Recent Adaptive Textile Façade Systems

1 Introduction

The building sector stands for more than the fifty percent of human resource consumption, causes the emission of more than 38% of man-made greenhouse gases (GHG) [1], and generates more than half of world-wide waste [2]. The Collaborative Research Centre (CRC) 1244 “Adaptive Skins and Structures for the Built Environment of Tomorrow” at the University of Stuttgart has been working since 2017 on the question of how the ecological footprint of the built environment can be drastically reduced. Adaptive structures and facades are one of the most promising answers to varying environmental conditions and user needs, as well as to the need for more resilience in architecture. A façade whose properties remain almost unchanged - no matter which is the inside or outside temperature, the level of sun radiation or the user requirements to be dealt with – cannot match the claim for more resource efficiency and climate adaptation. New design strategies and technologies must be developed and experimentally validated. This is the target of the interdisciplinary research group in Stuttgart: it comprises architects as well as structural, mechanical, control engineers and computer scientists.

The first research phase (2017-2020) focused primarily on design and control methods for adaptive structures. As a result, a circa 36.5 m tall demonstrator adaptive high-rise was designed and built. The tower, called D1244, was completed in 2021 [3]. The structure is equipped with twenty-four hydraulic actuators that are installed in the columns and diagonal bracings. A life cycle analysis (LCA) supported the different design phases [4] with the aim of testing the environmental impact of the different solutions envisioned. D1244 is not only an ideal framework to test and showcase the developed technologies; it is also a modular and flexible experimental platform. Each structural and façade component can be replaced over time, to test new components developed within the frame of the CRC 1244. The demonstrator thus also serves to develop and validate methods and processes for the design of adaptive buildings ([5, 6, 7]).

Figure 1: Experimental adaptive tower D1244, University of Stuttgart © R. Müller

Since 2021 the focus of the design and development of adaptive components has shifted towards the development of adaptive facades. Every floor is planned to showcase different adaptive functions or technologies. Following up on the installation of HydroSKIN prototypes at the tenth floor in 2022 [8,9], this paper focuses on two new façade systems, which were recently installed at the ground floor of D1244 (FiberSKIN and MagneticSKIN). It also describes the canopy installed above the ground floor and provides up-to-date information on the textile kinetic shading solution under construction at the second floor (KineticSKIN). The façade “wings” to be installed here respond to different daylighting conditions and aim at reducing heat island effects in urban environments.

Figure 2: D1244, facade transformations 2022-2024 and conceptual rendering of the top floors © H. Schürmann / ILEK

The gradual replacement of the temporary skin allows also for experimenting ways of disassembling and upgrading buildings (see Fig. 2). This goes beyond the general understanding of adaptive systems: therefore, the research group rather uses the term adaptability [10]. As a proof of concept, the tower is to be transformed over the years not only through an exchange of components but also thanks to carefully designed extensions.

2 FiberSKIN

2.1 Design

The idea underlying the design of FiberSKIN is that of a moving “veil”, which protects the hydraulic structural system of D1244 at the inside while allowing for a visual interaction with the surrounding platform area, where events and various activities take place. An interdisciplinary team of architects, structural engineers, and mechanical engineers came up with a customized screen made of lightweight and fully recyclable glass and basalt fibers [11]. The project was also a methodological test to validate early interdisciplinary collaborations in the field of adaptive facades [7]. A close cooperation of the designers with the panel manufacturers, Sailmaker International with their i-Mesh technology, allowed for a highly customized solution, especially in the optimization of the fiber pattern. Beyond the realm of D1244, the developed solution has a potential application for building skins where no thermal insulation is required, and where façade panels have to be lightweight and, eventually, movable.

