A geological transformation has taken hold on London’s Finchley Road, where rugged chunks of pink basalt and igneous larvikite appear to have erupted from the railway cutting. These teetering, Flintstones-style towers serve as an unmissable landmark for the Finchley Road and Frognal station, which architect Amin Taha notes is notoriously difficult for commuters to locate. While the city has seen a surge in apartment developments near transit hubs, Petra Heights stands as a radical departure from the standard glass and concrete aesthetic. Anyone trying to find Finchley Road & Frognal station need wonder no more: just look for the multistorey Stonehenge. A result of public transport-oriented policies, but none have looked like the Flintstones were in charge, countless apartment towers have sprouted above London’s stations in recent years. According to “This is one of those stations where people are always scratching their heads trying to find it,”, Architect Amin Taha, standing at the foot of his rocky megalith, an unmissable landmark next to the Overground entrance. “We’re unlikely to start building church spires or grand civic buildings with clocktowers again, so we wanted to make something people could point to and say, ‘It’s next to that building.’”. The igneous rock that holds up these flats has been stacked with deceptive simplicity. You never quite know what the finished result will look like, and the beauty is. If only more clients were so brave. Petra Heights is their biggest proof of concept yet. With chunks of stone bulging out at points in bouldery lumps, it rises above the station platform like an elemental cliff. Which taper as they climb, are connected to a central lift and stairs, and joined by a precipitous bridge at the upper levels, the three towers. The stairway is open to the elements and spills on to a lush communal roof garden, all adding to the feeling of hiking up a rocky mountain path, wrapped with steel mesh. The site went through three different owners before the towers were built, each time seeing the original ambition somewhat diluted as successive developers cashed in on the increased land values, as is not uncommon for developments in London. With stone elements getting chunkier to hold up the additional weight, and braced in places by steel diagonals, that change also had knock-on effects.
Innovative Construction Methods
- Each slab weighs approximately three tonnes, resembling rustic Jenga blocks with visible marks from the drills and saws used at the quarry.
- The three-metre-high, 10cm-thick slabs were sourced from Norway and assembled on-site, with the tower reaching its full height in just one day.
- Unlike standard industry practices that demand perfectly cut materials, Taha embraces the raw, jagged appearance of the rock as it comes from the bedrock, significantly reducing waste and costs.
Constructing a trio of six- to 10-storey towers out of solid stone provides both financial and environmental benefits. Taha highlights that the method is cheaper than conventional steel-framed building and results in roughly 30% fewer carbon emissions. He notes that had the internal frame utilized cross-laminated timber instead of concrete, the carbon savings could have reached 75%. This project builds upon the success of Taha’s Clerkenwell Close development, which gained acclaim for its use of rugged limestone and earned a Stirling prize nomination in 2021. Instead of concrete, as built, it could have saved around 75%, if the internal frame had been made of cross-laminated timber as originally intended. Built from similarly rugged chunks of limestone, stacked with primal relish, which was shortlisted for the Stirling prize in 2021, it follows their striking Clerkenwell Close office and residential project across town. The project had a bumpy ride, originally designed in 2015. As at Clerkenwell, lending it the air of an ancient ruin, the foliage will soon grow its way up the facade. According to the proposed mass timber frame was deemed too expensive, although Taha, The switch to concrete ended up costing much more.
The Vision for a New Stone Age
The project represents a core mission for Taha and engineer Steve Webb: to return structural stone to the forefront of architecture after a century of it being sidelined as mere decorative cladding. Webb is fiercely critical of the construction industry’s reliance on carbon-intensive bricks, which he describes as weak and energy-demanding to manufacture. He argues that modern architecture has reversed the historical logic of building, where walls traditionally supported floors, describing the current practice of floors holding up walls as fundamentally flawed. In the last 10,000 years of building history, he argues, walls have held the floors up. We’ve moved to floors holding the walls up,” he says, “which is utterly stupid, but now we’ve got it back to front. “In the last 50 years or so.
Testing the Future of Design
The duo has pushed their theories further through a “stone demonstrator house” in Earl’s Court, commissioned by the Design Museum’s Future Observatory. This prototype features pre-tensioned stone beams and columns, demonstrating potential carbon savings of up to 90%. Looking ahead, Taha is working on a mixed-use canal development in Hackney that aims to be “carbon negative” by incorporating photovoltaic brise-soleil shading and canal water source heat pumps, with the potential to generate 135% of its energy needs. Creating experimental stone beams, laminated vaults and floor slabs, using pieces of rock that quarries often treat as waste, the duo have become evangelical about the wonders of stone. The pandemic added further setbacks.
Webb is currently exploring load-bearing stone for a 200-metre tower near Liverpool Street, which could eliminate the need for heavy concrete cores.
His firm has even developed a stone pylon prototype, suggesting that the structural properties of stone could be applied to infrastructure. Webb’s firm, Webb Yates, has even developed a slender pylon prototype, exhibited at the Royal Academy, using stone’s stiffness and buckling stability to reduce the amount of steel required.
As Taha notes, “The common reaction from developers is that structural stone is too shocking,” but he remains optimistic that the industry will eventually embrace these methods as a necessary evolution for sustainable development. “It’s a massive opportunity for architects to change it up—a reason to make a new style,” Webb adds, envisioning a future where even electricity pylons are constructed from stone.
