The tasks a façade has to fulfill in contemporary high-end architecture have become more and more complex and challenging. An innovative skin has to block a considerable amount of sun radiation in summer, while it has to prevent heating energy from getting lost in winter. On the other side the iconic character of “signature” architecture pushes for glass façades to become almost dematerialized, a development further reinforced by recent advances in modern glass technology. Contemporary façades have to reach high transparency rates and have to follow extremely complex geometries – while still fulfilling requirements with regard to energy consumption and user comfort.
Some question whether the extensive use of glass in facades is sustainable. We believe that even fully glazed facades can be sustainable, provided they are designed and engineered accordingly. A sustainable façade has to allow for (controlled) natural lighting and (controlled) natural ventilation and reduce energy consumption to a minimum, allowing the latter to be offset by the use of renewable energy sources, such as solar or geothermal energy. Moreover, materials used should be kept to a minimum and be recyclable. A proper combination of transparent and opaque parts may become fundamental in the search for a synthesis of transparency and sustainability – while keeping in mind that glass is a building material that can also be used for opaque buildings skins. In certain cases the client and the architect call not only for transparent and sustainable skins, but also strive for extreme geometrical complexity. The engineering work is then even more challenging, because of the increased difficulty in detailing, producing, and erecting such kind of facades.
The individual solutions presented in this paper show some possible answers on how to address the challenge of achieving facades that are transparent, complex and sustainable at the same time. The innovative character of certain solutions requires that all the involved parties from the clients up to the contractors share the will to push the boundaries within a reasonable extent.
A selection of recent projects show the different approaches and solutions developed by Werner Sobek for skins that not only fulfill the formal and aesthetical demands of contemporary architecture, but which are also sustainable – both with regard to their resource consumption and their influence on the overall energy consumption of the building.
Transparent and sustainable skins
Doha Convention Center, Quatar
The recently opened Doha Convention Center in Qatar aims at strengthening the role of Doha as a business hub in the Middle East. A special feature of the building is the transparent cable-stayed facade at the entrance areas along the southern and western sides of the building. How can such highly transparent facades be sustainable in a Middle Eastern climate? The answer lies in a combination of different solutions such as a cantilevering roof, a 10° façade inclination and the use of coated insulated glass units. Sun shading elements and partially opaque sections at the eastern and northern sides of the building allow for the overall energetic balance of the building to be further optimized. The entrance facades have been engineered by prestressing stainless steel cables horizontally over max 180 m between two bow-strings. A more traditional vertical layout of the cables was not possible, since the long-span roof could not be used for vertically prestressed cables. The south façade (which is 297 m long) was therefore divided into two segments, thus matching the movement joints of the main structure. Each facade segment is subdivided into modules by hinged steel columns. These columns are 20 m high and stand at a distance of 18 m to each other. They reduce the free span of the cables under horizontal loads and also act as tie-backs for the roof structure.
The insulated glass units measure 3.0 m by 1.4 m. Their dead load is hung from the top by tension rods which are placed at every vertical joint. The glass clamps are placed at a distance of 300 mm from the vertical joints. The free span could thus be reduced and the glass thickness optimized. The cable clamps transfer wind loads to the cables just by contact; therefore their size could be kept to a minimum. Given the long spans to be dealt with, keeping control of horizontal deflections and of the resulting warping in the insulated glass panes was a particular challenge. Steel fins with different heights were therefore planned at the top and the bottom. Their specific stiffness against wind loading allows for an optimized and gradual deflection shape, thus reducing the amount of warping at the corner glass units. All the details and particular solutions developed for the Doha Convention Center help to increase the level of transparency to an astonishing level. The coherent approach towards minimizing the loadbearing structure not only confers a very elegant appearance to the façade, but is also an important contribution towards making the structure sustainable with regard to the use of natural resources.
Maison de l’Histoire Européenne, Brussells
The ‚House of European History‘ will soon offer visitors the opportunity to learn about the history of Europe and to take a critical look at the questions facing Europe today. The project was planned and designed by Paris-based architects Chaix & Morel and JSWD Architects from Cologne. The museum is housed in a former dental clinic, which had to be comprehensively refurbished and extended to be able to fulfill the requirements of a modern museum. The conversion plans include an extension on the courtyard, which is enclosed on three sides, as well as the addition of three stories.
