Central to the architectural programmes of Matthias Sauerbruch and Louisa Hutton is the whole issue of building sustainability. It was the case with their Berlin GSW headquarters (1999), the Federal Environmental Agency in Dessau (2005) and now with their latest project, the West Arcade building of Frankfurt’s Kreditanstalt für Wiederaufbau (KfW). The brief for the Anglo-German couple from Berlin was to complete the heterogeneous headquarters of this public bank with a single new building. The expressive new construction, embellished with colours in Sauerbruch Hutton style, is Frankfurt’s new urban landmark next to the famous Palm Garden.
The West Arcade is a high-rise with a difference. The brief demanded that energy consumption for the whole complex would not exceed 100KWh/sqm/y. This could only be achieved by adopting special design features allowing real energy-saving measures. The architects’ answer was the “pressurized-ring-façade” developed by them in close collaboration with Stuttgart-based Transsolar.
While the base of the building containing a multipurpose series of volumes has a conventional double-skin façade, the bulk of the elevation has been given a double, “active” frontage. Building orientation was established on the basis of Frankfurt’s prevailing winds. Advantage was taken of the very wide site to set the building at an angle to the very busy thoroughfare, Zeppelinallee. Its arresting shape makes it a point of mediation in this heterogenous architectural context.
The “pressurized-ring façade” is based on a series of operable vents on the outer skin that allow a regular flow of external air into the airspace between the two layers. The system also shelters the building from the strong winds that high-rise buildings usually have to withstand.
Vent position can be changed every 15 minutes, in steps of 15 degrees and up to a maximum inclination of 90 degrees. The automated vent-opening system operates in connection with weather reports relayed from Frankfurt airport. This allows all offices to be naturally ventilated during spring and autumn. The system is supplemented with pre-cooled air in summer and pre-heated air in winter by a geothermal heat-exchanger. The building is connected to the district heating plant while supplementary heat comes from the headquarters’ computer centre. In the winter, if occupants open the windows to air their offices, the heating will automatically shut down, to minimize energy wastage and optimize user comfort for the 700 workers. An overall energy monitoring system will provide feedback on the efficiency levels achieved.
Aesthetically speaking too, the West Arcade building is a key example of sustainable urban design. Shaped like a billowing sail ending in two peaked tips, it evokes Mies van der Rohes famous glass tower on Berlin’s Friedrich-Strasse designed in 1921.The West Arcade is made even more striking by the cladding of overlapping slabs of coloured glass panels on the short sides of the L-shaped facade elements. The result is a fluidity of surface that moves through various tones of colour: blue hues to the East mediate with the surrounding buildings. On the elevation overlooking the main road, the cladding turns gradually from shades of red to green as the building proceeds north to abut onto the city’s botanical gardens, the Palm Garden. When the air vents on the outer skin are open they look like colourless pixels on the wide screen of the façade. The effect, even from afar, is one of natural, unfussy elegance.
The same concern for context and comfort can be seen on the side of the main entrance on Zeppelinallee. Here the ground floor has been recessed to provide a natural canopy for the entrance. Similarly, the interiors present the same distinctive colour scheme and elegant shapes.
The ground floor levels are occupied by spacious foyers and multipurpose areas that look out either onto the articulated inner court of the KfW ensemble or towards the Palmengarten.
The upper floor offices are developed around two adjacent cores whose triangular shape has been softened by rounded corners. Central distribution blocks also contain kitchenettes for staff. The windows at the end of all corridors provide natural lighting and views over the Frankfurt skyline. Full-height glazed doors add to the amount of natural light filtering through the building. A new luminaire called the “Frankfurt Lamp” was developed by Sauerbruch Hutton with Zumtobel especially for the Westarcade Building. It has the potential for serial production. As much as the “Pressurized Ring Facade” does, which Transsolar is already planning to install on another high-rise.