Leading the way in high-rise construction. The Hohlstrasse office tower in Zürich’s up-and-coming Altstetten suburb had to comply with new high-rise building regulations governing aesthetics and landscaping issued by the city authorities at the start of the planning process. In addition, the building was to set new standards in terms of both energy consumption and room climate control.

Sited over a rail freight station, adjacent to residential developments and service buildings, and surrounded by a small park, the tower makes a clear statement in a multi-layered district with generous openings signalling its gateway status.  

Aptly named, the Obsidian building is both striking and elegant

The complex is divided into two parts, one rising 15 floors, the other, set back at an angle, just six. A dark, monolithic block broken up only by the discreet joints between its exterior windows, it is slender in relation to its height of almost 60m. A ground floor featuring a café, seminar rooms and exhibition space provides the base for the flexible office space with far-reaching views which rises above it.

The double façade provides energy efficiency, sound insulation and pleasant light and climate conditions. The outer grid of panels creates a temperature-controlled air exchange that helps achieve optimum energy consumption, while the transparent surfaces mean that windows can be opened to allow individual room climate control. The double-skinned façade design also obviates the need for anti-glare measures.

Versatile space, generous feel

Functional neutrality and the option of flexible expansion are integral to the design concept. 1.45m inside the exterior façade sits a sliding wall which conceals the building’s technical plant. Thanks to the separation of building services and functional space, the technical services will continue to function if the wall is moved. Alongside the high-ceilings, few load-bearing structures and unhindered views, an excellent gross- to net-floor-area ratio creates a spacious feel. The interior is characterised by the contrasting use of light and dark tones.