First of all, thanks to Doc.Schnaggls. That is exactly the right description if you have no idea about all that stuff.
Since I am located near Ulm, most likely the State Building Code of Baden-Württemberg applies. It states:
"Full stories are stories that protrude more than 1.4 m above the average measured ground surface and are at least 2.3 m high, measured from the top edge of the floor to the top edge of the floor of the story above or to the top edge of the roof covering of the roof above. The average measured ground surface is derived from the arithmetic mean of the elevation of the ground surface at the corners of the building. Not considered full stories are 1. stories that are exclusively used for housing building services and heating systems, 2. top stories where the height of 2.3 m is present over less than three quarters of the floor area of the story below. Cavities between the top ceiling and the roof, whose clear height is less than required for living spaces according to § 34 Abs. 1, as well as open galleries up to a floor area of 20 m² are disregarded."
Does that mean that everything above a knee wall of 1.40 m would be another full story? Not below, right? Then it would be a single-story building with a ground floor and upper floor with a knee wall of 1.40 m?