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The Miami Art Journal

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Stone Exoskeleton Supports London High-Rise Structure

Groupwork and Webb Yates complete Petra Heights using volcanic rock frame

The Editors ·

Stone Exoskeleton Supports London High-Rise Structure

A housing development in north London has been constructed using a structural exoskeleton made entirely of stone, marking a departure from conventional building materials. The project, known as Petra Heights, is located at 317 Finchley Road and comprises three blocks ranging from six to ten storeys in height. The architecture studio Groupwork designed the building in collaboration with the engineering firm Webb Yates.

The structure relies on a thousand tons of volcanic rock to support its weight and resist wind loads. This stone exoskeleton replaces the concrete and steel typically used in high-rise construction. The building features no concrete stability core, no concrete columns, and no steel reinforcement bars. Because the stone serves as both the structural frame and the exterior facade, the project eliminates the need for additional cladding. Steve Webb, co-founder of Webb Yates, described the engineering solution as a world-first, noting that the stone carries all vertical and lateral forces. He stated that without this stone framework, the building would collapse into a pile of rubble.

The materials used in the exoskeleton include Sicilian basalt and Norwegian larvikite. The construction follows a post-and-lintel logic that mirrors the approach taken in Groupwork and Webb Yates’s earlier project, 15 Clerkenwell Close. That previous building, which received a Stirling Prize nomination, also utilized a load-bearing stone exoskeleton but remained shorter at six storeys and retained a concrete core for stability. Petra Heights removes this concrete element entirely, representing an escalation of the earlier design concept. The architects and engineers aim to demonstrate that stone can function as a stable, load-bearing structure for taller buildings.

This project forms part of a fifteen-year initiative by the studios to establish stone as a low-carbon alternative to steel and concrete. The firms argue that these conventional materials account for sixteen percent of global emissions. They posit that load-bearing stone is second only to carbon-sequestering timber in terms of sustainability. According to their calculations, using locally quarried stone can reduce the embodied carbon footprint of a building’s superstructure by up to ninety-five percent. Stone offers a potential advantage over mass timber in the UK, where fire regulations restrict timber use in buildings exceeding eighteen meters in height.

Research conducted by the firms suggests that a similar stone exoskeleton could support a thirty-storey skyscraper. Such a structure could achieve an eighty percent reduction in emissions compared to a steel frame, with no additional cost. Groupwork founder Amin Taha emphasized the sequential use of low-carbon materials, suggesting that architects should prioritize timber and then turn to stone where timber is not viable. The completion of Petra Heights provides a physical example of this material strategy in an urban high-rise context.

Takeaway: Load-bearing stone exoskeletons can eliminate concrete cores and reduce embodied carbon by up to 95 percent if quarried locally.

Source: Dezeen