The facades of the new premises of the European Central Bank (ECB) consist of glass, clinker bricks, concrete and metal. The Grossmarkthalle (Frankfurt’s former wholesale market hall) is characterised by concrete grid and clinker facades, while, with their glass and metal facades, both the double office tower and the entrance building are clearly identifiable as new.
The characteristic brickwork and concrete grid facade of the Grossmarkthalle have been restored in close cooperation with the historic preservation authorities. Image gallery
Extensive repair work has been carried out on the brick facades of both wing buildings. Any bricks that were damaged have been replaced with those collected during the removal of the annex buildings. All the joints of the brickwork have been raked out and, in keeping with architect Martin Elsaesser’s original design, filled with two different colours of mortar – a pale mortar for the horizontal joints and a dark mortar for the vertical joints – in order to accentuate the horizontality of the brick courses.
The eastern wing building used to house the market’s cold storage rooms and so its facade had virtually no windows. In agreement with the historic preservation authorities, space has therefore been created in its brickwork for rows of windows, so that its facade is now similar to that of the western wing building. As for the windows in the staircases of the two wing buildings, the old steel frames have been fitted with new glass panes.
The concrete grid facades on the northern and southern sides of the Grossmarkthalle have been carefully repaired and cleaned, and all the windows, with a few exceptions, have been replaced. The steel frames of the new windows have been constructed in such a way that they are as narrow as the old ones, but strong enough to support double glazing. Additionally, the new windows are much more energy-efficient than the old ones.
The brick facades of the ground and first floors of the market hall have been removed and replaced with rows of windows, in order to let in more natural light. The windows on the northern side have been fitted with thermal insulation glass, while those on the southern side have been fitted with glass that provides both sun protection and thermal insulation.
The brickwork of the outermost wall of the front extension on the northern side of the Grossmarkthalle is being fully restored. Three of the original windows have been restored and fitted with new glazing, while the others have been replaced with new ones consisting of narrow steel sections and a single pane of glass, resembling the original ones. The original steel bars have also been restored and mounted in front of the three original windows.
In line with the "house-in-house" concept designed by the architecture office COOP HIMMELB(L)AU, the conference area and staff restaurant have been integrated into the Grossmarkthalle as separate building elements. These have a structural framework of steel posts and beams, and individual facades consisting of thermal insulation glass. While the new building elements are enclosed units with their own temperature regulation system, the open areas of the Grossmarkthalle surrounding them will be affected by the seasonal air temperatures outside.
The two office towers and the transparent atrium that joins them together are conceived as a monolithic glass structure. Image gallery
A combination of different geometries makes the double office tower look like a large crystal, with oblique surfaces on the western and eastern facades and hyperbolic paraboloid surfaces on the northern and southern facades. A hyperbolic paraboloid surface is essentially a concave curved surface that is produced by moving an open-down parabola along a fixed open-up parabola. What is important, however, is that the hyperbolic paraboloid surface can be produced through two sets of straight lines, so that the hyperbolic paraboloid can be constructed from rectilinear elements.
It is this principle that formed the basis of the facade design for the high-rise. The towers have been fitted with flat glass panels, 90% of which are identical to each other. Each panel runs the entire height of a single storey, so that only the vertical fixings are visible. The result is a homogeneous curved glass surface made up of straight panels.
This surface consists of a state-of-the-art "shield hybrid facade", which comprises three layers and is a refined synthesis of classic facade constructions, combining the functions of box windows, double-glazed windows and double facades. In order to meet various requirements relating to fire prevention, the reduction of radar reflection, the cleaning of the facades and sun protection, a special type of glazing was chosen, consisting of sun protection glass on the outside and thermal insulation glass on the inside. Aluminium blinds are also fitted between the two panes of glass to enhance the level of sun protection.
The offices will be air-conditioned, but there will also be the possibility of natural ventilation through the use of a new opening mechanism, whereby the panes move out horizontally from their frames. This mechanism is "hidden" behind the outer facade and supplies the offices with outside air through the ventilation slots that it creates. If the individually adjustable ventilation slots are open, the air conditioning system in the respective office automatically shuts off in order to conserve energy. The opening panels can be fixed in any position by means of motor-driven hinges.
The panes of glass for the facade of the atrium – which connects the two polygonal towers – are mounted on a customised steel grid. It is strong enough to bear the weight of the glass panels along the full height of the atrium and is therefore clearly visible through them. In line with the design concept, the glazing of the atrium is neutral in colour and transparent. This enables people to see straight through the atrium and view the high-rise as two separate towers. This impression of a transparent atrium is enhanced by its roof, which is also made of glass. The glass is coated in such a way that it absorbs less than 10% of the energy from the sun, though the sky can still be seen through it.
The distinctive entrance building, in the foreground of the double office tower and the long horizontal expanse of the Grossmarkthalle, will round off the building ensemble and define the look of the ECB. Image gallery
The entrance building projects out of the Grossmarkthalle by about 20 m in the direction of Sonnemannstrasse. Its northern facade, behind which the press centre is located, is particularly striking: in contrast to that of the double office tower, it is a three-dimensionally curved surface consisting of hyperbolic glass panels.
The walls of the entrance building, as well as its underside, will be covered with aluminium sheets, while panels of glass will break up the concrete grid facade of the Grossmarkthalle, clearly marking the main entrance to the ECB.
Further information on the facades can be found under "Publications Other publications" in our new premises media centre