Dutch firm Wiel Arets Architects applied an intricate fritting technique to the glazed facade of this office complex in Zurich to give it the appearance of onyx marble (+ slideshow).

Located within a developing commercial zone outside the city centre, the 20-storey tower and five-storey annex were designed by Wiel Arets Architects to provide a new Swiss headquarters for financial services company Allianz.

Planning guidelines stipulate that all new buildings in the area must be clad in natural stone. But the architects chose to instead create the look of onyx marble to "allow the building to blend into its context while simultaneously maintaining its distinguished stance".

An abstracted pattern taken from the marble surfaces of Mies van der Rohe's Barcelona Pavilion was used to frit the glass. This was achieved by building up composite layers of black and white dots.

"The original image of the onyx marble was rasterised, and from this two versions of the same image were created - one black and the other white," project architect Felix Thies told Dezeen.

"These two images were then patterned and fritted on the back side of two different layers of glass, separated by a distance of six millimetres," he explained."When viewing the facade from an angle, the reflections of the rasterised patterns appear ever-changing, in accordance with the angle of the sun."

A regular grid of windows breaks up the facade and each one contains a silver curtain between two layers of glass. These are controlled by computer to vary the level of shade they provide, adapting to different weather and lighting conditions.

The building's entrance is at the base of the tower and leads through to a central staircase that ascends from the main lobby through all 20 storeys. This is to encourage employees to interact with people on different floors.

Four enclosed bridges connect the tower with the adjoining annex. There are also voids in the floorplates to create double-height spaces between storeys.

"The Allianz Headquarters can be experienced as horizontal and vertical landscape of neighbourhoods," said the design team in a statement.

Internal heating and ventilation is provided from behind a panelled ceiling system. These panels are made from steel and perforated with a pattern derived from Swiss chalet ornamentation.

A cafe and restaurant is located on the fifth floor, while the level below accommodates rooms for client meetings. Employees can also take time out from work on a roof terrace dotted with Japanese maple trees.

A three-level car park unites the two buildings at basement level and provides space for up to 300 vehicles.

Photography is by Jan Bitter.

Here's a project description from Wiel Arets Architects:

WAA complete construction on the Allianz Headquarters in Zurich

Allianz Headquarters is a 20-storey tower and 5-storey annex, the latter capped with roof gardens of Japanese maples; these two components are interlaced by four enormous bridges

The Allianz Headquarters is a hybrid-office and the pinnacle of a masterplanned mixed-use district on the edge of Zurich's city centre. Comprised of a 20-storey tower and a 5-storey annex, these two components are externally linked by a series of four bridges, and vertically linked by numerous interior voids and staircases; as such, the Allianz Headquarters can be experienced as horizontal and vertical landscape of neighbourhoods.

Fluidly connected to the city centre by a multitude of public transportation options, the building encourages the blossoming of twenty-first century office culture, which demands flexibility in space and its use, via its hyper-hybrid programming that amplifies 'interiority'.

The entire lobby and ground floor are publicly accessible, ensuring a continuous animation throughout both, which compliments the adjacent public square. A central staircase rises from the lobby up and into the 20-storey tower, allowing employees to, if desired, meander throughout all levels of the office without entering its core.

A café and restaurant are located on the fifth floor, rather than within the lobby, which creates a buffer zone between public and non-public areas. A 'business centre' is located one floor below, and contains meeting rooms for use with external clients. This 'business centre' enables employees to meet with their guests, without the need for elevators.

This new district's masterplan mandated that all building facades be composed of natural stone, yet it was chosen to frit this building's full glass facade with an abstracted pattern of Onyx marble - from Mies van der Rohe's Barcelona Pavilion - which allows the building to blend into its context while simultaneously maintaining its distinguished stance.

Each element of the facade contains a closed cavity system, in which an aluminium-coated silver curtain hangs, which fluctuates its degree of shading by responding to external environmental factors - a process administered by a computer controlled algorithm.

Interior heating and cooling occurs through a panelled ceiling system that utilises concrete core activation and concealed air ventilation. These 1.35 x 1.35 m panels are composed of 'crumpled' steel sheets into which a three-dimensional pattern, derived from traditional ornamentation of Swiss chalet eave, has been stamped, which introduces a larger scale to the interior office spaces by decreasing the amount of visible ceiling seams. Micro-perforations in the panels maintain ventilation, allowing for no visible interior air ducts and the placement of an acoustically absorbing sheet on the back of each.

Inhabitable volumes adorn the roof of the lower building, with several garden terraces for employees. These gardens contain a singular red Japanese maple tree, which return in the landscaping of the central courtyard below.

Both the 20-storey tower and 5-storey annex are adjoined underground by a tri-level 300 car parking garage, where most of the extensive IT and mechanical facilities are stored. Similar to a home, the Allianz Headquarters has been infused with espresso corners and lounge like spaces throughout, for instance, its four 8m wide bridges, to stimulate informal conversation within this highly formal working environment.