Potsdamer preview.

The first building in the initial stage of the huge Potsdamer Platz development which is intended to give Berlin a new heart.

History

Potsdamer Platz was one of Berlin's most important squares before the War: not very beautiful, either in urban form or architecture, but full of life, trams and traffic, always changing - a German equivalent of Piccadilly Circus or Times Square with sometimes a decent building like Schinkel's gatehouses and Mendelsohn's Columbus Haus. Bombs and shells put an end to most of the buildings. Then came the Wall, and almost everything that was left was razed to allow the guards a clear field of fire over the desolate minefields.

When Germany was reunited over a quarter of a century later, it was clear from the start that a lively new Potsdamer Platz would have to be created as a symbol of the rebirth of the city and nation. With the Wall removed, the site could once more relate to its neighbours, the Landwehr Kanal to the south, with the Tiergarten park and the Reichstag a short distance to the north. Scharoun's great buildings, the Philharmonie and the Preussischer Staatsbibliothek could be brought into urban conversation, whereas they had previously been forlornly isolated up against the Wall.

A working group was set up by the Senate of Berlin in 1990 and a competition held for the whole site south of the Tiergarten, east of the library and west of Leipziger Platz. Entries and results (announced in 1991) were controversial, with Hilmer & Sattler producing a rather timid first prize scheme (which fulfilled the intentions of City Architect Hans Stimmann and Wolfgang Nagel, Berlin senator in charge of building to create a 'critical reconstruction' of the pre-1940 plan by retaining most of the old street pattern). O. M. Ungers collected second prize for a rationalist cluster of towers intended to mark the place on the map of Berlin (and Europe), but this was seen as too arrogant a gesture by the jury.

In 1991, the owners of the sites within the redevelopment area (huge companies: Daimler Benz, Sony and others) commissioned Richard Rogers to make a counter masterplan. In 1991, he produced a very formal ahistorical scheme radiating from a glazed circus which locked into the octagon of Leipziger Platz; the proposal successfully linked all the major elements in and around the site in a genial urban scale (AR January 1993, p21). The Senate turned the proposal down, but asked Hilmer & Sattler to incorporate some of Rogers' ideas, particularly natural ventilation and lighting of the buildings, into the masterplan.

The plan

The landowners were required to develop within the Hilmer & Sattler masterplan and each held further competitions. First prize in the Daimler Benz one went to Renzo Piano with Christoph Kohlbecker (AR November 1992, p4). The winner of the Sony competition was Helmut Jahn. The Daimler-Benz site is the most southerly one. To the north, before you get to the park is the Sony triangle where Jahn is building offices (including the firm's European headquarters), housing and shopping spaces round a giant ovoid urban entertainment centre which will contain the Filmhaus and Deutsche Mediathek, as well as an IMAX and numerous cinemas. To the east of the Piano site, is Linkstrasse, which will have a green linear park in its centre (is this a wise move?) and, on the other side, is to be a series of courtyard blocks on the A+T site designed within Giorgio Grassi's overall plan by different architects including Roger Diener and Jurgen Sawade. All these sites meet at the Potsdamer Platz itself: an irregular public space, not unlike the old one. It adjoins Leipziger Platz, which is to be recreated on its old octagonal plan (the hamfistedness of its first new building sadly promises some sort of scaleless neo-poMo extravaganza here).

Piano's parti for the Mercedes Benz site is not very complicated to understand in principle. (Though it is difficult to comprehend at the moment in the midst of the vast turmoil on the largest building site in Europe, all of which is amazingly intended to be completed at the end of this year.) From Potsdamer Platz, an avenue, Alte Potsdamer Strasse, lined with mature trees (which astonishingly survived all the destruction) runs south-west to the opposite side of the development area. Here, Marlene Dietrich Platz, a new pedestrian square is to be created, appropriately cradled in the arms of a new casino and a music hall. These back onto the great blank gold east wall of the Staatsbibliothek, into which it is hoped at some time to make a new entrance from Marlene Dietrich (though the library authorities are at the moment opposed to the move because of disruption caused by the colossal works to their east). The other major geometrical moves in the urban plan are retention of the traditional lines of north-south Linkstrasse and the boomerang of strangely named Eichhornstrasse (Acorn Street). From this simple matrix, the other thoroughfares of the complex take their pattern, much as would the minor streets of a nineteenth-century city after its main lines had been laid out.

