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Predictably, the design of the Eden Project鈥檚 latest building is anything but predictable. It is called the Core, and it is a 拢15m education centre that was completed in September. Appropriately for an attraction based around plants, the design of its roof was inspired by the Fibonacci series, formed by adding the previous two numbers to make a third (1, 1, 2, 3, 5 and so on). This generates patterns that can be seen throughout the natural world, for example the spiral found in pine cones and sunflowers. The wooden structure of the new building鈥檚 roof is arranged according to this formula.

The windows of the building have also played a part in this mathematical game. Right in the heart of the spiral is a unique, circular rooflight and arranged around this is an array of windows encapsulating photographs of water patterns.

Architect Grimshaw gave Bespoke Glazing Vision, the specialist responsible for the rooflight, a demanding brief. The 5.5 m diameter rooflight had to be flat, yet prevent water pooling on it. It also had three equally spaced spokes that were to intersect halfway along their length to create a triangle in the middle of the rooflight. Finally, the design has to take account of a special, one-off operation that takes place next year. The rooflight has to be capable of being lifted off the building by a crane so an 80-tonne sculpture nicknamed 鈥渢he seed鈥� can be craned into the chamber.

鈥淭ypically an architect comes up with a concept then struggles to find someone to undertake it,鈥� says Ben Snell, Bespoke Glazing Vision鈥檚 managing director. 鈥淭his is what we specialise in. We take a concept, evaluate it to see if it will work and submit our proposals accordingly.鈥� The firm worked with Grimshaw on the solution, produced the detail drawings and finally made the rooflight.

According to Snell, rooflights with conventional framing must have a pitch of at least 15掳 to shed water. Alternatively designers who want a flat rooflight have to use structural glazing and live with water pooling on it. The solution at the Eden Project was to give the rooflight an imperceptible pitch of 3掳 to help shed water. Care had to be taken with the glass selection because thin glass would deflect under its own weight and cause water to pond on it. Selecting the right thickness of glass was a delicate matter because although thicker glass is more rigid it is also heavier and will deflect to some extent, too.

The next problem was how to give the rooflight its distinctive triangular spoke pattern. Originally, the architect wanted the spokes to be made from fins of structural glass, which would not be strong enough if they were attached to the frame at only one end. The glazing designers then suggested strong steel T-sections joined to the glass using structural silicone to create a flush joint. 鈥淪tructurally it was quite a challenge,鈥� says Snell. 鈥淏ut the more bespoke the contract, the more rewarding it is.鈥�

The windows forming a circular array around the central rooflight had to handle a different kind of art. Specialist Fusion Glass Design鈥檚 task was to encapsulate photographs by artist Susan Derges in the windows. The pictures were made by immersing photographic film in liquid then flashing it with powerful lights to capture a variety of watery images. These were digitised and sent to the USA to be printed onto a plastic interlayer.

Turning the artwork into windows was all about teamwork. Rob Robertson, design and creative director at Fusion Glass Designs, says: 鈥淭he main challenge was to translate what the artist was trying to achieve and what the client wanted and put it into glass that performs in the way the architect wants and the building needs.鈥�

The Fusion team made up a set of 500 mm square samples to test whether the picture had come out well and to check for quality. 鈥淟uckily it worked first time. It doesn鈥檛 always translate that easily,鈥� says Robertson. He puts the success down to the water images being monotone and slightly fuzzy, which worked well with the dot matrix effect of the printing process.

Design was the biggest hurdle for both sets of windows. Once a system had been found that met the artist鈥檚 and architect鈥檚 requirements, manufacturing and installation went fairly smoothly. But the rooflight has its final test in six months鈥� time. 鈥淭he big one will be when it鈥檚 lifted off,鈥� says John Richardson, senior at McAlpine Joint Venture, the scheme鈥檚 main contractor. The rooflight will come off in May or June to allow the huge granite sculpture to be lowered into the building. The team are confident that the rooflight鈥檚 big day will go to plan. Until then, it鈥檚 mission nearly accomplished.