Cultural crossroads: a dramatic new entrance to the Graz exhibition grounds houses a multi-cultural space suitable for all seasons

Architectural Review, The, July, 2003 by Peter Blundell Jones

As Austria's second city and one of few large, urban centres in a generally mountainous country, Graz has for centuries been the site of an important fair. Its twentieth-century fairground lies in the southern suburbs alongside one of the original main roads that radiate from the Schlossberg. This year, Graz is European City of Culture, celebrated among other things by a handful of building projects. The most important of these are the yet unfinished Kunsthaus by Peter Cook and Colin Fournier, and Klaus Kada's Stadthalle, both the result of architectural competitions.

The Stadthalle is a multi-purpose hall and conference centre, but it also serves as the new grand entrance to Graz's fairground. The greater part of it is a single volume 95m by 70m in plan and 15m high with variable seating. It can serve as an exhibition hall, a sports arena, a pop-concert venue or whatever.

This set the scale for the whole, prioritized the need for a wide-span structure and could easily have resulted in a rather inhuman and overwhelming building. At the same time, the demand for flexibility made it difficult to give this main room any definitive character. Kada solved these problems by skilful response to the context, allowing ancillary parts to break the symmetry and to mediate the scale between the vast and the intimate.

Unlike Mies's famous project for a congress hall in Chicago, a big regular box largely concerned with showing off the discipline of its steel structure and bracing, Kada has remained much more ambiguous about spatial boundaries, even putting main columns outside the space of the main hall. While Mies suppressed the roof, at least from the outside, Kada stresses it as the primary element and plays down the visible structural effort.

The main idea is a big roof supported on only four columns. The space embraced by them is almost square, but the covered area is more than doubled in length by huge cantilevers to east and west. These are supported by steel trusses that taper with reducing stress, leaving a rising soffit that diminishes to a pointed edge. Since the building is hemmed in at the sides and visible only from front and back, this successfully conceals a structural depth in the roof space of about 6m, while the biggest elements of horizontal structure, the steel trusses linking north and south columns, are silently absorbed. The roof space is largely filled with equipment and service ducts, including the usual air-handling plant, as well as huge venting machines to clear smoke quickly in case of fire.

The main hall takes up most of the central span and the space under the east cantilever, while the one to the west projects out over the street to provide an entrance portico and foyer. To disrupt the boxiness of the hall and replicate something of the portico on the other side, Kada has made the side and end walls openable with a long series of electrically driven swing doors. When open, they make the point that the building is not a free-standing entity, but rather the entry point to the whole fairground behind, and the effect should work well when the main space is used as an exhibition hall in warm weather. A great window to the foyer on the west side gives the hall daylight and a sense of direction, although initial plans for strips of daylighting through the roof were dropped. A flat floor and a variable seating system allow for many configurations, and a suspended lighting grid marks the potential stage to the east.

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The conference centre is treated as an ancillary building that both adjoins and invades the space defined by the primary structure. It embraces the hall to the north and west in an L-shaped arrangement at first floor level, its west part tucked under the main roof and its north part free-standing. The north-west corner ends in a nine-storey block of offices reaching out to the normal building line. Its outwardly splayed north edge set against its concrete escape tower provides a vertical accent to balance the dominant horizontal.

Also crucial to the whole composition is placing the conference plenary auditorium as a projecting box under the main roof, half in and half out of the foyer. In this position, it mediates between the scale of the other parts but provides a recognizable climax for people who use only the front part of the complex.

Other conference rooms are placed at the back of the foyer and in a separate wing along the north side, and the whole conference suite culminates in a two-level bar/restaurant at the north-west corner next to the main escalators with views down to the entrance.

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As in earlier buildings (ARs November 1989, April 1990, February 1992, November 1993, June 1997, May 1998, March 2000), Kada has glazed gaps between the building parts to emphasize their separate structures and their in-between-ness, providing top and clerestory lighting, so the foyer spaces have become a series of brightly lit internal streets. The main plenary conference halls also have strip windows, giving views onto the street, and there is even a high-level external balcony tucked in above it yet still under the main roof, with views across the city to the mountains beyond.