Semi-detached house with 105 sqm living area and 80 sqm usable area

Presumably a standard 7x10m floor plan: 60 m2 on the ground floor, 45 m2 in the attic due to the sloping ceilings for 3 bedrooms with bathroom plus 1 "office" of 8 m2 on the ground floor plus living room on the ground floor. That makes 5 rooms with initially 105 m2 of living space.

The technical room is in the basement instead of the "office" on the ground floor as in semi-detached houses without basements; of course, the basement has 60 m2 like the ground floor, due to the state building regulations (height, light wells, escape route) counted as usable space, and in addition, there are 20 m2 in the attic, mostly as space between 1 and 2 m clear height – the attic may also be referred to as "studio," "extension reserve," or similar, and then represents the fifth room, which would not be entirely correct if this space elsewhere would only be counted as usable space – because often it lacks the second escape route and ceiling height.

PS: Id of the listing on Immoscout (or similar)?

Why not. For a family with several children and less money. Or if someone has two children and needs an office. That’s enough. When the children are outside, you have a guest room and still no big empty house.