The KfW Westarkade offices and conference centre in Frankfurt are too green by half, says Felix Mara. Photography by Jan Bitter
More from: Sauerbruch Hutton
There’s something about sustainability that’s very close to the German soul. Interest in sustainable building gained momentum in the 1980s, when Germany had a high-profile Green Party whose ideology pervaded the architectural profession. But in the UK, although the 1973 oil crisis had focused architects’ attention on energy conservation, the more altruistic remained preoccupied with social equality.
Sauerbruch Hutton Architects set up shop in London in 1989, but in 1993 it opened its Berlin office, in founding partner Matthias Sauerbruch’s homeland, which was to become the main focus of activities. Given this timescale, green building was naturally on the practice’s agenda, albeit seen from an independent and critical perspective, integrated with a broad and artistic approach to design.
In this context, Sauerbruch Hutton’s appointment by the government-owned German development bank KfW to design Westarkade, an exemplary green office building inaugurated in July 2010, was an ideal commission, but it was also a mixed blessing.
Given the size and scope of Westarkade, with 700 workplaces and a conference centre on its Frankfurt am Main ‘campus’, you could draw parallels with significant projects such as Denys Lasdun’s European Investment Bank in Luxembourg, Norman Foster’s Hong Kong and Shanghai Bank or Richard Rogers’ headquarters for Lloyd’s.
It also offered enormous potential to push low-energy sustainable design to its limits as an integral part of a building of the highest quality. But this architect’s hog heaven carried a dual penalty. First, KfW impeded Sauerbruch Hutton’s vision and second, its gratuitous chequebook reduced the pressure to design economically, which is part of the sustainability challenge, one of the rules of the game.
‘Impeded’ is perhaps a strong word when speaking of an indulgent and understanding client, but KfW curtailed Sauerbruch Hutton by rejecting its proposal for open-plan office space, which would have had much more visual appeal. The option for KfW to ‘knock through’ is still there, but it must contend with fierce opposition from its staff, who are still wedded to the German cultural norm of cellular offices.
It also wanted three stories of basement car parking, which is about as green as you can’t get. Twenty-five per cent of the parking allocation is for use by members of the public visiting the adjacent Palmengarten. Perhaps this could be described as ‘social sustainability’, but it’s hardly a stance against Germany’s deeply-entrenched petrolhead culture.
But to put this in perspective - KfW, who among other activities provide finance for investment in domestic energy efficiency and environmental protection - set out to make a green architectural statement. It wanted one of the first high-rise offices in the world with a primary energy consumption of 100kWh/m2 per year - 15 storeys is high-rise by German standards. And the armoury of eco-design features is impressive, not just on the level of metrics, but also for the sheer force of the design team’s imagination.
The chief move was a twin-wall facade that uses horizontally pivoting flaps of varying size to regulate the air which flows through it while maintaining uniform pressure in the cavity. This enables the building’s occupants to open windows - another cultural expectation of German office workers according to Sauerbruch Hutton architect Caroline Wolf - without compromising its environmental performance.
Other green features include natural ventilation, narrow offices that maximise daylight penetration, activated floor slabs with their temperatures controlled by hot and cold water, a geothermal heat-exchange system, high insulation levels, heat recovery, presence sensors and venetian blinds in the cavities that reflect daylight into the building.
KfW’s insistence on the highest level of occupant comfort could be seen as excessive, and it might have been better if it were more relaxed, for example in its requirement for extensive environmental control back-up. A leaner, less ostentatious building would have been possible, with less capital expenditure on eco-bling.
More than this, because Sauerbruch Hutton was hell-bent on perfection in the building’s performance and detailed design, it failed to achieve clarity in the overall vision - a case of not being able to see the wood for the trees, one might say. The hues of the ventilation flaps on each ‘side’ of the tower respond to their context: green for the section facing the Palmengarten, red for the more urban Zeppelinallee elevation, to resonate with Frankfurt’s sandstone facades; but the pleated geometry of Westarkade’s envelope dissolves the clarity of its architectural form, and its myriad colours mix optically, like Missoni knitwear, to melt into a grey mass.
Zoom in and you return to the beautiful world of the detail, the materials and the vivid colour - the qualities which come to mind when Matthias Sauerbruch refers to the joie de vivre which is needed to sugar the bitter pill of Westarkade’s earnest green convictions.
Start on site May 2007
Completion July 2010
Form of procurement Competition won in 2004
Client KfW Banking Group
Architect Sauerbruch Hutton
Structural engineer Werner Sobek
Energy consultants Transsolar Energietechnik
HVAC consultant ZWP Ingenieurs
Electrical consultant Reuter Rührgartner
Main contractor ARGE Züblin / Bögl
Estimated primary energy consumption 98kWh/m² per year
Annual final heating energy 44kWh/m²
Annual cooling energy load 6kWh/m²
Average U-value for windows 1.1W/m²K
On site final energy generation 65%