owed soundproofing terraced house new build

So, we are one small step further, the sound insulation report is now available. The following facts are clear and undisputed for me after consultation with the lawyer, building expert, and study of the current case law:

1) Although it is a condominium-divided townhouse or apartment, the sound insulation requirements for a townhouse/semi-detached house must be met.
2) The requirements for increased sound insulation must be met. As an addition: Even the contractual clause "The company ### GmbH constructs the building measure according to sound insulation standard 4109. Increased sound insulation is expressly not agreed" is invalid and consequently, increased sound insulation was owed in this case.
3) Which exact sound insulation is owed must be determined based on the contract. This would typically be the appendix 2 of DIN 4109 or sound insulation levels II or III of VDI 4100 or DEGA recommendation 103 level A, that is something >= 67dB (airborne sound) and <=35-39 dB (impact sound).

Furthermore, the general contractor informed me (he probably is not allowed to, but the relationship between us is good) that he owes the developer the minimum standard according to DIN 4109 contractually and that this is fulfilled according to the sound insulation report by the facing shells. He also confirmed to me that increased sound insulation is not fulfilled by this. However, this concerns, and he is also correct, only the relationship between me and the developer. A joint appointment with the developer, general contractor, and us is scheduled for 25.04.

I would also be interested in the sound insulation certificate.
If it is available, you absolutely have to post it here (of course with addresses and names blacked out).

I have attached the certificate in blacked-out form. The image on page 11 is incorrect, please do not be confused by that. If further information is desired, please let me know. The report is a bit more extensive; I just did not want to upload 20 pages right away. I look forward to your assessments, I myself have to fight my way through a bit first.

I tried to read up a bit. There are some errors regarding the room sizes and volumes. However, I don't think that has much relevance. Three additional questions have arisen; perhaps someone would like to provide an assessment:

1) It seems to me that on the wall between our living-dining area and the living-dining area + hallway/stairs, only the partition wall between the two living areas is considered, and the stair area is completely neglected (the first two jpgs from the report). In my assessment, the partition wall between the hallway/stair area of the middle house and our kitchen-living area poses a significantly greater sound risk. The area of the partition component is also specified as 12.12 m², but the drywall lining and the partition wall to the neighbor are 14.86 m² (I have attached a section).
2) The values on the last two pages (Rw=997.7 dB and Lnw=3.0 dB) are absurd. Are these irrelevant for the case and therefore left as is, or did someone simply not notice their mistake?
3) Also, on the last two pages where the stairs are considered—ultimately all three cases are affected: In the stair area, should only the room height of the respective floor be taken into account, or rather the entire height of the stair area? Or does that perhaps have no impact at all?

So, we now had the potential clarification meeting with the developer, general contractor, and us. Who was not there: the developer. So the meeting was already obsolete again. At least we went over to the neighboring house. We rushed down the stairs and shouted a bit to get a first impression. It was somewhat better than feared but of course not as desired. After initial discussions with the lawyer and sound expert, studying various planning manuals, architect publications, technical articles, and judgments, I am sure that increased soundproofing is owed, whether according to DIN 4109 Supplement 2, VDI 4100 SSt II or III, DEGA recommendation, or whatever else—this could certainly still be disputed. This might become important later but is initially secondary, since none of it is fulfilled.

Whether the developer now realizes that the contractual requirements are not met and a solution together with our two neighbors should be sought, or whether he will fall back on the minimum requirements of the standard and want to contest it, we will have to wait and see.

Since other readers with similar questions might also come across this thread, I want to clarify two things again.

1) The thesis, vehemently held by some users here, that in a WEG-divided single-family terraced house (or apartment with terraced house character, vertical residential units, or whatever) the soundproofing requirements from multi-story apartment buildings must be met, is complete nonsense.
2) The minimum dimensions of DIN 4109 cannot be used as a measure because they only regulate the minimum requirements to avoid unreasonable disturbances. If a usual quality and comfort standard is owed (so no social housing, student dormitories, etc.), the required sound insulation level is higher. A soundproofing clause that aims at these minimum dimensions or explicitly excludes increased soundproofing is invalid according to § 307 of the Building Code.

I cannot yet present a result. But you can be sure that you will be able to read it here sometime.

It took a while, I have now received the measurement values. This is a rather heavily shortened report provided to me by the developer. Publication on the Internet is explicitly excluded, which is why I will refrain from doing so for now. Nevertheless, I would like to share the measured values with you.

Attached you will find the floor plan once again. My unit is located on the right. The floor plan is from the upper floor, the living room on the ground floor (the only adjacent room requiring protection) is marked in green for orientation.

The following values were measured:
Partition wall ground floor R'w (C; Ctr): 65 (-2;-5) dB
Partition wall upper floor Dn,w (C; Ctr): 65 (-2;-5) dB (partition area less than 10m²)

Staircase middle residential unit to our living room L'n,w (C1): 33 (-2) dB

Ceiling to our living room, ground floor bathroom is directly below upper floor bathroom and adjoins the technical room on our side.
From upper floor bathroom: L'n,w (C1): 40 (-1) dB
From ground floor bathroom: L'n,w (C1): 33 (-5) dB

I would appreciate an assessment. Hopefully, an appointment with the lawyer regarding the further procedure concerning the single-layer partition wall and the sound requirements will follow this week.

The technical problem was fundamentally botched and, in my view, cannot be remedied afterwards. The paneling with additional wall mass may theoretically help a bit, but in practice, [Globuli] are "highly effective" against it. I do not see anything achievable here beyond monetary compensation, and even there – you described at the beginning the problematic construct with a project GmbH as your legally actual contracting party – you probably have to be careful not to become a losing winner, i.e. in the end to have a ruling against an opponent who has then been liquidated. Take what you can get through conciliation, do not fatten the lawyers too much, and thank a saint of your choice that others have to endure more suffering.

Of course, it is not curable, financial compensation is the method of choice. I at least hope that the measures at the staircase had the desired effect and were not in vain. At least the measured result surprised me positively. The handover is scheduled for 31.08., after which I will be able to gain experience from real life.

If I am up to date, 2 of 15 residential units have not yet been sold, so there is at least still equity in the GmbH. Furthermore, I still have about €50,000 in outstanding payments after the handover. How to deal with this sensibly will certainly be answered by the lawyer. The risk of "losing winners" will be incorporated into the further decision-making process.