- Year : 2013
Photographs :Courtesy of ICD University of Stuttgart
Climate-responsiveness in architecture is typically conceived as a technical function enabled by myriad mechanical and electronic sensing, actuating and regulating devices. In contrast to this superimposition of high-tech equipment on otherwise inert material, nature suggests a fundamentally different, no-tech strategy: In various biological systems the responsive capacity is quite literally ingrained in the material itself. This project employs similar design strategies of physically programming a responsive material system that requires neither extraneous mechanical or electronic controls, nor the supply of external energy. Here material computes form in unison with the environment.
The project explores the tension between an archetypical architectural volume, the box, and a deep, undulating skin imbedding clusters of intricate, climate responsive apertures. The pavilion’s envelope, which is at the same time load-bearing structure and metereosensitive skin, is computationally derived from the elastic bending behaviour of thin plywood sheets. The material’s inherent capacity to form conical surfaces is employed in combination with 7-axis robotic manufacturing processes to construct 28 geometrically unique components housing 1100 humidity responsive apertures.
The apertures respond to relative humidity changes within a range from 30% to 90%, which equals the humidity range from bright sunny to rainy weather in a moderate climate. In direct feedback with the local microclimate the pavilion constantly adjusts its degree of openness and porosity, modulating the light transmission and visual permeability of the envelope. This exchange results in constant fluctuations of enclosure, illumination and interiority of the internal space. The hygroscopic actuation of the surface provides for a unique convergence of environmental and spatial experience; the perception of the delicate, locally varied, and ever changing environmental dynamics is intensified through the subtle and silent movement of the meteorosensitive architectural skin. The changing surface embodies the capacity to sense, actuate and react, all within the material itself.
Biomimetic Principle: Materially-Ingrained Responsiveness
Nature has evolved a great variety of dynamic systems interacting with climatic influences. For architecture, one particularly interesting way is the moisture-driven movement that can be observed in spruce cones. Unlike other plant movements that are produced by active cell pressure changes, this movement takes place through a passive response to humidity changes. Therefore, it does not require any sensory system or motor function. The movement is independent from any metabolic function and hence, it does not consume any energy. Here, the responsive capacity is intrinsic to the material’s hygroscopic behaviour and its own anisotropic characteristics. Anisotropy denotes the directional dependence of a material’s characteristics. Hygroscopicity refers to a substance’s ability to take in moisture from the atmosphere when dry and yield moisture to the atmosphere when wet, thereby maintaining a moisture content in equilibrium with the surrounding relative humidity.
In this way, the movement of spruce cones is rooted in the material’s intrinsic capacity to interact with the external environment, and it shows how a structured tissue can passively respond to environmental stimuli: The cone opening (when dried) and closing (when wetted) is enabled by the bilayered structure of the scales’ material. The outer layer, consisting of parallel, long and densely packed thick-walled cells, hygroscopically reacts to an increase or decrease of relative humidity by expanding or contracting, while the inner layer remains relatively stable. The resultant differential dimensional change of the layers translates into a shape change of the scale, causing the cone’s scales to open or close.
Scientific Development: Humidity Responsive Wood Composites
This project builds on over six years of design research experience investigating the biomimetic principles offered by the spruce cone to develop climate responsive architectural systems that do not require any sensory equipment, motor functions or even operational energy input. The research enables the use of wood, one of the oldest and most common construction materials, as a climate-responsive, natural composite. Wood’s anisotropic dimensional behaviour was exploited in the development of a humidity responsive veneer-composite element based on simple quarter-cut maple veneer. In the process of adsorption and desorption of moisture triggered by ambient humidity changes the distance between the microfibrils in the wood cell tissue changes, resulting in a significant anisotropic change in dimension. Through a precise morphological articulation, this dimensional change can be employed to trigger the shape change of a responsive element.
The developed material can be physically programmed to compute different shapes in response to changes in relative humidity. In this project the elements change from open to closed within a few minutes given a rapid rise in relative humidity. The veneer-composite element instrumentalises the material’s responsive capacity in one surprisingly simple component that is at the same time embedded sensor, no-energy motor and regulating element. The reversibility and reliability of this movement has been tested and verified in a large number of long-term tests, both in controlled laboratory conditions and in outdoor applications. However, it is the first time that the accumulated knowledge has been synthesized for the development of a unique meteorosensitive architectural enclosure for this pavilion.
The project taps into several years of design research on robotic prefabrication, component-based construction and elastically self-forming structures. For this pavilion a computational design process was developed based on the elastic behaviour of thin planar plywood sheets and the material’s related capacity to form conical surfaces. The computational process integrates the material’s capacity to physically compute form in the elastic bending process, the cumulative structure of the resulting building components, the computational detailing of all joints and the generation of the required machine code for the fabrication with a 7-axis industrial robot. Each component consists of a double layered skin, which initially self-forms as conical surfaces and is subsequently joined to produce a sandwich-panel by vacuum pressing. Final form definition on the modular panels, to precise tolerance levels, is achieved through robotic trimming. The structural capacity of the elastically bent skin surfaces allows for a lightweight, yet robust system, constructed from very thin plywood components.
The accuracy of the self-forming process was verified by comprehensive laser scans of the structure. They revealed an average deviation of less than 0.5mm between the computationally derived design model and the actual physical geometry that the material computed in full scale. This not only shows that the integration of material behaviour and design computation is no longer an idealized goal but a feasible proposition. It also demonstrates how focusing the computational design process on material behaviour rather than geometric shape allows for an unfolding of performative capacities and material resourcefulness that expands the design space towards hitherto unexplored architectural possibilities.