Architects and planners were determined from the first to make sure that the new city centre should have a real urban mix of uses: as well as offices, there will be housing, shops and restaurants, a hotel, a cinema, big screen 3-D theatre, the casino and music hall. As in the A+T development across Linkstrasse, the Piano site has been divided among several architects, for masterplanner and client decided that the area and its 17 blocks were too big to be created by one firm (all participants won prizes in the Daimler Benz competition). Apart from organising heights, street pattern and distribution of functions, Piano and Kohlbecker suggested that cladding should be in glass (of course), and terracotta with details and precise colours chosen by individual architects. On the whole, the suggestion has been followed, with only Rafael Moneo deciding to use different material, sandstone (though the stone's colour is within the terracotta range of the spectrum).

Moneo is building the hotel and the housing block on the north side of the site. Rogers is doing three eroded cubes of offices, retailing and flats which face east across Linkstrasse. To the south of these is Isozaki's contribution, a rectangular commercial block with parallel slabs along a long atrium. This was the first building to be completed, and promises to be the least impressive, with flush facades of two-tone terracotta arranged in meaningless trapezoids topped and underskirted by frilly undulating glass walls. A 23-storey high office tower by Hans Kollhoff will bring the complex to conclusion against Potsdamer Platz in the north-east. Over Alte Potsdamer Strasse, Piano is making a slightly shorter tower, so that the pair of tall buildings will make a gateway from square to street.

Piano's office is making a swing of buildings down Alte Potsdamer Strasse down to the Landwehrkanal at the southern end of the site. To the west, the curve defines the edge of the Marlene Dietrich Platz, looking over toward the music hall and casino (also by Piano). To the east, the Piano work is to be linked to Rogers' three cubes by a glazed shopping arcade. Some notion of what the area will be like in a year's time can be gained from the Piano's first building to be completed: the Mercedes Benz Haus at the southern tip of the complex.

The building

As you drive east along the Landwehrkanal, there is a procession of monuments on the north bank: first Stirling and Wilford's now rather faded pink and blue striped postmodern Wissenschaftszentrum, frivolous in comparison to the gravitas of Mies's dark square steel and glass Nationalgalerie; then the Staatsbibliothek, the alternative strain of Modernism flexing and twisting in concrete and gold aluminium, then a Wilhelmine Baroque villa, the only reminder in this part of the bank of what the canal must have looked like in the nineteenth century. Then the climax: Piano's 21-storey Mercedes Benz tower, resplendent in eco-tech layered cladding of glass and biscuit coloured terracotta.

Though this is quite the biggest building in all the procession (at least in height), it does not show off. It has distinguished and elegant modesty, appropriate for what is mainly a large office block. After all, all the other creatures in the zoo along the canal are in one way or another monuments to culture built with public money, so it is appropriate that the first commercial building in the sequence should act as dignified backdrop. But it succeeds in avoiding both the pinstriped effect of so many curtain wall buildings and the aggressive dullness of Isozaki next door.

South and west sides of the tower have a glass breathing wall with a Iouvred outer skin which is opened and shut automatically and an inner layer of tilt and swivel windows which ensure that individual inhabitants of offices can adjust their own internal climates by taking tempered air from the 700mm wide cavity. This would appear to be a much cheaper way of making a breathing wall than the elaborate special sections used by Foster and Ingenhoven in their office towers in Frankfurt and Essen (AR July 1997). And visually, it is more delicate and subtle, with the outer glass skin often fluttering and changing, and the two glazed layers with their interstitial space clearly articulated against each other.

