Along with stone plank stands on Store Street in central London, raised on triangular wooden props, giving it the look of a medieval battering ram, ready to lay siege to Tottenham Court Road. This great masonry beam means no harm to the shoppers – but it could well prove to be disruptive in another way.
The slab in question is a prototype chunk of a structural stone floor, an impressively slender thing, 12 metres long and just a few centimetres thick. Cut straight from the quarry and transported to site ready to install, such a floor has a carbon footprint of just 15% of a standard concrete floor – and it’s cheaper, lighter and faster to install.
“Stone,” says architect Amin Taha, “is the great forgotten material of our time. In 99% of cases, it’s cheaper and greener to use stone in a structural way, as opposed to concrete or steel, but we mostly just think of using it for cladding.”
Taha is on a mission to show the potential of stone beyond decoration. Together with stonemason Pierre Bidaud and engineer Steve Webb, he has curated an exhibition at the Building Centre that aims to reveal how this primal material, used to create shelter for millennia, has the potential to revolutionize contemporary construction as we know it. Brace yourselves for the dawn of the New Stone Age.
The architect, engineer and mason have formed in radical stonework. They recently worked together to build 15 Clerkenwell Close, a six-storey block of apartments and an office – including Taha’s home and studio – made from a structure of monolithic stone blocks. The result looks like what might have happened if Mies van der Rohe had been weaned on The Flintstones. It features a load-bearing exoskeleton made of massive chunks of limestone brought straight from the quarry.
The blocks have been left with their raw quarrying marks exposed and stacked on top of each other to form columns and beams. Some of the slabs’ faces show the lines where they were drilled from the rock face, others are sawn smooth as if cut by a cheese wire, while some bear the rugged texture of the sedimentary seam, freshly prised from the Earth’s crust.
The building’s geological power was too much for one Islington councillor, who complained that the “awful” building was out of keeping with the historic neighbourhood, and ensured that a demolition notice was issued, based on a supposed breach of planning permission. Taha finally won the case last year, on the proviso that the smooth stone be roughened up to look like the rest (a process which, after testing, has thankfully proven structurally too risky to carry out).
It seems that the planning battle has only galvanized the trio. They are now determined to spread the gospel of stone, broadcasting their petraphilia to anyone who will listen, with the devotion of geological evangelists.
When you step inside the Building Centre, you are immediately confronted with a large model of a speculative proposal for a 30-storey office tower – designed to be made entirely from stone. It looks like a series of Clerkenwell Closes stacked on top of each other, the chunky stone columns getting progressively thinner as they rise towards the clouds.
“We wanted to prove that a solid stone tower is eminently possible,” says Taha, handing me a substantial technical report that makes a hard-nosed case for such a building on grounds of both cost and carbon footprint. Using stone for the core, structure and floors, they argue, would be 75% cheaper than a steel and concrete structure, and have 95% less embodied carbon. The primary reason for the saving is that, while concrete and steel have to be fireproofed, weathered, insulated, then clad, a stone exoskeleton can be left exposed.
Substituting the stone floor for one made of cross-laminated timber, meanwhile, would make the building carbon negative – so much so, the designers say, that it could offset the embodied carbon of an equivalent tower built of concrete and steel. Images show the craggy stone monolith standing amid the City of London’s cluster of towers, as a welcome contrast to the glassy menagerie of the Gherkin, Cheesegrater and Scalpel.
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