The new facade has been conceived as a double skin façade: The outer skin consists of an energetically sustainable mix of opaque and transparent glass elements; the former are placed in front of concrete cantilevering boxes, the latter are stiffened by glass fins and set in front of a triple-glazed thermal skin. Openings in the outer skin have been optimized to allow for natural ventilation of the cavity between inner and outer skin, so that cavity overheating can be prevented. The façade offers a high degree of transparency in combination with excellent user comfort and an efficient energy system. The transparence is enhanced by the use of glass fins and by the bracing effect of the skin laminated glass panes. The height of the fins varies and reaches up to 14 m at the two western corners. Both the transparent and the opaque elements forming the outer skin have a custom designed line pattern printed on them: this optimizes the amount of solar energy passing through the outer skin and at the same time gives a uniform appearance to the whole facade.
Iconic and complex skins
Enzo Ferrari Museum, Modena
The museum dedicated to Enzo Ferrari in Modena plays with the duality between the renovated historical building where Ferrari was born in 1898 and a futuristic exhibition gallery designed by the late Jan Kaplicky (Future Systems, London). The gallery embraces the masonry building, whereas its sculptural form is clearly inspired by sport car design. From the gallery the view converges through the transparent curved façade to Ferrari’s birth house – it is as if you were looking through an oversized car windshield. The glass façade is made of insulated glass units with argon filling; this helps to reduce heat losses in winter. Horizontal sun shading elements and solar control coatings reduce the cooling loads in summer, still allowing for a high degree of natural lighting for the exhibition area. The overall energy balance is optimized through the high performing metal skin. Below the yellow coated aluminum profiles, thermal bridges have been avoided by using a foamglas insulation layer with a custom developed adjustable point support system. Cooling and heating are provided by a special geothermal type of heat pumps with thermal exchange elements placed underground at a depth of 130 m.
Given the geometrical complexity of the building envelope, the engineering philosophy chosen for the façade of the Enzo Ferrari Museum in Modena was to maintain a relative simple geometry for the facade panels. These were adapted to the different geometrical situations by means of complex customized detailing. The geometry of the 11 m high cable-stayed glass façade is defined by two intersecting conical surfaces, which inclined towards the interior by 12.5°. The sinuous form of the façade was accomplished using 32 mm stainless steel cables and mainly regular planar glass units. A curved hollow steel girder constitutes a top-side support for the cables and outlines the complexity of the edge, which results from the intersection between the roof surface and the conical façade surfaces.
The girder has a length of 62 m and a diameter of 1,000 mm and is made of 13 single-curved segments which were fully welded on site. Special attention was paid to controlling the deflections of the whole façade as well as the warping of the most critical insulated glass units by optimizing every single cable pretension force. The façade engineering of the Enzo Ferrari Museum was a considerable challenge, due to the required transparency and the geometrical complexity in conjunction with the energy and comfort requirements that had to be met. Such complex freeform skins call for a change in the planning process from 2D drawings to 3D digital models. Despite the computational progresses in approaching such complex skins, the detailing, production and erection of such envelopes remains a very demanding task.
Fraunhofer Institute, Würzburg
The competition for the extension of the Fraunhofer Institute for Silicate Research in Würzburg has been won by Zaha Hadid Architects with the idea of using glass only as skin material for both the transparent and opaque areas, as a reference to the silica research objective of the institute. This also leads to a sustainable approach to the energetic balance of the building. Geometrically the five-storey building follow the course of the ‚Luitpoldstraße‘ before swinging around towards the existing buildings and leads to a very complex three-dimensional external envelope.
Due to the architectural wish to exclude any visible fixings, Werner Sobek developed an innovative solution and tested it on a full-scale prototype. Monolithic glass panes were curved by using special molds and backpainted with polyurethane to allow for a residual safety mechanism in case of glass breakage. In general, the glass cladding is fixed to a steel truss substructure by means of aluminum adapter frames, with screws inserted through the joints between the panels. The frames are bonded with structural silicone at the back of the panels.
Werner Sobek has designed many iconic skins. The individual solutions presented in this paper show some possible answers on how to address the challenge of achieving facades that are transparent, complex and sustainable at the same time. The innovative character of certain solutions requires that all the involved parties from the clients up to the contractors share the will to push the boundaries within a reasonable extent. Therefore good teamwork has been essential for the success of the projects shown above: especially the early involvement of the manufacturing companies, as well as the late involvement of the designers during the construction phase has allowed for the intended design to be translated into built reality.