A single-family house on a slope is extended by a residential unit through maximum lengthwise expansion. Both inside and outside, new and old remain distinguishable, but the interface is blurred by spatial overlaps. The focal point of the new apartment is the extra high living space, which brings the existing gable facade into the interior. In the tradition of Loos, a series of rooms with different characters are integrated into the simple, iconographic building volumetry. Two connecting elements hold old and new together like a bracket: On the north side, the roof opens for a continuous window strip; in the south, a loggia extends along the entire length of the building. It interferes with the semantics of the existing building and reinterprets what already exists. The annexe is constructed as a self-supporting timber structure. The walls and ceilings are prefabricated and placed into the in-situ concrete shell. The concrete shell gives the building its distinctive expression. The concrete has a stony appearance due to the admixture of crushed Jura gravel and white cement. Without any colour pigmentation, a light, warm and natural shade is thus achieved. In addition to the smooth surfaces showing the formwork pattern, some parts are sandblasted. The subtle interplay of different surface textures makes familiar motifs appear or disappear, depending on the light.