“The grass is sacred,” says Populous principal Dale Jennins of the courts at London’s All England Lawn Tennis Club. So when Jennins’ team was designing a retractable roof for the Centre Court, the main stage of the Wimbledon tennis championship, the most important thing to determine was how not to block the sunlight that feeds the world’s most visible patch of grass. The result is a 65-by-75-meter (roughly 213-by-246-foot) hydraulically operated structure of translucent fabric supported by steel trusses. The new roof unfolds across the open stadium should the weather take a turn for the worse during a match.
To determine the proper placement of the roof itself, “it took a couple of years of various computer models,” Jennins says. “It was a two-year process working with our graphic consultants to develop models where the light energy was optimized.” The result was that the aperture for the roof had to be opened slightly.
Once the optimal aperture was calculated, the design team set about integrating the new roof within the existing structure. Built in 1922, the club has undergone many renovations over the years, some more successful than others. The architects wanted to retain the only original façade, the one on the club’s south side. Since most retractable roofs are rigid, and the existing facility was not built to hold such a massive structure, a rigid roof, when open, would create a massive overhang outside the stadium. Thus it became clear very quickly that a collapsible roof system would have to be devised. Railroad-style tracks were installed on either side of the stadium bowl, and giant steel trusses extended across. The roof covering is made from nearly 56,000 square feet of Tenara fabric from Germany’s W.L. Gore & Associates, chosen because of its ability to flex and fold repeatedly without cracking. Most of the time, the roof is parked in the open position, with the trusses stacked tightly together and the fabric folded between. Should weather threaten to delay a high-profile match, the roof deploys, with the trusses moving into place on the tracks, stretching the fabric taut to form a watertight roof.
But in tennis, where the condition of the court or an ill-timed sneeze can make or break a player’s mojo, there were other concerns as well. Moisture on the grass can affect a ball’s bounce, so to keep humidity down when the roof is closed, over 600 air distributors pump dry air into the space—and they do so in perfect silence. To counter the extra noise that an HVAC system makes when it starts up, the team had to work on both the engineering of the system itself and the acoustics of the enclosed space.
The roof was only one part of a six-year project that included the construction of a museum and offices. But should the roof stave off rain delays in this month’s televised broadcast of the championships, it, and not the grass, will be the star of the show.