Time factor may affect design choice between fabric and glass

The first retractable sports stadium roof was put on the Toronto Skydome in 1989, and since then designers have gone on to put dozens up around the world. So it is hardly new technology. But adding it to an existing stadium is.

Cardiff's Millennium Stadium has one, designed by HOK Group - which is doing the work for the All England Club. A Canadian company called RWDI is also believed to be working on studies of wind effects inside the roofed stadium.

Though HOK's Alex Mayhew, who is leading the design work, was reluctant to discuss how Centre Court will be retro-fitted with a roof, others have put their minds to it. Roger Ridsill Smith, a structural engineer at the consulting engineers Arup, said that the principal choice would be whether to have a fabric or a glass roof.

Fabric would offer "breathability" (to let moisture evaporate from the grass), but would lose the open-air feeling and would be liable to wear and tear as it was pulled back and forth. Glass is heavier, and not breathable, but is transparent - though Ridsill Smith points out that one has to be wary "in case the spectators bake".

Key factors in the design would be weight and whether supporting the roof would require new columns, which might restrict the view. And there is the time needed to put it up: Wimbledon does have an annual two-weekly commitment. "They could do it in a year, but it would be tight," Ridsill Smith said.

Despite the All England Club's misgivings, there is a precedent to roofing a grass court. The Halle Stadium in Germany hosts a Wimbledon warm-up tournament - on grass - in the same week as the Stella Artois event at Queen's Club. But while the venerable London club has no roof, the German one does: "It was necessary for the success because you can guarantee matches for the TV schedules," the tournament director, Frank Hofen, said earlier this year. "Players know there will be matches played, despite the weather."

Halle has one roof (translucent, rather than transparent) but is considering a second.

Hofen was "surprised" that the All England Club did not put a roof on Court One when it was built in 1997. "It's much more difficult to build a roof afterwards," he said.

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