Figure 3: FiberSKIN Façade at the south corner of D1244 in May 2023 © M. Jeong / ILEK

Featuring the integration of lightweight textiles and a double-sliding mechanism, FiberSKIN blends the conventional notions of curtain wall and curtain (see Figure 3): it prevents not only water penetration into the interior but also regulates light transmission while generating special visual effects. The fiber panels cover three sides of the ground floor: two fixed panels clad the southwest and northeast sides, while two layers of movable panels clad the southeast side. The panel design is based on a geometric pattern radiating from intentionally placed clamping points (see Figure 6). The number of clamping points differs depending on the function of the panels: the two 5.2m wide movable panels are clamped with 12 nodes to glide smoothly along the curved corners, while the 6.6m long fixed panels only need half of the nodes to withstand wind forces (see Figure 4). To achieve a consistent pattern across all sides, a geometric rule is applied. This rule affects the pattern parametrically in response to variations in distance between nodes. The resulting pattern design leads to an extraordinary spatial experience indoors and outdoors based on the way the sun hit the panels and the shadows are cast.

Figure 4: View through the SW fixed panel from inside D1244 © M. Jeong /ILEK

A color scheme inspired by the constituent materials of the fibers (basalt and glass) has been laid out to enhance the symbolic level of the design, as explained in the following. In the fixed panels the basalt fibers are concentrated in the bottom part. They generate a metaphorical and optical link to the ground and to the earth, given their volcanic origin. Meanwhile, glass fibers placed primarily at the top of the fixed panel transmit considerably more light. They are used to create a link to the sky. In the moving panel the two material constituents are made visible in a different way since two panels overlap in the closed position: the front panel is made entirely out of glass fibers, the back panel is made entirely out of basalt fibers.

2.2 Kinetic Concept and Mechanical Implementation

Various methods were applied to develop the kinetic concept for a flexible screen to be fully opened at the front side of the tower: especially the “brainwriting” and the “gallery” methods [12] supported the investigation of more than 20 different opening concepts. These included simple openings such as theater curtains but also complex movement patterns. The concepts generated were then evaluated and selected based on various factors such as their respective architectural quality and ease of implementation. The method finally chosen was a double sliding mechanism.

To implement the mechanical structure, several references were studied. Sailboats, garage doors, and conveyor systems have similar properties and potentially allow for a transfer of know-how. To gain an insight into the design and construction as well as the special features, manufacturers and experts were contacted. In the end, the mechanical system chosen was most similar – due to the intended movement – to side sectional garage doors. A collaboration with one of the leading manufacturers in this sector, Hörmann KG, was started: cyclic tests combining modified industrial products in combination with samples of the designed textile façade were carried out.

The CAD model for the substructure of FiberSKIN is depicted in Figure 5. One challenge in designing the façade was the transition from tolerances between the structure of the building (some cm) to the façade (a few mm). To achieve this, two specially designed support structures were integrated into the design. The first one is shown in Figure 5 in the right upper corner. The sheet-metal design was selected as it matches the overall lightweight design. Here, another industry partner (TRUMPF Werkzeugmaschinen SE + Co. KG) supported the design and manufacturing of the brackets. In general, the collaboration with industrial partners helped not only to optimize the prototype costs but also expedited technology transfer in both directions.

Figure 5: Functional substructure of the façade (left) with detail view on support structure bracket (right) © M. Voigt /IKTD

The detailing focus was set on the clamps and on the large brackets that hold the facade. The clamps, which were placed regularly along the facade, served as an interface between the mechanical and architectural components. These are an integral part of the kinetic mechanism and fix the textile through special keder connections. Figure 6 visualizes the different development stages.

Figure 6: Design process of the keder clamp – optimizing shape, weight, and functionality © M. Voigt / IKTD

3 MagneticSKIN

In contemporary architectural practice, there is a growing emphasis on the ability to tailor specific properties of building envelopes to enhance comfort and overall space usability [13]. This focus primarily revolves around meeting physiological needs and individual preferences. However, the exploration of psychological needs and the broader activation of human senses remains largely uncharted territory. The proposed system delves into the significance of bridging this gap and investigates the potential benefits of integrating sensory stimuli to create more engaging and immersive built environments, within a user-centric design approach.

