Telefonzentrale Wollishofen

Inner Densification through Adaptive Reusse

The telephone exchange in Wollishofen was built in 1938 by the former PTT and extended several times over the following decades. In 1952 a two-story annex was added on the south side, in 1965 an additional floor with a pitched roof. After the sale by Swisscom in 2010, the building underwent a complete renovation until the end of 2012, including the addition of a new attic floor.

The property remains one of the key telecommunication centers in the Zurich area. At the same time, the earlier extensions contravene current building and zoning regulations: setback rules, building height, and utilization are exceeded. Nevertheless, due to grandfathering, another upward extension was approved, as the permissible number of stories had not yet been exhausted.

With technological advances in telecommunications, the demand for space was significantly reduced. Operations are now concentrated in the basement and ground floor, freeing the upper floors for new uses. The project envisioned their conversion into apartments, complemented by a penthouse with generous terraces. The interior layout was designed deliberately neutral, with technical installations compactly integrated, ensuring that future changes could be carried out with minimal effort. An elevator was installed in the existing stairwell to provide barrier-free access. Cellars and technical rooms are in the basement, where the new building services center was integrated into the former tank room.

With over 650 square meters of additional living space, new housing was created in a well-connected location, without the need for additional land or infrastructure. The project exemplifies inner densification, realized not only through large housing estates but also through smaller, continuous conversions and extensions. The telephone exchange thus becomes a symbol of building onward from the existing substance.

The façades respond to the new use yet remain restrained. On the first floor, window openings were enlarged within the reveals, producing a calm and unified appearance. Two balconies were added to the street façade on Kalchbuehlstrasse. The volume was refurbished and painted in ivory tones, the windows contrasting in dark aubergine. A continuous railing concludes the building above.

The upper floors are characterized by column-free open spaces, structured by room-defining brackets. These incorporate all infrastructure such as kitchens, bathrooms, and storage rooms. Rooms are organized along the longitudinal façades, creating a classical enfilade. Large swing doors allow the sequences of spaces to be flexibly opened or closed. The color and material concept is oriented towards the human scale: color accents structure depth, while the base tone lends warmth to the generous volumes.

The attic was added as a prefabricated element construction. A stud framework forms the basis, clad with panels that partly act structurally. Doors, lights, and switches are integrated. Large-format glazing replaces plaster along the façade line, giving the attic a light yet compact appearance. Recessed parts are clad with ventilated fiber cement panels. Birch plywood characterizes the interior surfaces, while the floors are finished in anhydrite.

Through the adaptive reuse of the upper floors and the upward extension, the telephone exchange in Wollishofen has been given a new function and identity. The historic volume is respectfully continued, the existing substance preserved and complemented by precise interventions. The building thus remains a distinctive element of the neighborhood, while at the same time re-emerging in new brilliance as housing prepared for the future.

Client: Kalchbühl Raum AG

Planning: Rossetti+Wyss Architekten, Urech Bärtschi Maurer AG, Zürcher Elektroplanungen AG, KWP Energieplan AG, Bünder Sanitärplanung AG, Bakus Bauphysik & Akustik GmbH

Photos: © Jürg Zimmermann