Rising 80 meters from the ground, this 26-storey apartment block on Zürich’s Freihofstrasse creates a striking new architectural landmark between Hardstrasse and Altstetten station. The newbuild stands on the site of a former garage, making a link between the area’s industrial past and contemporary, resource-efficient architecture. The conversion of an existing shed into a loggia-style covered terrace and the location of commercial units on the ground floor help bring new life into the neighborhood. On the first floor, communal rooms, workshops and green spaces promote encounter and exchange between residents. The 23 floors above offer a wide variety of apartment configurations.

Integrating the old shed into the new building demanded a number of complex design solutions. Most of the original complex’s load-bearing structure has been retained with just four sheds giving way to the new high-rise, which is decoupled from the retained shed structure by a movement joint. Horizontal extensions and connections provide functional links between the old and new structures. A terrace slab doubles up as a structural building plate to maintain the dimensional stability of the shed construction.

The block’s load-bearing structure is based on an optimized concrete frame construction with slim beam floors, prefabricated columns and a circulation core for horizontal stability. All other interior walls are self-supporting. The lightweight construction method was chosen to ensure an efficient construction process and a certain degree of flexibility. At just 14 centimeters thick, the in-situ cast concrete slabs sit on prefabricated longitudinal concrete beams that transfer the structural loads to prefabricated concrete columns. The building’s floor plan, almost biaxially symmetrical, has a central circulation core that provides efficient bracing against horizontal wind and earthquake forces. Walls and columns are dimensioned according to load from top to bottom with increments matching apartment types. The two in-situ cast concrete basement levels form a rigid box that clamps the building shaft in place and transfers loads down to the foundations, which comprise large-caliber in-situ cast bored concrete piles.

This truly interdisciplinary project is characterized as much by its high degree of prefabrication in structure and fit-out and its strict policy of system separation as it is by the economy of its building services technology and kitchen and bathroom fit-out design: a strategy that improves build quality and simplifies adaptations later in the building’s lifecycle as well as reducing material usage.