3.1 Concept

MagneticSKIN is an interactive facade system designed to respond dynamically to human touch (see Figure 7). By exploring non-verbal ways of communication through haptic interaction, this approach aims to create a harmonious interplay between architectural aesthetics and human experience. “Touch is the sensory mode that integrates our experience of the world with that of ourselves” according to Juhani Pallasmaa [14]. Architects can enhance the emotional connection people have with their surroundings, integrating touch and other sensory experiences in the design concept. The ground level of D1244 is ideal for this purpose since it offers direct and convenient accessibility for individuals to engage with both the external and internal layers of the system. The outer façade measures approx. 2900 mm in height and 6200 mm in width.

Figure 7: Live interaction with the MagneticSKIN facade during the CRC 1244 symposium in May 2023 © U. Regenscheit.

The interaction system follows some of the basic principles of system dynamics otherwise used in D1244: it comprises a set of sensors and actuators interconnected through a micro-controller and a specific set of rules or code. The overall technological set-up therefore matches the core of the cooperative research center; however, the field of application is expanded from a traditional performance driven design to an interaction driven approach. The intent is to improve the acceptance of new technologies by engaging haptic experiences and the resulting perceptions in a non-conventional way.

The outer membrane functions not just as a protective medium between the exterior and the interior, but mainly acts as an interface for the multiple interaction scenarios. The 1500 x 2060 mm internal textile layer is designed to enhance the overall experience, enabling users to imagine a non-visual, haptic interaction that transcends the known boundaries between external and internal environments. The further development envisioned for this system involves the two layers acting as one unified system, with consistent responsiveness regardless of the users’ spatial positioning.

3.2 Pattern design and detailing

The arrangement of magnets on the membrane surface follows a deliberate pattern inspired by the key trigger points found in an average-sized human hand. The abstract representation of these points results in a group of eight round magnets. There is a total of five variations of this group, out of which the overall semi-regular clustered pattern is created by organically arranging them across the canvas. Two exemplary arrangements and the basic development of a semi regular clustered pattern are depicted in Figure 8.

Figure 8: Pattern creation based on trigger points inside a human hand combined with spatial point arrangements © A. Cazan/ILEK.

The neodymium magnets measure 15 mm in diameter and vary in thickness from 1,5 mm (inner layer) up to 3 mm (outer layer). Each group of eight magnets corresponds to an electromagnet and sensor, working together to form what is referred to as an active module. In addition to the active modules, there are “passive modules” composed of either individual permanent magnets or groups of magnets, to which no actuator is assigned. The role of these passive modules is to complete the pattern, especially in areas not easily reachable by hand. By placing one magnet on the inside and one on the outside of the membrane, the connection is made solely by the electromagnetic field, thus also allowing for easy reconfiguration and disassembly.

Figure 9: Haptic interaction with the inner layer of MagneticSKIN (left) interaction system seen from the inside (right) © A.Cazan/ILEK

3.3 System functioning and first feed-backs

The name MagneticSKIN derives from the use of electromagnetic properties to activate the double-layer textile skin. 24 V powered electromagnets, each capable of generating an attraction force of 800 N, serve as actuators. By placing permanent magnets on the membrane, the electromagnets behind the membrane can attract and repel the latter at predefined time intervals, thereby creating a pulse-like sensation on the surface. The intensity of the effect directly correlates with the number of activation points perceived by the ultrasonic sensors and the depth of the inward movement. The greater the number of activated points, the more intense the overall effect, which can be seen and (more importantly) also be felt by the users interacting with the facade.

When touching the inside or outside of the facade, users push that specific area of the textile back toward the core of the system, thus triggering the interaction. This inward movement is continuously monitored by ultrasonic sensors, which measure the distance to the default state of the membrane. For each actuator in the system there is a corresponding sensor which transmits the received information to the Arduino micro-controller, which in turn processes the data and activates the corresponding actuators until the predefined conditions stipulated in the code are met (Figure 9 right). Distance and time are the defining parameters in reaching the desired effect. By experimenting with the time intervals between activations, changes in polarity, and the natural vibration frequency of the membrane, different pulsation rhythms can be achieved.

