3D Printing and Robotic Construction: HANNAH Office on their Experimental Prototype Ashen Cabin

Written by Paula Pintos
Published on July 07, 2021

HANNAH office, founded by Leslie Lok and Sasa Zivkovic, is a US-based architecture and research practice that has been experimenting with digital design and fabrication techniques across all types of projects ranging from furniture to urbanism. Both professors at Cornell University College of Architecture, Art, and Planning, Leslie and Sasa lead a studio with a focus on innovative design, where technology plays a crucial role in their work, combined with a sharp study of materials, new applications, and construction techniques, resulting in highly creative projects.

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One of their most recent works is the Ashen Cabin, a robotics-constructed and 3D-printed prototype home in Upstate New York. The singularity of the project lies in the use of infested ash wood, which its abundance is an environmental issue of the area, as it has very few reusable applications at the moment. The use of advanced and custom technology applied in this project has allowed the re-use of this material, which combined with a 3D printed concrete layered structure, resulted in a case study on the future of sustainable construction. Moreover, besides its technological fabrication, the final aesthetics of the cabin remains natural and raw, harmoniously integrated with its context.

We spoke to Leslie and Sasa, from HANNAH Office (HO from now on) to learn more about this project and how they work.

Paula Pintos (ArchDaily) How do you translate the first designs and ideas for the project (“sketches”) into these particular software/tools?

HO: At HANNAH, our process is deliberately hybrid and there exists a lot of feedback between technologies, design strategies, materials, and tools of production. We simultaneously work with sketches, 3D models, physical models, full-scale prototypes, and digital simulations. Each mode of working comes with its own advantages and disadvantages. Together, the various modes of working tend to inform each other – and they also inform us.

PP: How much does technology define your ideas? Or vice versa, how do you make technology work for the desired outcome?

HO: Our projects constitute an interplay between bottom-up processes that are derived from digital fabrication technologies and top-down processes that are derived from our own design biases and from the architectural requirements of a project. On the one hand, we like to play with the rules and constraints of fabrication and we firmly embrace bottom-up logics of fabrication that can be extracted from digital processes. The 3D printed portion of the cabin, for example, adopts the idea of corbelling, an incremental offset of layers to generate three-dimensional form. We play with the toolpath and accentuate the corbelled nature of 3D-printed concrete throughout the cabin’s design. We also embrace the specific geometric rule sets and surface curvatures of the wood envelope, which is also designed from the “bottom-up”. On the other hand, we ask ourselves: “when is it necessary to break those rules”? “When do we deviate from digital efficiencies?” There are ample moments in the cabin where top-down design decisions productively interact with bottom-up logics of digital fabrication: the chimney, the peeling corner window, the ruled-surface roof geometry, the Corbusian drainage scupper, the strangely shaped programmatic concrete protrusions, the entrance door handle, or the awning-looking awning, to name only a few.

PP: Which were the main tools and software used for the project?

HO: For the 3D-printed concrete parts of the cabin, we used Cornell RCL’s (Cornell Robotic Construction Laboratory) self-built 3D printer, called Deadalus. Sasa designed and constructed the printer with his students in 2016 and which HANNAH modified in 2018 to increase the overall printer size to 9x18x9 feet. For the ash wood portion of the building, we used a 15-year old KUKA KR200/2 that RCL purchased from eBay for $8,000. The KUKA robot was hacked and equipped with a large band saw so that it becomes suitable for various types of robotic timber fabrication. The cabin was designed and built by HANNAH, with support from Cornell RCL. We use Rhino for digital modeling and Grasshopper with the KUKA|prc plugin to control the robot.

PP: Is the raw and rustic aesthetics of the materials a conscious search in favor of more natural and expressive architecture, or is it simply the result of the methods and technologies involved?

HO: In the case of the Ashen Cabin, the raw nature of the materials is a pragmatic manifestation of the fabrication processes and material used. We embraced the corbelled and striated nature of the 3D-printed concrete, with all its imperfections. The horizontal lines are simply the result of the fabrication process, similar to the patterns that result from board-formed concrete.

