Structural Possibilities of Terra Cotta

Terra cotta, or kiln fired clay, has been used for millennia as a structural, finish, and fireproofing material. Spanish building engineer Rafael Guastavino’s self-supporting terra cotta compression arch system, patented in 1892, formed the basis of our initial research.

Additionally, we studied Audels Masons and Builders Guide, published in 1924, and were inspired by the impressive spans achieved by interlocking, hollow-tile arches. This construction system seems to have been largely abandoned by the mid-20th century due to the necessarily tight tolerances that were a challenge to achieve at that time, but which are much simpler to realize today thanks to new building technologies.

We also re-examined Studio Gang’s own past work with terra cotta, including our FDNY Resue Company 2 facility in Brooklyn. Working with Boston Valley Terra Cotta to fabricate its red-glazed details opened our eyes to the complexity and sophistication of the clips and infrastructure required to support contemporary terra cotta façade systems.

Our goal for the ACAW project became to design and fabricate a large-scale terra cotta assembly that reclaims the material’s structural capabilities and light carbon footprint. Working iteratively through design and testing, we developed a pointed arch prototype (named “Archey”) that tests the structural application of tensioning terra cotta pieces into a single, monolithic construction.

Informed by historic assembly methods as well as new technologies, the arch is composed of repetitive terra cotta units that share the same profile. The units are formed via a two-step fabrication process that takes place prior to firing. First, the terra cotta is extruded through a custom, CNC-fabricated die. Second, each piece is robotically wire cut to optimize its structural efficiency and limit excess weight and material. Wire cutting is a low-tech yet highly effective technique for manipulating the extrusion geometry in a third axis. By returning wet terra cotta off-cuts back to the production stream, it also decreases embodied carbon and waste.

To assemble the arch, we rely on the compressive strength of stacked terra cotta units. To tightly interlock with one another they are designed with a grooved top and bottom profile. Temporary falsework is used to support the structure as it is constructed, course by course. To allow for imperfections in the terra cotta pieces, lime mortar is set between each course. The two halves of the arch are then locked into place using high-strength tensioning rope, which runs the length of the arch, threading through integrated voids in each terra cotta element and fastening to custom-made wood feet at the base.

By reintroducing structural terra cotta elements into production and use, our design demonstrates the environmental and functional possibilities of a modular, low-carbon construction system. Completing Archey is a first step in expanding our engagement with terra cotta as a building material that can embody both the ingenuity of the past and a greener, more resilient future.