (especially in prefab house construction) not only a component that is acoustically incorrectly designed/chosen can be the cause, but also the defect/incorrect installation. And usually, no one can find that out by datasheet remote diagnosis or as a layman by putting an ear on it.

Now he is replacing windows with higher SSK.

He is not replacing the window, but the glass. The acoustic quality of the frame and sash frame, the seal between the frame sash and the sash frame, and the connection quality of the frame to the wall component remain the same as in the existing situation.

I only know about bricks and there the manufacturers specify the sound insulation value. So I can check whether a 70 dB noise will be reduced to the specified 40 dB or not?

This is about a prefab house. Here, the execution quality is crucial for sound insulation; the acoustic performance figures of the components are rather secondary.

That is cheaper than a report against pointless DIN values

You have already named €800 for a measurement. What do new windows currently cost, say SSKIII or just the corresponding glass? I don’t have prices available anymore.

800 euros was unfortunately ONLY for measuring ... and then the statement: xdB ... everything else like looking at documents or setup I estimate will cost significantly more but you should be able to assess that better?

And maybe the OP can tell us what a new disc costs .... I also estimate about 800.

I guess so

Before we start treating layman-"estimates" as gospel here, we should soberly look at the facts.

Unfortunately, 800 Euro was ONLY measuring

The expensive part of a measurement job is not the measurement technician or the travel. By far the most expensive is the usage of the measuring device.

it will cost significantly more but you should be able to estimate that better, right?

I don’t have to estimate at all. A look into the Siegburg tables says, with an extremely generous assumption per building physicist, 100€/h. Not a few probably do it for 75€/h.
Review of the documentation, plans, and documents: half a day, calculated generously. If he looks at everything again on site: another half day. So another 800€, probably less when calculated with hourly rates. If you agree on a flat rate, he might even work faster and cheaper. For that, you get a statement about the cause that will hold up at least until a possible court trial.
I would have no interest in a try and error guesswork, especially not considering the financial and legal consequences that such an intervention in a building still under warranty entails.

One can figure out a lot by using common sense, experimenting, and testing oneself. Blanket accusations of processing defects are not very constructive. First, focus on the facts and check what the structure is actually supposed to deliver; if it already becomes apparent that the glass is, as almost always, the weak point, then a replacement can only bring a significant improvement. If one is still dissatisfied, an expert can be called in. About the expert just this much: he who measures measures nonsense! Caution is advised here.

Blanket accusations of workmanship defects are not very constructive.

No one is making blanket accusations of workmanship defects. The fact is, however, that workmanship defects in prefabricated houses have a more critical impact on the overall acoustic system than workmanship defects in solid construction.

Glass is almost always the weak point

Which brings us back to generalizations. Sure, glass is a part of the overall window system. Of course, also the largest in terms of surface area. But the frame and sash are also part of it, as well as seals and connections to the exterior component. Just the impact on flanking transmission caused by typical installation errors... mineral wool strips inserted only on the room side, leaking joints, incorrect foaming around mounting blocks, no backer rod, glass with leaked SF6... The elephant can surely share anecdotes about this.

Anyway, the original poster acted and I hope it brings relief. Maybe he will report back in due time.

Nobody generally accuses of processing defects. However, the fact is that processing defects in lightweight construction have a more critical impact on the overall system in terms of sound insulation than processing defects in solid construction.

Which brings us back to generalizing. Of course, glass is a part of the overall window system. Naturally, it also accounts for the largest area. But the frame and sash frame are also part of it, as well as seals and connections to the external component. Just the flanking noise caused by typical installation errors... mineral wool strip, which is only applied on the room side, leaky joints, incorrect foaming at mounting blocks, no backer rod, glass from which the SF6 has escaped... The elephant can certainly share anecdotes about that.

Anyway, the OP has taken action and I hope it brings relief. Maybe he will report back in due course.

Then a concrete question:
And the fact that the noise comes in through the frame, you should be able to hear that yourself, right? Put a stethoscope on it and test whether it comes through the glass or the frame?

Because either the installation is massively wrong, the effect then is too, or it is not that bad, then it cannot be installed incorrectly either, or am I misunderstanding something.
Also, a blower door test should have revealed that already, no idea if the OP had one done, for example KfW etc.