Radiant star: these new headquarters for a German finance company are a creative reinterpretation of the edge of town office

Architectural Review, The, Nov, 2003

Behnisch, Behnisch & Partner's recently completed headquarters for Entory AG extends the practice's distinguished lineage of humanely conceived, environmentally responsive workplaces. Though not as big a project as the mammoth North Regional Clearing Bank in Hanover (AR August 2002), it still sets challenging architectural and environmental standards for what can often be a dreary and dislocated building type, the edge of town office.

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With a staff of 350, Entory is a subsidiary of the banking and financial services group Deutsche Borse and needed a new headquarters with different kinds of offices--individual, group and open plan--to foster different ways of working, as well as a central social space for its employees. Five German architectural practices were invited to take part in a limited competition for a site on the edge of Ettlingen, a small town just south of the main regional conurbation of Karlsruhe. The area is rural, with fruit orchards to the north and the gentle slopes of the Black Forest to the east, and the site forms part of the transition from densely built-up town to the bucolic open spaces of the countryside.

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With its predominantly permeable aspect and office wings reaching into the landscape, Behnisch's winning scheme responds sensitively to its setting and engages with its surroundings. Two five-storey volumes are arranged in a rough L-shape around a fulcrum of foyer spaces and a staff canteen, but floors are pushed and pulled in the manner of desk drawers sliding in and out, and over and under each other. So what might have been an unremarkable composition has a punchy, animated irregularity, its volumes teeteringly poised like a precipitously stacked pile of books. Here, tiers of floors step back like a ziggurat; there, part of another floor shoots out to be caught and propped up on slim tubular pilotis. Behnisch's characteristic layering of facades and use of colour (overseen as usual by Christian Kandzia) enhances the spirit of animated bricolage, breaking up the building mass and subverting notions of corporate decorum. External blinds shade and screen the glazed envelope and subtly coloured cladding made of a specially developed translucent, photosenstive material changes hue with changing light, like strips of chameleon skin.

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On the non-street side, the two wings enclose a semi-public landscaped garden and pool overlooked by the staff canteen, enabling workers to dine al fresco on fine days. Parking is sensibly concealed in a basement, so that visitors enter at a first floor piano nobile level by a sweeping, almost papal, staircase that traverses a small moat on the street facade. But because of the site topography, this entrance floor becomes the ground level on the garden side.

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Individual office wings are connected by the fulcrum of the luminous foyer, which is surrounded by informal breakout areas, meeting spaces and conference islands. Penetrated by an open stair that dips and swirls up a central void together with a network of galleries and bridges, the foyer is the social heart of the building. Elsewhere, offices are conceived as distinct places, rather than arid, impersonal prairies, with cellular and open plan spaces interspersed to create a varied and changeable internal landscape.

In terms of energy use and environmental control, the building is equally responsive to its users' needs, employing a system based on the principles of thermal mass, natural ventilation and water borne radiant cooling and heating delivered by plastic pipes cast directly into concrete ceilings. Radiant heating and cooling delivers a high level of thermal comfort and avoids the problems of draughts that sometimes beset air driven systems. Heating and cooling are supplied by a combined heat pump and chilling device. The building rests on 150 reinforced concrete piles 8m in length, which act as heat store and exchanger. Water circulates through pipes in the piles and is warmed or cooled depending on seasonal requirements. Heat can be stored in the surrounding ground and when ground temperatures do not match the needs of the building, the heat pump or chiller kicks in to make necessary modifications.

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Apart from in the meeting rooms, canteen and entrance hall, there is no need for a mechanical air supply. All office spaces are naturally ventilated with openable windows, which saves on expensive mechanical systems and reduces the building volume (due to low floor-to-ceiling heights because plenum space is not required).

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One problem with a thermal slab system is that it can be slow acting (because of the huge mass involved), and excessive heating and cooling may occur if weather conditions change suddenly. In this case, a control unit takes account of meteorological forecasts and adjusts the system accordingly, enabling it to respond more dynamically to external conditions. Backed up by building simulation software, the control unit is fine tuned to avoid excessive heating or cooling without loss of overall thermal comfort. Compared with a similarly sized building, Entory's architects and engineers predict that its energy consumption will be considerably reduced, but its success, as with other Behnisch office projects, also lies in the way it humanizes and civilizes the environment of the corporate workplace.