For the wood envelope, we had a similar approach. The envelope is constructed using wood from trees that are infested by the Emerald Ash Borer, which threatens to eradicate (is in the process to eradicate) billions of ash trees in North America. This is a huge environmental problem and concern. We wanted to use robotic fabrication technology and 3D scanning to utilize ash wood that cannot normally be used for construction because of its irregular geometries. With this particular technology, there is no need to ‘square-off’ a log, which is why we decided to retain all the live edges of the wood. The resulting wood envelope expresses an interplay between natural/organic materials and a highly precise fabrication process. The whole cabin operates within this techno-organic narrative.

PP: The concept of “tectonic articulations” is especially interesting because 3D printing technologies usually work by building on the addition of a single composite material. Can you tell us more about this concept and explain how you have managed to design and generate these “connecting pieces” between materials?

HO: There are two main tectonic systems at play in the cabin, the 3D printed concrete and the wooden envelope. We purposely designed the cabin as a hybrid material system so that we can generate spatial and tectonic complexities in the interplay between systems. The 3D-printed legs and base, for example, are expressed as individual components throughout the connecting slab, which breaks down the volume of the concrete and emphasizes a transition from horizontal to vertical systems: all concrete is striated horizontally, according to the construction logic of 3D printing, while the wood is striated vertically, to create differentiation between the systems, referencing traditional barn construction techniques in the area. Individually, the systems express tectonic logic in more nuanced ways. The ornamentation of the 3D printed concrete floor, for example, is another direct result and expression of the fabrication process. In the wood façade, for example, the door surface gently peels outward to create an oversized door handle. In addition to the main systems, the ash wood and 3D-printed concrete, we also use “regular” materials such as plywood for the black window frames or timber joists for the ruled surface roof.

3D Printing and Robotic Construction: HANNAH Office on their Experimental Prototype Ashen Cabin - Image 26 of 26 — © Andy Chen

PP: Can you tell us more about high-precision 3D scanning-based fabrication technology and its role in this specific project?

HO: 10 EAB-infested ash trees with their natural geometries were used in the construction of the Ashen Cabin. We used a cross-section of typical ash trees from the Cornell Arnot Forest, some of which were straight and some of which were curved. Our research team used handheld scanners to generate a digital version of all the logs, which we were then used to calibrate our initial designs based on the available materials and geometries. Once this initial design process was completed, we used 3D scanning to index the logs that were mounted in front of the robot for fabrication. After being 3D scanned in place, we adjusted the cutting tool path for the robot, matching the digital model with physical reality. 3D scanning enables us to precisely cut and process irregular log geometries with robotic equipment.

3D Printing and Robotic Construction: HANNAH Office on their Experimental Prototype Ashen Cabin - Image 11 of 26 — Courtesy of HANNAH

3D Printing and Robotic Construction: HANNAH Office on their Experimental Prototype Ashen Cabin - Image 10 of 26 — © Andy Chen

PP: How long did the construction of the house take and what positive benefits do you recognize when comparing it with the construction of a similar traditional house?

HO: It took us two summers to design and build Ashen Cabin with the help of a dedicated team. The first summer, in 2017, we prepared the construction site and then went on to design and construct the concrete portion of the cabin. In the summer of 2019, we designed and constructed a wooden envelope for the cabin. Ashen Cabin is a prototype and we are not professional builders, which makes it difficult to compare the project to the construction of a regular house. However, we do believe that the project’s prototypical systems are potentially scalable. Ashen Cabin offers one possible solution to address the ecological problem caused by the Emerald Ash Borer infestation and charts a unique path for the integration of design, sustainability, and new technology.

This article is part of the ArchDaily Topic: Automation in Architecture. Every month we explore a topic in-depth through articles, interviews, news, and projects. Learn more about our monthly topics. As always, at ArchDaily we welcome the contributions of our readers; if you want to submit an article or project, contact us.