So, for example, concrete, which has high embodied energy, was used as little as possible; where it was needed, recycled concrete was readily sourced. The wood floor in Jo's café on the second level had a former life at a college in France. Other areas of flooring are made from recycled Heineken bottles and rubber tyres, and the walls are insulated with recycled newspaper.

As the Core is loosely based on the structure of a tree, timber was a must for the frame. Wood - made by the plant from carbon dioxide, water and sunshine - also ticks all of the sustainability boxes as a building material. Sustainably grown and harvested wood with Forestry Stewardship Council certification is now commonplace in construction, but the team made life more challenging as the roof's complex geometry demanded wooden beams that curved not just in one plane but two. Nonetheless, a specialist beam curver using timber with the very best of sustainability credentials was tracked down in Switzerland. Red spruce, grown near the production plant, was the timber of choice.

The big question was the covering for the roof, clearly the Core's most visible and striking external element. "We wanted to cover the roof in a protective shell that would change - like the canopy of leaves on a tree - over time," explains Grimshaw's Jolyon Brewis. "The building will be there for a very long while, so wood was ruled out because it wouldn't have lasted. Slate was too heavy. We needed something with great malleability to cope with the complex structure of the roof.