The east side of the tower is quite different. Here the terracotta cladding (a few elements of which you can glimpse in the cavities of the breathing walls) dominates the whole facade as a skeletal exo-skin. Vertical and, predominantly, horizontal terracotta elements are combined to create a delicately proportioned pattern which articulates each floor and bay within an overall texture. In a sense, this is a huge modern ceramic mashrabiyya, which modifies the impact of the elements and provides a protective framework for the louvred blinds that can be lowered in the external cavity between ceramic and glass skins. The terracotta pieces themselves are of course specially made (by NBK): the horizontal ones are hollow extrusions which Piano calls 'baguettes'; the vertical pieces are more like beads which are fixed back to the metal subframe of the tilt and swivel office windows and the automatically operated ventilation lights above them. Baguettes lock into appropriate beads and the whole assembly - windows, spandrel and terracotta elements - is delivered to the site as a storey-height prefabricated unit.

To the north are three lower, longer building pieces between seven and nine floors high. These have the same biscuit-coloured cladding as the east front of the tower and all round them is a double-height external arcade which allows glass walls to offer local street level activities (though when I visited the building last month, virtually the only signs of this were a cafe and a showroom for Mercedes Benz vehicles).

The north entrance at the tip of the lower part leads directly to an atrium which runs through virtually the whole length of the lower parts of the complex. This nave-like volume is toplit from a glass roof and the double-height arcades are expressed on the interior down the two long sides. Here the cafe, car showroom and a travel agency open into the big space (and will presumably be joined by other such uses as the area gets going and attracts more people than those who work for the Daimler Benz development and management company which occupies this first finished building).

In the atrium, the main vertical structural elements are emphasised by being clad in flat terracotta bats, rather like the ones Piano used on his housing in Paris, but similar in colour to the baguettes, which themselves re-appear in various ways covering service ducts and the narrow ends of the big space. Between the rectangular terracotta covered columns are regular strips of aluminium tilt and swivel windows, which like those on the external walls can be manipulated by inhabitants of individual offices. Strips of windows between biscuit-coloured columns do not sound like a very promising recipe for making a fine space, but their potentially drear effect is ameliorated by a simple device: layers of glass slats fritted in white with a delicate pattern are above and below the window strips. Set sloping upwards at 45 degrees, their laciness softens the space visually - and acoustically for they act as sound diffusers and act with the absorption behind pierced aluminium spandrels. Their laciness is echoed in the slats held at 42 degrees under the roof to modify direct sun.

The atrium is the first of what promises to be a sequence of many major public and semi-public spaces which will be created in the Potsdamer Platz complex, and while there may be arguments about the nature of ownership and control (p5), the propriety and elegance of the new space and the building that houses it cannot be questioned. Astonishingly, the rest of the vast site is to be completed within a year. The start is what a schoolmaster's report would call 'very promising indeed, but a long way to go'.

Renzo Piano Building Workshop/C. Kohlbecker

Design Team B. Plattner (associate in charge), R. Baumgarten, A. Chaaya, P. Charles, G. Ducci, M. Kramer, N. Mecattaf, J. Moolhuijzen, J. B. Mothes, M. B. Petersen, J. Ruoff, M. van der Staay, E. Volz With E. Audoye, G. Borden, C. Brammen, D. Drouin, B. Eistert, M. Hartmann, O. Hempel, M. Howard, W. Matthews, G. M. Maurizio, D. Miccolis, M. Pimmel, S. Stacher, M. Veltcheva

Kohlbecker team: J. Barnbrook, H. Falk, A. Hocher, R. Jatzke, M. Kohlbecker, M. Lindner, N. Nocke, A. Schmid, W. Spreng

Engineers Ingenieurgemeinschaft IGH/Ove Arup & Partners, Schmidr Reuter Partner; Ingenieurgemeinschaft Boll & Partners GmbH, Stuttgart, Ove Arup & Partners, Ingenieurgemeinschaft IBF 

Landscape Mohrle und Kruger, Stuttgart, Berlin

Facade construction Gotz

Terracotta panels NBK Keramik

Photographs Berengo Gardin, Vincent Mosch, Michel Denance, Andreas Muhs