Experiences from a friend's mid-terrace house: Inside, you hear nothing from the neighbors. Absolutely nothing. On the terrace, it’s a different story – you hear every word of the neighbors, which is especially great when the neighbor is very esoterically inclined or a bit crazy.
With the newly built semi-detached houses here, it will probably be similar: from the masonry, each half is a house on its own. Because the plots are tiny, the terraces are stacked on top of each other. The adjacent single-family house has its terrace directly next to it (and 1m higher) – this will be a front-row seat for upcoming family and marriage quarrels, as long as they take place on the terraces of the semi-detached house.
Therefore: whether it’s a single-family house on a small plot with a terrace adjoining the next property, or a semi-detached house – in the end, it probably makes no difference. Anyone used to the balcony of an apartment building with eavesdroppers above, below, left, and right will have no problem with this.
(Should I tell our quarrelsome retired neighbor that when I’m having breakfast with the window tilted, I hear every word of the arguments and shouting in their living room when they’re airing out? [ER ist schwerhörig, deswegen ist SIE umso lauter ])