Sauerbruch Hutton

KfW Westarkade . FRANKFURT 

Sauerbruch Hutton . photos: JAN BITTER

The KfW Westarkade is one of the first high-rise office buildings worldwide that can be run with less than 100 KWh/a/sqm of primary energy. The 15-storey, 39,000 sq m extension to the KfW Bankengruppe’s headquarters is completing an existing, heterogeneous ensemble of office buildings from last three decades. Situated in Frankfurt’s West End, it lies adjacent to the central Palmengarten Park. It houses 700 workplaces and a conference centre.

urban concept
The volume of the 56m-tall tower is integrated into the cluster of the
existing buildings. Due to its precise positioning and its curved shape, their skyline remains visible from the streets and views from their offices remain free. Besides providing open sightlines, this streamlined shape aerodynamically addresses the prevailing winds to facilitate controlled natural ventilation for the building.
Towards the ground the volume of the high rise fans out into a gently curved socle defining the street edge, where the façade is set back at ground level to create a protective arcade. The landscape of the Palmengarten is drawn seamlessly into the rear of the site to create a generous and coherent open space.

Both the body of the high rise and its polychromatic skin act as an interface between different distinct urban spaces: while the volume appears as a slim significant slab towards a busy traffic intersection to the south, it presents a discreet backdrop for the landscape of the Palmengarten to the north. To the north-west the building mass appears voluminous and creates an elegant countermovement to the flow of traffic. The various colours of the ventilation flaps of the facade address its heterogeneous context: a group of blues complement the colour scheme and materiality of KfW’s neighbouring main building, while the hues of the red Main sandstone so prevalent in urban Frankfurt are interpreted along the street. A family of green tones fronts the Palmengarten.

sustainability
The highly sophisticated energy concept provides minimal energy expenditure and a maximum of comfort for the employees at once.
The unique double-layered wind-pressurised façade offers very high insulation values, efficient external solar protection and natural ventilation independent of external conditions: dynamically controlled flaps on the outer layer maintain an even air pressure within the double facade, so the windows on the inner layer can be opened individually without undesired heat losses or drafts. A geothermal heat exchanger, thermally activated slabs, heat recovery as well as the recycling of waste heat of the datacentre help to further reduce energy consumption. The cumulative effect of all these passive and active features even undercuts the very ambitious goals of the German standards for sustainable building.

materials
The primary structure of reinforced concrete is used as thermal mass; the exposed soffits of the ceilings offer a surface of pleasant and atmospheric materiality to the office spaces. Coloured glass is also used in the interior spaces. Oak and limestone flooring and high-grade plaster underscore the client’s dedication to providing a high level of comfort in a thoroughly sustainable way.