Sports stadiums across the globe are garnering attention for topping off their structures with retractable roofs.
Retractable roof design has come a long way from the Romans drawing the canvas valorium over the Colosseum or the world’s first retractable roof , the stainless steel dome of the Civic Arena in Pittsburgh.
The retractable roof has evolved into a highly engineered structure designed to help moderate climate conditions offering comfort to both spectators and players along with the flexibility for stadiums to host year-round events irrespective of the environment.
For all involved, a retractable stadium roof comes with high expectations. It needs to move into position within minutes with minimal disruption to the game. Then there’s the requirement for weather protection, all the while trying to balance the traditional “outdoor” feel that comes with playing sport and a visually striking design.
However, technology is making all of this very possible and is vastly improving according to Adam Williams, AECOM director of global sports.
Williams, who worked closely on the London 2012 Olympics masterplan and is leading AECOM's work on the Rio 2016 Olympic masterplan, said the more common retractable roofs become, the less risky installing one will be.
“20 years ago, a moving roof to a major stadium was seen as very unusual and risky," he said. "Now it is seen as a relatively standard solution for certain climates and event profiles.”
The last few years have seen Australian capital cities reveal or announce retractable roofs for their stadiums.
Sydney is currently considering a $350 million proposal by BVN Architects to install an polycarbonate operable roof on the already operating ANZ Stadium and return it to a rectangular shape to convert it into a multi-purpose venue that serves different sports.
In Melbourne, Margaret Court Arena will make its debut at the 2015 Australian Open offering continuous tennis play after select games were postponed last year citing extreme heat. Margaret Court is the third sports facility at Melbourne Park to feature a retractable roof.
The Perth Arena which opened late 2012 features a 1,100-tonne operable roof which opens in 11 minutes.
Australia's strong reputation for hosting major sporting events has kept the country invested in implementing the latest technology in sport stadiums with retractable roof installation continuing to rise. Globally, however, there is even greater activity as international sporting tournaments lock in locations years in advance and begin designing for the future.
So when it comes to the retractable roof, it is much more than just a cover. It requires extensive design consideration starting with its environment.
Williams believes retractable roofs are being prompted by two requirements.
“Climate, and the need to host events on as many days of the year as possible to drive revenue and utilisation,” he said. “Clearly these issues overlap: the harsher the climate, the more difficult it is to host certain events because you are susceptible to weather conditions.”
This was evident at the recent 2014 FIFA World Cup Brazil, where temperatures soared and FIFA introduced official water breaks for players during the game.
“Comfort, health and safety of spectators and sportsmen is increasingly a concern in harsh environments,” Williams said. “Risk of player injury increases once temperature on the pitch exceed about 30 Centigrade, and as sports becomes increasingly commercial (and litigious) there is increasing pressure on stadium operators and sporting federations to consider this.”
These types of temperatures are reached in other cities such as Qatar, Doha and Singapore.
For example, Los Angeles architect Daniel Meis has been commissioned for Sports City Stadium for the 2022 Qatar World Cup. It will feature a partially-retractable roof, retractable pitch and a transformable seating bowl. According to Meis' website, "the retractable roof will be large enough to hold people within it, adding to the 46,890 seat occupancy of the stadium," sheltering spectators and a surrounding "village square."
In contrast, BC Place Stadium in Vancouver, Canada has been designed and engineered specifically for the climate and can support up to seven million kilograms of snow.
Williams also outlines the challenges of designing for both these climates prompting the questions:
- How do you clean snow off a lightweight roof?
- How do you stop moving parts clogging up with sand and dust in the Middle East?
Beyond design, robustness and maintenance access is an important consideration to meet these challenges.
When it comes to materials, there is no go-to material for retractable roofs, with the decision being quite complex and again, climate-dependent.
“If you are trying to achieve a fully sealed and conditioned stadium when the roof is closed (i.e. the typical American model) then roofs tend to be heavier and well insulated, especially in cold climates,” Williams said.
Williams added that if the roof is just to be a climate moderating device (shading, preventing wind infiltration), a lightweight solution is more appropriate.
“You need a well insulated roof directly over the stands to reduce heat transfer through the roof radiating onto the people directly below (especially at upper tiers where people are close to the roof), but by the time you get to the part over the pitch, it is basically just sun shade or wind and rain screen, so can be much more lightweight. This is where fabric roofs really come into their own,” he said.
According to Williams, the retractable roof as no longer a stand-alone element but part of a sophisticated climate moderating system. This works in tandem with cooling technologies and other active and passive measures.
“Modern stadia like Singapore Sports Hub use a fraction of the energy to retain a comfortable environment compared with “traditional” air conditioned stadia, which is so much more sustainable,” he said. “Moving roof systems that are AECOM are designing are highly automated; they can be opened and closed in about 10 to 20 minutes using a fully automated remote control centre in the stadium control room. CCTV cameras are deployed across the roof so the operators can see and control everything as it moves.”
Moveable roofs can also be sizeable as engineering firm, Arup demonstrated on Singapore Sports Hub’s 55,000-seat National Stadium. The ultra-thin dome spans 310 metres and is the world’s largest free-span dome.
Like any evolving technology, the retractable roof doesn’t come without its design challenges, including to cost, complexity and maintenance, particularly in sandy regions.
Williams noted a few other challenges retractable roofs pose:
- The moving parts are especially complex compared to normal roof structures. Interaction between the moving and static roofs is often challenging- need to ensure deflections are compatible, for example. Fatigue design can come in for heavier moving roofs. Design for different degrees of openness is essential, as wind profiles and therefore loads can change considerably.
- The partially open state is normally where it is most vulnerable, so careful consideration of operational procedures is required. For example, if it can only open when wind is less than, say, 25 miles per hour, it is important to predict weather before events.
- Choice of materials, especially in the case of fabric roofs. These need membranes that will not damage when folding, for example.
Despite these challenges, stadiums across the globe are experimenting with an array of materials and structural designs.
The retractable roof is only set to rise as cities look to offer perfect playing conditions and maximise the usability of such generous spaces all the while aesthetically looking the part.