London Housing Tower Completed With Structural Exoskeleton Made of 1,000 Tonnes of Volcanic Rock

Renters moving into 317 Finchley Road this month are living inside a structural provocation: a 10-storey apartment building held up entirely by 1,000 tonnes of unreinforced volcanic rock. Completed this week by architecture studio Groupwork and engineering firm Webb Yates, the 22-unit Petra Heights development eliminates the concrete stability cores and steel frames that have defined high-rise construction for a century. Instead, the building's weight and the lateral force of London's winds are carried entirely by an external exoskeleton of Sicilian basalt and Norwegian larvikite. For urban residents and developers facing aggressive zero-emission mandates, the project proves that the oldest structural system in architecture can leapfrog the carbon-intensive materials of the modern age, delivering luxury housing with a drastically reduced environmental footprint.[1][2][4]

The complex consists of three stepped blocks rising six, seven, and 10 storeys, wedged onto a constrained site between a railway station and the six-lane Finchley Road. Rather than hanging a decorative stone facade over a hidden steel skeleton, the architects designed a post-and-lintel ladder frame that single-handedly carries the high-rise's structural loads. The assembly relies on 572 distinct stone columns and beams, joined together using steel dowels, brackets, and a minimal application of epoxy mortar. Because the stone acts as both the primary structure and the finished envelope, the building requires no additional cladding.[1][3]

"All of the weight of the building is coming down the stone, and all the wind load is carried by the stone," said Steve Webb, co-founder of Webb Yates, describing the engineering solution as a world first for a building of this height. "If the stone wasn't here, it would be a pile of rubble." The design builds upon the firms' earlier Stirling Prize-shortlisted work at 15 Clerkenwell Close, a six-storey project that still required a concrete core to steady it against lateral wind forces. Petra Heights eliminates that emissions-intensive crutch entirely, relying purely on the geometry and mass of the volcanic rock.[1][2][3]

Sourcing the material exposed the limitations of modern supply chains. Groupwork initially intended to build Petra Heights using local British stone to minimize transport emissions. However, the team was unable to find a domestic quarry capable of extracting blocks large and strong enough for the structural demands, with the largest beams spanning nearly five metres. The architects ultimately imported Sicilian basalt for the lower floors and Norwegian larvikite from the Lundhs quarry for the upper levels, where the tallest block reaches 30 metres above ground.[1][3]

To visually unify the two different types of volcanic rock, Groupwork applied a chemical wash that oxidized the iron content within the stone. The treatment produced a distinctive rusty-red hue that allows the massive exoskeleton to blend sympathetically with the historic red-brick residential architecture of the surrounding north London neighborhood. At street level, the thick stone pillars form a colonnade that shelters a glass-fronted retail space, while the upper storeys are chamfered back to reduce the building's visual mass from protected conservation areas.[1]

Despite the reliance on imported stone and the necessary inclusion of concrete basement foundations and floor slabs, the project achieves significant environmental gains. The architects calculate that the carbon footprint of the materials and construction is approximately 32 percent lower than that of a comparable reinforced-concrete structure. Had the team been able to implement their originally planned stone-and-timber flooring system, the embodied carbon savings would have reached 75 percent.[1][3]

For future buyers and developers, the Finchley Road project serves as a live demonstration of how natural materials can bypass the regulatory hurdles facing mass timber. Under current UK fire safety regulations, the use of structural timber is heavily restricted in residential buildings taller than 18 metres. Volcanic stone carries no such combustibility limitations, allowing architects to pursue low-carbon high-rises without compromising life safety.[1][3]

The engineering team views Petra Heights as an intermediate step in a 15-year research mission to displace steel and concrete, which together account for roughly 16 percent of global carbon emissions. Webb Yates' internal modeling suggests that the unreinforced stone exoskeleton concept could be safely scaled up to support a 30-storey skyscraper. At that height, a load-bearing stone frame could cut emissions by 80 percent compared to a conventional steel structure, without increasing overall construction costs.[1][3][5]

The lessons learned in north London are already shaping the next generation of urban housing. Groupwork and Webb Yates have secured approval for a subsequent residential development in Hackney that aims to push the stone exoskeleton system even further. That upcoming project targets carbon-negative performance by replacing concrete basements with stone foundations and finally realizing the hybrid stone-and-timber flooring system that was sidelined at Petra Heights.[1][3]