KfW Skyscraper A Stroke of Luck, not the Rule

It’s not excessively high at all, the skyscraper of the Kreditanstalt für Wiederaufbau KfW in Frankfurt am Main. It’s enough of a skyscraper in spite of this, as the distinction of the internationally renowned Annual Award for 2011 as the world’s best skyscraper by the Council on Tall Buildings and Urban Habitat (CTBUH) in Mies van der Rohe’s Illinois Institute of Technology in Chicago demonstrates.

KfW-Skyscraper in Frankfurt KfW-Skyscraper in Frankfurt | Photo: Sebastian Melzer The KfW, a public-sector bank whose tasks include handling financial transactions relating to government subsidy measures, primarily promotes building measures that serve energy and ecological optimisation. No question that the bank wished to lead the way with its own office buildings as a shining example of sustainability. And thus it was with the new “Westarkade” expansion at the bank’s established location in Frankfurt am Main. The 14-storey building for the IPEX Bank arose right next to the Palmengarten city park. IPEX is a KfW subsidiary that handles financing for German investors abroad, for large-scale ships, for instance.

Innovation and symbolic presence

Matthias Sauerbruch and Louisa Hutton from Berlin are the new building’s architects. They count among those architects who took up the theme of ecology early on. With the GSW skyscraper in Berlin they had also realised an award-winning building with comparable dimensions, one which highlighted innovative paths in terms of energy technology and set an example with its distinctive colour concept.

In Frankfurt, the KfW aimed for both technical innovation and symbolic presence with the building, which was to stand out from monotony of office building construction in spite of its moderate height by Frankfurt standards.

Facade in a play of colours and patterns

The result is unquestionably a success. Motorists have no choice but to lift their gaze and take a look at the tower. And they must then lower their gaze due to traffic before they have properly grasped the principle of the façade’s design. The building with its thousands of pixelations plays with colours and patterns like a picture puzzle, and changes its colours like a chameleon. The colour subcarriers are only the narrow ventilation flaps that jut out like the teeth of a saw, and whose visibility moreover depends on their individual opening angles. Red tones corresponding to the red sandstone to be found in Frankfurt and the city’s red clay tile roofs predominate along the Zeppelinallee. The building responds with blue tones to the firm’s neighbouring steel-blue main building, while green tones prevail facing north towards the Palmengarten.

Sophisticated ventilation technology

The construction of the double facade of prefabricated elements is also responsible for the façade’s unusually complex appearance. The external façade consists of storey-high glass elements, the inner facade of a double glazing in heat-insulated aluminium profiles. Every second inner window can be opened, so that fresh air can enter individual rooms in a weatherproof fashion by means of the narrow external ventilation flaps. The flaps are part of the sophisticated ventilation system, which works with a “compression ring” between the façade layers. The streamlined form of the building itself was designed with this in mind, and aligns itself with the prevailing wind direction. The pressure can be automatically regulated with the ventilation flaps. Exhaust air is vacuumed up inside and heat recovery is fed in. In addition, a ground duct serves to temper the fresh air. Thus the optimal energy conception is enabled in every case – summer and winter, day and night, cooling and heating –through intelligent management of the building’s technical systems.

Flexible, light-filled atmosphere

The building’s ground plan produces sweeping, curved corridors illuminated with daylight, perfectly detailed by the architects with red linoleum flooring, floor-to-ceiling glass doors, contrasting shadow gaps and round luminaires. The ground plan system allows for a variety of office constellations, even though only individual offices were built at first. Those who enjoy letting their gaze wander will be able to work with full concentration only if there is fog, since the generous glazing offers splendid views of the surroundings and the city skyline, especially from the upper storeys.

If one considers the requirements that an inner-city skyscraper must meet today – moderate height, dialogue with the neighbourhood, optimal interior and workplace features, economical and sustainable construction and operation – this building fulfils them impressively. The fact that average citizens also think this office building is beautiful and interesting is a stroke of luck, and by no means the rule.