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Precise Schweiz: Mixed Development in Zurich by Caruso St John Architects and Bosshard Vaquer Architekten

A new piece of city is gradually coalescing around Caruso St Johnʼs thoughtful and precisely crafted mixed-use scheme in Zurich

From the first competition entries that they undertook together in the early 1990s, the London-based architects, Adam Caruso and Peter St John, have maintained a long engagement with the question of how tectonic expression can be directed to the cultivation of urban atmosphere. Eschewing the current Modernist lingua franca of floor-to-ceiling flush glazing, they have consistently sought to make facades characterised by a powerful material presence and intricate surface handling. The commercial architecture of the great metropolises of the late 19th and early 20th centuries has served as a particular source of inspiration in that quest. The terracotta facades of Hendrik Berlage’s Holland House in London (1916) informed the use of the same material as the cladding of the New Art Gallery in Walsall (2000). At the time of designing his building, Berlage had recently returned from a visit to Chicago and the influence of Louis Sullivan’s repetitive but richly modelled facades is much in evidence in the London project. Sullivan was a still more direct inspiration for Nottingham Contemporary (2009), a building faced in a curtain of precast-concrete elements ornamented by an inscribed lace pattern. The tectonic culture to which all of these projects belong can be traced back to the argument presented by the German architect/theorist Gottfried Semper in his book, The Four Elements of Architecture (1851), that the facade’s origins lie in the art of weaving.  In each instance, the elevation presents a pointed ambiguity: at once exulting in the substantial character of its component parts while striving for a fabric-like delicacy.

Caruso St John’s pursuit of surface richness represents an attempt to redirect contemporary architecture away from the exaggerated formal dynamism that has become its focus in recent decades. There is a strong urban agenda at work in that choice.  In place of the production of singular objects of ever-more dramatic shape, the practice sees its fundamental responsibility as providing the streets and squares of the city with definition and character. The massing of its buildings tends towards the laconic, the arrangement of their windows towards a considered neutrality. The scope for invention is defined by the city’s demand for a generality of expression. Given these interests, it is a source of frustration that the practice has not secured opportunities to work on projects of real urban consequence sooner. The two galleries mentioned are substantial and highly accomplished buildings but characteristic of a workload that has long been dominated by the design of art spaces. It is only in the last few years that the firm has begun to secure large-scale commissions for the background material of the city: offices, retail and housing.So it is particularly welcome that the first built output of this new phase in its development has all three of these uses in a single structure. Undertaken in collaboration with the Swiss firm, Bosshard Vaquer, the project forms part of Europaallee, a major redevelopment of land owned by the Swiss Federal Railways (SBB) that lies alongside Zurich’s principal station. Representing a 500-metre-long strip sandwiched between train tracks to the north and a parallel (and historically rather down-at-heel) road to the south, the land is being transformed in accordance with a masterplan by Kees Christiaanse. That scheme productively complicates the site’s linear configuration by cutting a diagonal pedestrian route across it: a street that connects the station (in the north-east corner) to a new square midway down its length. From here an existing road cuts deep into south Zurich, giving the square the status of a gateway to the station.

Siteplan

Site plan

Among the buildings planned to address this space, Caruso St John’s is the first to be completed. The diagonal route extends along its northern frontage framing a volume of broadly triangular footprint. A number of entrants to the 2007 competition for the project proposed building to a constant height across the entirety of the plot, while others divided the accommodation between a base and tower. The winning scheme was alone in advocating the use of a base and two towers − an arrangement that offered a more animated counterpoint to the unfortunately lumpen blocks that have been realised to the immediate east. For all that strategy’s scenographic appeal, achieving a viable configuration did not prove easy. Tall buildings in Zurich are subject to legislation that forbids them to cast a shadow on a residential window for more than two hours a day. Both of the scheme’s towers contain apartments and ensuring that one did not overshadow the other for more than the permitted time was particularly challenging given their proximity. The proposal also ran counter to a number of the masterplan’s expectations. Providing the towers with a sufficiently vertical expression necessitated the base being set significantly lower than the other buildings on the street. Christiaanse acknowledged the merits of that discrepancy but was not persuaded by the architect’s argument that the towers should be of equal height. Concerned that all buildings ranged around the square should step up as they approach it, he insisted that the west tower be set two storeys higher than the east.

