Adaptive Facades

Facade engineering aims at appropriately balancing the demands imposed by the context and the capabilities inherent to the materials, the geometries and the systems that are implemented. Traditionally, systems are designed for the worst case conditions, thus leading to static designs that are over-dimensioned for most of their service life. Therefore, if a system - just like a living body - is able to adapt itself to the external conditions by changing its properties, then it would bring about a new design paradigm that can lead to substantial savings and that can enhance the performance of the building.

Numerous researches, prototypes, and components have been carried out so far, and projects, both speculative and realized, are imagining the application of such systems on an architectural scale, in order to exploit their viable potential and redefine the premises on which the development of the built environment is set.

In this light, examples like the visionary proposal for house R129 (Sobek, 2001), where the transparent shell complemented with an electrochromatic foil enables the building to dynamically respond to the changing conditions of its context, or the Cité du Design in St. Etienne (Geipel and Andi, 2004), where the skin adapts to the interior requirements, have shaped this novel approach to envelope design and fueled the dialogue around the concept of adaptivity.

In this process, research institutions play a crucial role; indeed, through the promotion of studies and researches, innovative systems and methodologies are developed, thus fostering a continuous progress in the building sector, from a design as well as a manufacturing standpoint.

Among the researches currently carried out, this paper aims at presenting in particular two prototypes, developed at the Institute for Lightweight Structures and Conceptual Design (ILEK) in Stuttgart, which address the concept of adaptability with regards to two crucial performances and that introduce two influential references for the design and engineering of future transparent skins.

The first prototype, Research Project A, involves an adaptive glazed facade with vertically prestressed cables, where, by means of actuators, the active components, weaving together the double cables and changing their reciprocal distance, modulate the prestress forces and the curvature of the cables, according to the present loading condition measured by sensors, and optimize the structural behavior of the facade. The results show that - compared to a standard cable construction - the adaptive cables system can lead to a striking minimization of the members sizes and, as a consequence, of the material usage.

Research project A has been carried out by Christine Flaig (ILEK - University of Stuttgart), Dr. Walter Haase (ILEK - University of Stuttgart) and Michael Heidingsfeld (ISYS - University of Stuttgart) within the framework of the Research Group 981 (HIKE) funded by the German Research Foundation (DFG).

The second project, Research Project B, consists of a switchable glazing unit with adjustable light and energy transmission properties. While current switchable glass technologies feature long respond times and rough subdivision of the glazing area, the prototype developed enables substructured control and grey scale states, thus allowing a precise modulation of the daylighting and energy performances, without compromising the visual comfort. Ultimately, by linking together the data from the sun and the test room, an initial automated and dynamic control strategy has been implemented.

Research project B has been realized by Marzena Husser (ILEK - University of Stuttgart) and Dr. Walter Haase (ILEK - University of Stuttgart), supported by the Federal Institute for Research on Building, Urban Affairs and Spatial Development within the Federal Office for Building and Regional Planning, Germany (research projects: “Adaptive glazing systems”, “TN technology for architectural applications”) and by Baden-Württemberg Stiftung GmbH, Germany (research project: “i³: intelligent, interactive, integrative solar control glazing”).