owed soundproofing terraced house new build

Repetition does not make it clearer either. I know what I bought, we are not at all in disagreement about that and indeed cannot be. The disagreement lies in whether the soundproofing requirements to be met in such a designed apartment are those of a terraced house or those of multi-storey residential buildings (so as not to hear the same paragraph from you again). I quoted you a ruling on this (can find more if needed) from which I formed my opinion. You say something different. Additionally, the developer now comes along and says he wants to build additional lining walls in front of the finished plastered walls with the further consequences that sockets have to be relocated, etc., and has also commissioned two expert reports, all just because he thinks: "Hey, this is a nice guy, we only owe him the 55 dB as fixed and finished construction, but now he is getting something extra even though we don't have to."

There is disagreement as to whether in an apartment designed in such a way (so as not to hear the same paragraph from you again) the sound insulation requirements of a terraced house or those of multi-storey residential buildings are to be met

But in that respect your judgment (or at least the quote from it) does not say much. Or can you say what "the technical structural appearance" is for the two variants?

It does not become any clearer through repetition. I know what I bought, we are not actually in disagreement about that and cannot be.

Additionally, the developer now comes along and says he wants to install additional facing shells in front of the finished plastered walls, with the further consequences that sockets have to be relocated, etc., and has also commissioned two expert appraisers, all just because he thinks: "Hey, this is a nice guy, we only owe him the 55 dB that are fixed and finished, but now he’s getting something extra even though we don’t have to."

The developer? Correct me if I’m wrong, a moment ago it was still the general contractor doing that. Who probably doesn't even know your purchase contract and you probably also don’t know his contractual relationship with the developer. It’s, for example, possible that the developer wants to guarantee you 55 dB according to his understanding, but has stricter obligations for the general contractor so that he can definitely deliver your 55 dB, because if not, it would be expensive for him...

Do you even have a basement? Or if there is a slab on grade, is it continuous?

And what is your actual goal? Is the sound insulation achievable without an additional facing wall definitely too poor for you? Do you want 67 dB come hell or high water? Do you want damages? Or what? I mean, your house is practically finished...?!

According to everything I have read so far, the sound insulation requirements for a terraced or semi-detached house apply to a terraced or semi-detached house, completely independent of whether it is a really divided plot or a WEG structure. I do not understand where you get the certainty that something else should apply.

…. Does not matter here.

the sound insulation requirements to be met are those of a terraced house or those of multi-storey residential buildings.

Residential building. These are apartments, not terraced houses.

I quoted a ruling for you

..which refers to terraced houses, but not to residential buildings. The ruling does not apply to you or your purchased apartment.

It may be, for example, that the BT wants to guarantee you 55 dB according to his understanding, but the GU is more strictly obligated so that he can definitely provide you with your 55 dB

It could be, but I consider it very, very unlikely in this construction project. The developer doesn’t have much knowledge about the construction project and relies here on his architect and the GU.

Do you actually have a basement? Or with a slab on grade, is it continuous?

No basement, continuous slab on grade.

And what is actually your goal? Is the sound insulation achievable without a false wall definitely too poor for you? Do you want 67 dB at all costs? Do you want damages? Or what?

That’s a good question. First of all, I want to go into the next meeting as well informed as possible. At the moment, I neither know the expert reports nor have I been able to test the sound insulation yet. I’m moving from an old building from 1900 into a (perceived) terraced house; perhaps it is completely sufficient for me. The GU told me that he wanted to build double-shell and this was planned in the first drafts, but later was redesigned (before purchase). If this redesign is again based on faulty calculations, then I would also like to receive compensation (damages) for it. What I don’t want is a false shell being built that barely has any effect. However, I will only be able to assess that from the expert reports as soon as I have them.

which refers to terraced houses

No, to divided residential property like mine.

No, on shared residential property like mine.

You read what you want to read and compare apples with oranges... You bought:

Apartment (with townhouse character)

and not a townhouse.

It is a WEG shared townhouse with corresponding separate ownership of the house and land.

…

In this respect, it does not matter whether it is legally townhouses on separate land or apartment ownership on undivided land. The decisive factor is the technical appearance of the object.

This is not about the problem of building houses on undivided land, because that also exists. What you bought is an apartment. Technically (apparently for us according to your explanations) an apartment, optical character like a townhouse.