Build a semi-detached house alone?

If the houses are properly decoupled, then you don't hear anything at all. Two separate house walls with an air gap in between, then there is 100% silence.

Yes, the air gap is important. Because: whether mortar lumps or insulation boards – any coupling of the two buildings "serves" as a transmission path. Regarding my suggestion with the WDVS system on this side of the house's exterior wall, that means staying at least 4 cm away from the boundary with the finished wall surface (plaster) (2 cm "finger gap" plus 2 cm disagreement in measuring the neighbor's half).

But DDH have no windows in between. Maybe two single-family houses with 6m distance and (open) windows are worse than two solid walls without windows. It's enough if the "noise neighbor" has the window open and the noise hits your own closed window.

That is of course possible, I can't judge. It certainly depends a lot on the structural conditions. For me, it would have been too risky in any case. Many years ago, I lived in a multi-family house where an identical building was adjacent, similar to a semi-detached house but over several floors, and the bathrooms next to each other were very sound-transmitting. You never have security against something like that, see our situation, and there have already been others here in the forum. I have also heard from various friends who live in semi-detached houses that they are very satisfied and don’t notice anything from next door. Or even have nice neighbors with whom you can have a pleasant chat. I don’t think you can say that in general.

I live in a semi-detached house and can luckily say that I hear 0.nothing from the neighbor.

We have small children, piano, drums, heavy metal, and no complaints from the neighbor.

During construction, you have to be painstakingly careful about that. A small lump of mortar can already ruin everything…

Yeah, here! We can hear structure-borne noise in our terraced house. Stomping, heavy things falling down, moving furniture (Why do people do that several times a day?). Everything still within limits and clearly more dampened compared to the apartment building but still not really great. Too bad, because we didn’t expect it that way. Airborne noise doesn’t come through here at all. Whether it was the classic mortar lump or construction debris or something else, we’ll probably never find out. But we’re not really upset, because a detached house wasn’t an option and with a semi-detached house that can happen too. I might build something with insulation and drywall in the living room, but will that help?

If I were to build a semi-detached house, I would build the entire house at once. At least then I can rent out the other plot and choose my neighbor. With us, the plots for semi-detached houses are exactly 50% the size of those for single-family houses. Instead of 900, for example, 450. Then you can just stay in the city and don't have to move to the suburb 15 km away.

If I were to build a semi-detached house, then I would build the entire house at once. At least I can rent out the other parcel and choose my neighbor. Here, the plots for semi-detached houses are exactly 50% the size of those for single-family houses. Instead of 900, for example, 450. Then you can also stay in the city and don't have to move to the suburb 15 km away.

That's absolute country bumpkin thinking again (no offense meant). In the truly sought-after/expensive areas, at least TWO semi-detached houses fit on 450 m². On 900 m², depending on the layout, there's a small apartment building with 6-8 units or 7-8 terraced houses. That way, you can also stay in the city ;) although a good part of Germany doesn't laugh out loud about that.