This immense and glorious Work of fine intelligence!
… These lofty pillars, spread that branching roof
Self-poised, and scooped into ten thousand cells,
Where light and shade repose, where music dwells
Lingering — and wandering on as loth to die;
Design for Living: Gothic ceilings for a low-carbon world
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King's College Chapel, Cambridge.
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Like thoughts whose very sweetness yieldeth proof
That they were born for immortality.
The poet William Wordsworth loved King’s College Chapel at Cambridge University. Who wouldn’t? It’s a masterpiece of Gothic architecture and it has a vaulted ceiling whose beauty and engineering both defy belief. Completed in 1515, its spread-fan shapes are compressed against each other, holding themselves in place without mortar or cement.
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A few years ago the Swiss engineer and architect Philippe Block was so intrigued by this ceiling he climbed on top of it and jumped up and down.
“In thickness-to-span ratio,” he says, “the fans were proportionally as thin as an eggshell. They were so thin I could feel them vibrating. When I jumped, I felt them bounce. And yet they were still strong and standing.”
According to Block, computer models sometimes show that buildings like King’s College Chapel “should have collapsed centuries ago”. But there they are, still standing. “You realise: damn, we have forgotten something. We have forgotten this knowledge.”
Block heads a research institute in Zurich and is trying to get that knowledge back. Not for stone, but for concrete.
As reported last week, every kilogram of concrete emits half a kilogram of carbon. The world is filling up with the stuff and it’s a disaster. What to do? “Green concrete” exists but it’s expensive. Building more with wood will help, but there’s an insurmountable capacity problem: nobody wants to cover the world in plantation forests.
What if concrete could be made like a thin membrane?
Block and his team are focusing on floors, which typically contain about a third of the mass of a high-rise building. As he puts it in engineer-speak, “Providing a flat and horizontal surface for people to walk on is super materially intensive.”
So they’ve developed a flooring system using unreinforced concrete that distributes the forces of compression around the floor, just as the vaults of King’s College Chapel have around that building’s ceiling.
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It uses 65 per cent less concrete and 80 per cent less steel: for a 25-storey building, that’s 1200 fewer trips by the concrete trucks. With no reinforcing steel to degrade, the concrete will last longer. With nothing but compression holding it together, it can be disassembled and reused. The first buildings using the system are underway in Switzerland and Belgium.
Membranous vaulted ceilings have a long history and their newfound value in the climate crisis is not limited to Europe. The technique is common throughout the Islamic world and was used 5000 years ago by the Nubian civilisation in the Nile Valley. “Nubian vaults” are used again today in West Africa, where wood is too scarce and expensive to make framing and rafters for the roofs of houses.
But Block says it’s hard to convince people it works. “We’re so used to thinking: If we add material, it will make things stronger. But geometry is so much more effective at giving you strength and structural stability.”
And as King’s College Chapel proves, beauty too.
Design for Living appears weekly in Canvas magazine.