Since its installation in May 2023, the system has offered visitors a dynamic interface for exploring haptic interactions. The feedback has been very positive so far, with many describing a pulse-like sensation similar to a heartbeat and expressing a willingness to engage with it, thus validating the design intention. Having observed the system in use, it can be stated that incorporating interactive elements in the facade design encourages user engagement and instills a sense of “ownership” over the building. This is a significant step forward in understanding the potential of haptic communication in architecture, paving the way for the creation of more immersive and user-oriented built environments.

4 CANOPY

The lightweight canopy of the ground floor is an architectural element designed to seamlessly integrate the facades at the ground floor with the shading systems developed for the second floor of D1244. The canopy harmonizes the specific character and morphology of the different textile skins: it highlights the access to the tower with its rounded corner at the front and it follows the orthogonal corners of the MagneticSKIN on the back side (see Figure 10). Moreover, it shapes the transition between the skins at the ground and second floors. This way a coherent visual language throughout the tower base is ensured.

Figure 10: D1244 Canopy: Creating constructive interaction among different skins © J. Lopez /ILEK

Functionally, the canopy protects against harsh weather, mitigating the impact of rain; it filters sunlight in summer and allows for insolation of the interior in winter. The membrane used was chosen not only because of its optimal level of translucency but also because it is produced out of recycled plastic bottles (rPET polyester). This way it is shown how the use of primary resources and the overall ecological footprint can be reduced without affecting the architectural quality of a design.

Figure 11: D1244 Canopy: Integrated BIM Model © J. Lopez /ILEK

5 KineticSKIN

KineticSKIN is an innovative adaptive kinetic facade designed to dynamically adjust its components’ position in response to seasonal changes and user preferences. Its primary objective is to harness solar radiation effectively, enhancing visual comfort and optimizing building energy cycles [15, 16]. This is achieved by strategically redirecting solar radiation to improve indoor daylighting conditions and minimize incident solar radiation in urban canyons [17]. The experimental façade is a double-skin made up of an inner layer of curtain wall glazing units and an outer layer of KineticSKIN modules. Each module consists of an upper and lower wing; a cluster of 12 modules has a shared control system for the upper and lower wings respectively. A total of 3 clusters makes up one façade side. The entire system will be installed on the second floor of D1244 on both south-east and north-west sides until mid of 2025 (see Figure 12).

Figure 12: Vision of KineticSKIN on D1244 © M. Jeong / ILEK

By adjusting the position of wings through changes in folding angles, incident solar radiation is strategically redirected. The upper wings address seasonal variations: in summer, they track the sun's position to block the solar radiation, thus reducing cooling demand and mitigating excess solar heat in urban areas. Conversely, in winter, the upper wings reorient solar radiation towards indoor ceilings, optimizing interior natural lighting while minimizing glare. The lower wings are user-controlled, allowing users to customize indoor conditions to meet specific requirements for illuminance levels and ventilation. Ensuring stability for both actuation and external loads, the wings are supported by two cables—one on the backside for actuation and the other on the frontside to counter weather loads. An integrative design approach brought together a team of mechanical, control, and architectural engineers to design KineticSKIN following lightweight construction principles: the overall target was to balance the system’s aesthetical qualities with its performance and sustainability. Operational efficiency is for instance improved by optimizing the number of actuators, reducing weight and energy consumption.

Figure 13: Installation of glazing units on the second level of D1244 in November 2023 following disassembly of the temporary facade © M. Jeong/ILEK

The engineering and construction of the curtain wall glazing were carried out by Josef Gartner GmbH in November 2023 (see Figure 13). The glass façade, spanning 6 m on both the southeast and northwest sides where the façade module are installed, is vertically divided into three sections. The glass specifications feature a thermal transmittance (U-value) of 1 W/m²K, suitable for office buildings, and a visual transmittance (Tvis) of 50%. On the sides where KineticSKIN modules are installed, three fin brackets are embedded in the mullions at the top, middle, and bottom, designed for the installation of façade modules at a later stage. The prototype of the shading system is currently in preparation: the first performance mock-up is scheduled for installation in the summer of 2024. Consequently, a real-world assessment of the impact of the system under varying conditions will be started in the second half of 2024.

