'regrow willow' poses hybrid earth construction system strengthened with digital fabrication

digital circular construction with natural materials

ReGrow Willow presents an innovative hybrid material system that combines the tensile strength of willow and the compressive strength of earth for architectural applications. This comprehensive construction process put forth by professorships at the Karlsruhe Institute of Technology (KIT) leverages bespoke digital fabrication processes and computational tools to advance the synergistic combination of the two natural materials. Embracing lightweight, mobile, and adaptable fabrication equipment, and embodying a low-impact philosophy to reduce energy and material consumption, the installation offers a sustainable structural alternative to reinforced concrete.

Championing a circular ethos, the project further seeks to integrate alternative materials and closed-loop systems into construction practices. It presents a potential remedy for resource depletion and waste generation challenges, consequently striving to disrupt the conventional linear economic model of take, make, and dispose. In this way, local material cycles can be closed through waste-free and fully circular digital construction.

all images courtesy of Karlsruhe Institute of Technology (KIT)

Karlsruhe Institute of Technology poses hybrid system

Expanding on previous research conducted by the professorships at Digital Design and Fabrication (DDF) and Design of Structures (DOS) at KIT, ReGrow Willow introduces an innovative resource stream. Willow, a rapidly renewable material, grows up to two meters annually and replenishes yearly after harvesting through short-rotation forestry practices. 

Customized fabrication processes enable the scalability and applicability of such prefabricated building elements, while integrative digital design tools manage the interdependencies between architectural design, material systems, structural performance, and fabrication processes. On the one hand, the resulting components are spatially complex and require advanced design and manufacturing technologies, but on the other hand, their materiality and circular utilization follow simple principles in terms of low energy intensity and recycling opportunities.

The digitally prefabricated components are designed to be reusable thanks to simple, reversible screw connections. Once they have reached the end of their life cycle, the earth, a material that retains its recyclability indefinitely without loss of value, can simply be washed out and repurposed. The willow stems and other natural fiber reinforcement can be composted and returned to the biological cycle, so that these local material cycles can be closed with a waste-free and fully circular digital construction method.

ReGrow Willow research demonstrator at the BUGA Mannheim

willow formwork integrates with the earth

Building with bio-based materials like willow poses challenges due to their inherent variability. Therefore, the project emphasizes the co-evolution of the material system and the fabrication process. A comprehensive fabrication system is developed, starting with a two-axis machine capable of extruding and depositing continuous macro-fibres made from spliced willow stems using additive techniques.

The fabrication process allows the creation of morphologically differentiated components that adapt to the overall design, incorporating adaptive weaving and material placement based on local requirements and structural performance. The earth is shot into selected cells within the willow formwork using a modified plastering machine that employs high-pressure pneumatic extrusion. The geometry of the willow formwork allows for seamless integration with the earth, eliminating the necessity for any additives or adhesives.

digitally prefabricated hybrid willow-earth components

regrow willow imagines a sustainable built future

The ReGrow Willow research demonstrator at the Bundesgartenschau (BUGA) in Mannheim, Germany, demonstrates the possibilities of digitally fabricated willow-earth components. To illustrate a holistic transition to creating a sustainable built environment, it also incorporates concepts of microclimatic adaptation and local energy harvesting. The installation comprises 63 prefabricated components, with weight variations that stem from factors like component dimensions, the earth filling ratio and the specific earth mixture utilized.

The components incorporate a joinery system for inter-component and assembly connections, enabling a fast assembly process completed in three stages, each taking two days. The structure also incorporates design-for-disassembly principles through reversible connections, signifying a shift towards an architecture that can be easily disassembled for potential reuse of its components. Computational workflows inform the material articulation and distribution, prioritizing material efficiency and structural performance, which are also evaluated through physical testing. As a result, a material gradient is achieved, with earth primarily used at the foundations and willow predominating at the top. Two finishing treatments are used to assess weathering impact, an important challenge for earthen construction.

the project incorporates concepts of microclimatic adaptation and local energy harvesting

The willow-earth building system is currently being further developed as horizontally spanning reinforced earth floor slab to showcase the relevance for industrial scalability and its potential for radical reduction of CO2 emissions in large-scale architectural application. The first implementation of this floor slab will be on show at the Landesgartenschau 2024 in Wangen im Allgäu.

championing a circular ethos

the digitally prefabricated components are designed to be reusable thanks to reversible screw connections

the installation offers a sustainable structural alternative to reinforced concrete.

combining the tensile strength of willow and the compressive strength of earth for architectural applications

materiality and system

computational workflows inform the material articulation and distribution

digitally tailored willow rebar baskets before earth filling

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illustration of the digital willow weaving process for prefabricated wicker components

circularity diagram of the willow-earth construction system

integrative digital design process showcased from global design (right) to data-driven structural design (centre) and construction detailing (left)

custom developed digital fabrication equipment for irregular grown materials: digital willow weaving machine

digital fabrication process of willow-earth components

project info:

name: ReGrow Willow
designer: Tenure-Track Prof. Moritz Dörstelmann: Professorship for Digital Design & Fabrication (DDF); Prof. Dr.-Ing. Professor Riccardo La Magna: Professorship Design of Structures (dos); Department of Architecture, Karlsruhe Institute of Technology (KIT)

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edited by: ravail khan | designboom