Soundproofing Assessment of 1965 Semi-Detached House

24 sand-lime bricks are the best thing that can happen to you in terms of sound!

That’s simply nonsense in general. It does nothing against impact sound; decoupling is the only thing that helps there. And I don’t see that here.

Unfortunately, you can’t see that in the architect’s plans.

To me, that looks like a classic single-layer partition wall, which was generally common back then – even ten years later still quite widespread in rows without depth (or height) offset.

However, I wouldn’t primarily worry about sound insulation: thermal insulation, heating technology, water pipes, and windows would be higher on my checklist.

Built around 1965 doesn’t automatically mean "old building," but it’s already in the yellow zone regarding underestimated effort for modernization.

Thank you very much in advance for the many infos.
Briefly about the house...
The gas heating was completely renewed 3 years ago
The windows are double glazed and made of plastic
The roof is about 10 years old
Water and electrical lines would be redone by us. Including new bathrooms.

But primarily it's about the noise level from the neighbor, whether and to what extent it can be heard given the circumstances.

But primarily it's about the noise environment from the neighbor, whether and how far it can be heard given the circumstances.

You won't notice each other's creaking bed, but you will more likely notice tantrums (including those with broken furniture for sure). You won't be woken up by the neighbor's toilet flushing. If he's not a drummer in a headbanger band, I would be relaxed about it.

... But primarily, it’s about the noise from the neighbor, whether and how far it can be heard given the circumstances.

You will always hear neighbors. Best through (closed) windows. When I’m outside in the front yard, I hear the neighbor’s discipline – mind you: single-family homes each with 3 meters distance to the boundary. I’ve heard that a basement blocks a lot. Element to check: the staircase. You will always hear piano playing, and moving cabinets is also highly likely. I lived in an end townhouse myself. If a neighbor’s cough bothers you, choose against a semi-detached or terraced house, because you have neighbors who make noises just like you do. Sound also easily carries noises and voices from house to house in a row.

The interior staircase is solidly made of concrete and clad with stone.
In addition, the house is completely basemented and has a [Bodenwanne].

We have another appointment with the seller next week. Maybe he can tell us something about sound insulation.

Can the house still have a separation joint that was simply completely over-clinkered so that it is no longer visible?
Is something like that possible, or does the separation joint always have to be visible?

Can the house still have an expansion joint that was simply completely overbricked so that you no longer see it?

I would rather believe in the stork. That would be a sound bridge and also prone to cracks. And very atypical.