Building restrictions required a small coverage and hence the semi-basement was used for sleeping quarters.
The elevation to the street (north, road noise) was treated as a barrier and the house was arranged around a courtyard facing south.
The position of the house in the plot was chosen in order to create a smaller (decorative) garden on the front and a bigger garden on the back.
A gentle roof was chosen to allow for extra living space in the attic as well as heigh ceiling for the living room.