In Caruso St John’s home country, the distribution of apartments above office space is all but unknown, as British housing is ordinarily built for sale, effectively prohibiting a site’s future redevelopment. Here, however, SBB has kept ownership of the whole building with all apartments being made available for rent. In devising a facade treatment for this hybrid typology, the architect has resisted any temptation to dramatise the distinction between the parts.

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In place of the production of singular objects of ever-more dramatic shape, the practice sees its fundamental responsibility as providing the streets and squares of the city with definition and character

The principal means by which the facades are organised is a grid of precast-concrete elements, that diminish in size from bottom to top. The treatment serves to exaggerate the towers’ height while introducing a greater delicacy as the facades rise. The device was a feature of the competition scheme but in the course of the project’s subsequent development the facades came to present a significantly less austere image than was suggested by the initial renderings. 

The impulse for a livelier expression came from the client who had been chastened by the hostile public reaction to earlier phases of the development, notably a singularly joyless teacher training college by Max Dudler. Having recently begun to explore the role of ornament in projects like Nottingham Contemporary (AR January 2010), Caruso St John was by no means resistant to that prompting and set about developing a revised treatment that incorporated polychromy and other surface effects more commonly associated with an architecture made in natural stone.  Where the towers had originally been envisaged with flat roofs they also acquired highly characterful profiles faced in copper − a change that served to hide technical equipment and to allow the penthouse apartments projecting skylights. The work of the early-20th-century Zurich architects Otto and Werner Pfister was a crucial guide in this process of elaboration.

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Floor plans - click to expand

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Part plan, section and elevation - click to expand

Prior to tender, the facades were detailed so that the exceptionally large concrete elements wrapping the five-storey base might be load-bearing while the ones above would be hung. In an (ultimately fruitless) attempt to reduce construction time, the contractor insisted on hanging the base cladding too but the change was undertaken without visible consequence for the design.  So the impression remains that of an assembly of massive piers and beams, articulated by wide recessed joints at their meeting. The parts are further distinguished by the contrast between the smooth finish of the vertical elements and the deeply pitted texture of the horizontals. London’s post-war Barbican development achieved a similar finish by bush-hammering vast areas of wall after casting. Here, a more mechanised process has been employed: a single length of concrete was cast and worked by hand, enabling a silicone mould to be struck which was then used for the fabrication of every element in the building.

The mixed programme required the articulation of an unusually large number of entrances. The building buckles back from its northern boundary creating a widening of the street where the offices are accessed. At the building’s prow there is also a double-height loggia providing covered seating for an adjoining bar. Here a lining of pleated green precast-concrete panels interspersed by windows framed in gold anodised aluminium conjures a theatrical mood befitting the venue’s role as a chic night-time hangout.

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Separate doors for the two residential elements are each housed in a deep recess of pharaonic monumentality

The language of green precast elements carries across the upper elevations too.  In perforated form the material conceals opening vents at the sides of each office window while a post allows for the introduction of a partition wall midway across its width. On the apartment floors, vertical posts are again deployed to accommodate internal walls, the eccentricity of their distribution offering a register of the considerable intricacy of the floor plans.  This is a product both of challenge presented by the towers’ compact polygonal form and the client’s desire to accommodate a range of apartment types. Units range from three-bed arrangements designed to serve as low-cost flat shares through to lavish penthouses where the top-lit bathrooms rise to an astounding seven metres. Tenants have access to a communal roof garden situated above the offices but have also been provided with balconies. Recessed into the body of the building these offer a further means of facade differentiation but maintain a reading of the envelope as a taut and almost embroidery-like interweaving of multiple cladding systems.

The road to the south is being widened and trees and public transport introduced. Work is also soon due to begin on the square, the design of which includes the provision of an area of water in front of the office entrance. Particularly happily, the building’s distinctive figure has been taken as a model for the development of the other projects now being constructed on the square. There is good reason to hope that they will read as a considered ensemble and constitute a richly particular piece of city-making.

Mixed Development in Zurich

Architects: Caruso St John Architects, Bosshard Vaquer Architekten

Photographs: Georg Aerni and Hélène Binet

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