In a densely developed district of Hamburg, a two-storey building dating from the 1950s has been raised in height by a further two floors, increasing the living area in the block by 175m2. The additional loads are transmitted via the party walls at the sides and via the central staircase core. This allowed a flexible layout with dwellings extending over the full 7.50-metre depth of the building without intermediate structural walls. The layout can easily be divided into one, two or three units. The striking feature of this new development is the street facade with its concave-convex, translucent, hollow-core perspex slabs. These were bent to shape on site and form a visual link between the upper levels. Depending on the incidence of light and the angle of view, the coloration of the facade changes, lending the building a quality of lightness. The curved elements form the outer skin of a ventilated facade, the inner layer consisting of fixed -glazing with translucent thermal insulation. In this way, it was possible to achieve an open and economical form of construction.