6 Conclusion and outlook

The three façade systems described in the present article as well as the HydroSKIN prototype already installed in 2022 [8] show the high range of functionalities which can be achieved by using textile skin systems for a more adaptive architecture. Due to their lightweight and flexibility, it is easy to move and deform such panels. This fits very well with the attempt of designing innovative adaptive systems, reacting to different conditions in a dynamic and effective way. Modern textile skins can be also designed, manufactured and built in such a way that each component has a low carbon footprint and is fully recyclable. Moreover, embracing interactive technologies and haptic qualities of the materials could give architects the opportunity to create immersive experiences, where architecture transcends its traditional role and becomes a dynamic medium for human interaction and sensory perception.

Moreover, the experimental interdisciplinary setup of the CRC 1244 allows not only to explore the potential of new systems, geometries, and functions, but also to validate the developments in a real-world condition and showcase the quality of the application in full scale (see Figure 14). Within three to four years all 12 floors of D1244 will be clad with different adaptive façade systems. The next focus (until the end of 2024) will be on insulated glass units, integrating further functions such as cooling (CoolSKIN), smart glass control and energy harvesting (SmartSKIN at level 12), etc. (see Figure 2). As soon as all façades are installed, the next cycle will start, thus establishing D1244’s character as a full-scale and long-term experimental and dynamic laboratory. 

Figure 14: D1244: Current status of the façade installation in December 2023 © M. Jeong / ILEK

At every step the process of disassembly and assembly is being optimized. The critical analysis of the conversion work carried out at the ground floor façade provided the first information how design and implementation processes could be further improved [10]: among others there is a need to improve some aspects of the design process and to further develop the interface details, used to exchange building components over time. As per our experience, adaptation scenarios must already be documented in the design phase with as much detail as possible; moreover, the interfaces must be tested more intensively in advance. The possibility of integrating "predetermined breaking points" into buildings is one of the resulting fields of research: at those predefined interfaces, building components or even full levels can be added or removed in a precisely planned and documented process. As a result, there is a need for further research into joint types, their non-destructive disassembly and adaptability since well-designed connections and reliable interfaces are essential for the functioning of adaptable construction.

This opens a field of research which goes beyond the classical field of adaptive technologies and has a relevance for a wider set of buildings. These are the related questions: how can existing buildings be extended in a sustainable manner? How can new buildings be constructed in such a way that they remain adaptable in the long term and are therefore used over longer time spans? How can we raise the circular character of our design and manufacturing processes? The overall target behind these questions remains the same: reducing consumption of natural resources, waste generation and climate changing emissions. As a result, in the future D1244 will work not only as an experimental tower to implement and validate several adaptive facade technologies but also as a real scale laboratory to address the questions of improving adaptability in the built environment.

The research work of CRC 1244 is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 279064222 – SFB 1244. The four projects described in the present paper have been made possible through the research work of different interdisciplinary teams and thanks to the support of several industrial partners and the engagement of the ILEK technicians (T. Tronsberg and M. Berndt). The authors would like to express their gratitude for this support.

FiberSKIN Team: M. Jeong, L. Blandini, H. Schürmann, M. Matheou (ILEK) /
M. Voigt, D. Roth (IKTD)

FiberSKIN Partners: Sailmaker International (i-Mesh), Hörmann KG
Verkaufsgesellschaft, TRUMPF Werkzeugmaschinen SE+Co. KG

MagneticSKIN Team: A. Cazan, H. Raisch, F. Kokud, L. Blandini (ILEK)
MagneticSKIN Partners: Roho GmbH, Koch Membranen GmbH, Mehler-Texnologies GmbH

KineticSKIN Team: M. Jeong, M. Matheou, L. Blandini (ILEK)
KineticSKIN Partners: Josef Gartner GmbH

Canopy Team: J. Lopez, L. Blandini (ILEK)
Canopy Partners: Richter Lighting Technologies

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