New Zealand's transparent, polymer-roofed Forsyth Barr Stadium — the world's only permanently enclosed, natural-turf stadium — has celebrated its first birthday.
The stadium's ethylene tetrafluoroethylene-clad roof is light and translucent, allowing maximum sun- light onto the pitch.
The US$162 million stadium is in Dunedin — the second-largest city on New Zealand's south island. Its rectangular pitch is 433 feet long and 266 feet wide; the internal roof is 121 feet high; and the external roof is 154 feet high. The roof is supported by five arches, each spanning 344 feet.
Construction began in June 2009 and was finished Aug. 1, 2011. It held its inaugural rugby football game six days later, ahead of the 2011 Rugby World Cup, hosted by New Zealand last September.
An international architectural firm, Missouri-based Populous Holdings Inc., designed the stadium with New Zealand-based Jasmax Ltd.
The stadium is the Southern Hemisphere's largest ETFE-covered structure, with 220,660 square feet of ETFE cladding.
Before the stadium was built, turf experts, engineers and architects spent two years studying the effect of grass growing under ETFE. An ETFE test rig was built onsite to monitor grass growth.
Populous associate principal Ron Van Sluijs said grass under the ETFE rig was healthier and stronger than grass around it. “We can maintain a constant temperature and grow a stronger grass which won't become boggy because it will never rain, snow, or hail inside,” he said. “[The] material allows for 90 percent of sunlight to reach the pitch, along with UV light and fresh air.”
Populous associate Jochem Veerman said the plastic roof has performed “incredibly well” in its first year.
“It has a reputation as one of the best playing surfaces in New Zealand. The main benefit of having a roof over the grass is the field's moisture levels can be controlled and are not dependent on the weather,” Veerman said.
ETFE is lighter than glass (just 1 percent of the weight), bears 400 times its own weight and stretches to three times its length, making it suitable for Dunedin's windy, snowy conditions. Van Sluijs and Veerman said the material is up to 70 percent cheaper to install than glass, and transmits more light and heat than glass, reducing energy costs by up to 30 percent.
Van Sluijs and Veerman said polytetrafluoroethylene and PVC are often used for roofing, however neither are as clear as ETFE. They also do not allow sufficient light and ultraviolet rays through. Clear hard plastics, like polycarbonate and acrylic, are not suitable because they have non-UV translucent properties.
They said Forsyth Barr Stadium is not the first to incorporate ETFE, but it is the first time ETFE's UV-transparent properties have been used in a stadium. Auckland's Eden Park Stadium, Munich's Allianz Arena and Beijing's National Aquatics Centre (or Water Cube) also use ETFE.
ETFE-clad, non-sports buildings with vegetation inside include the United Kingdom's Eden Project (the world's largest greenhouse) and the Netherlands' Burgers' Zoo.
Van Sluijs and Veerman said Forsyth Barr Stadium is the world's only permanently covered stadium to house a natural-turf playing field, but is not the first. Houston's Reliant Astrodome was the first, but the grass was replaced with artificial turf within a year after opening.
Some sports venues, like the Netherlands' GelreDome, Japan's Sapporo Dome and Arizona's University of Phoenix Stadium, have natural grass and fixed roofs. However their pitches are on tracks and slide outside the building for growing.
A spokeswoman for Dunedin Venues Management Ltd., Forsyth Barr Stadium's manager, said 350,000 people attended 269 events in the first year.
The stadium can seat 30,000 people.