How to add a roof

Stadium roof design is advancing to the extent that they can now be incorporated into existing facilities

Self-sustainability is the watchword for making sure a stadium has a long and profitable lifespan. For some stadium managers, this means using space in more efficient ways. Others may opt to use the premises more often and for more diverse events.

Most stadium managers would like to increase revenue by opening up around the clock and all year round, in heavy rain or blinding sunshine. They also want to improve comfort for spectators, who will bring in more and more revenue as they return for future events. And managers want to provide protection from the elements and to prevent noise from being spread over the neighbourhood.

The Red Bull Arena in Salzburg, Austria, opted for heated
artificial grass field instead of a roof

A roof over a stadium makes all these things possible. Little wonder then that most stadium managers would now prefer to have a roof over their facility. But stadiums are complex designs that, once built, leave little space for radical adjustments. Once a stadium has been built, it is extremely difficult to make drastic changes to the structure.

Arches and columns
To overcome this major obstacle, Jaap van Nunen and Bas Verhoeven, engineering researchers at Avans University in Tilburg, The Netherlands, devised a way of customising large, existing sports facilities with new coverings. “The design was developed around the idea of covering large areas with a roof-supporting construction,” Jaap van Nunen says.

They focused their attention on how best to modify existing constructions. Their design incorporates arches that cover the roof of the stands on the side-line of the pitch. These arches are fixed on columns in the corners of the stadium. The field is covered by layers of flexible, transparent panels, mounted between beams.

The challenge was to design a construction strong enough to cover a large area and withstand the elements. The design also met another important criterion, which was to support itself without any connection with the existing structure. Van Nunen says: “This allows us to meet the 27m height that is required by the world governing body for football associations, FIFA, without any problem.”
 
Nurturing grass growth
On top of this, the engineers had to consider the requirements necessary to create proper grass growth. Grass needs water, light and oxygen; the better the access to these requirements, the better the quality of the pitch. Since natural turf is used as a surface for most stadiums, it was critical that the design posed no permanent obstruction to rain, air and sunlight.

Van Nunen and Verhoeven considered three options: the use of a fabric that can be moved away; a moveable system supported by sleepers hanging below the arches; and rotating panels, similar to the systems used on buildings to prevent offices from sun light. They decided to go for the final option.

Opening the rotating panels allows rain, light and oxygen coming into the stadium. Using translucent panels also ensures that enough sunlight reaches the pitch.

The advantage of this chosen system is that panels can be rotated without affecting the construction. This makes maintenance easier, while contributing to the stability and safety of the stadium. In the event of a fire, the panels can be opened quickly to release smoke.

Under pressure
Roofing an area of at leat 7000 sq m generates huge pressures on the construction, both from the roof itself and from the elements. “A roof must be able to resist permanent and variable pressure,” Verhoeven says. “Permanent pressure is already in the construction but the variable pressure differs all the time. Snow and wind are examples of that.”

The Commerzbank Arena in Frankfurt has a non-translucent
fabric roof which allows for quick opening and closing

The engineers calculated the maximum expansion of the building materials under the influence of warmth or heat and incorporated this into the structure. The construction also allows people to walk over the roof, which is a requirement of maintenance. By designing the roof in an arch, the structure is tailored to withstand these large pressures and changes.

The design is, in essence, a much lighter construction than those used in conventional retraceable roof stadiums like the Amsterdam Arena in the Netherlands – or Miller Park in Milwaulkee, US. The roof of Miller Park is designed in a fan shape, with each of five movable sections pivoted at the home-plate end and riding on two bogies at its wide, outfield end 183 metres away. Weighing in at 12,000 tonnes, this roof heaps great pressure on the stadium’s structure.

The engineer behind Gelredome stadium in the Netherlands, which has a retractable roof, says van Nunen and Verhoeven’s design has major potential benefits. “Roofs for stadiums are very heavy, making it virtually impossible to construct them for existing stadiums. This system could work much better.”

Solutions are available
To work out how to implement their plans to roof an existing stadium, van Nunen and Verhoeven used the Rat Verlegh stadium in Breda, The Netherlands, as a case study. The stadium, named after Antoon “Rat” Verlegh, a former player, volunteer, trainer and board member, was built with the intention of building a second tier in the near future. It already has a field reinforced with artificial grass.

“We have calculated the investment and exploitation budget and studied the feasibility of the project. Based on the calculations we believe it is achievable for stadiums like the Rat Verlegh stadium to get a roof constructed like we have designed,” van Nunen says.

The Rat Verlegh’s facility manager, Ton Eenennaam, is greatly interested in the study. “Although we are not considering putting a roof over the stadium yet, this is a very interesting development and it shows that solutions are available – even for existing stadiums,” he says.

Although a strong fan base assures nearly all home matches are sold out, the stadium would benefit from extra money generated by using the stadium for different purposes – particularly as it has decided not to sell its naming rights.

An artificial alternative
Enclosing a stadium is a particularly useful solution in countries where the climate affects the game. The Red Bull Arena in Salzburg, Austria deals with heavy snowfall during the winter. As a bidder to host the 2010 Winter Olympics, Salzburg planned to use the stadium as the main centrepiece of the event.

The stadium’s managing director, Wolfgang Becker, found an alternative to covering the Red Bull Arena with a roof. “We decided to have an artificial grass field installed which uses a heating system, to make sure we can still play games despite snowfall,” he says.

For stadiums in residential areas, a roof provides the added benefit of containing noise. But, says, Becker: “Since our stadium is located in an industrial area there is no need for that either.”

Of course, van Nunen and Verhoeven’s system will not be advantageous in all scenarios. But managers who decide that they prefer to have their stadium enclosed, once it is already up and running, will now have a solution.