Athen's amazing roof

Behind the scenes on the design and engineering involved to create the world’s largest glazed roof for Athens Olympic Stadium

By Gary Henton, Palram Europe, manufacturer or extruded thermoplastic sheets

The last Olympic Games, held in Athens in 2004, combined the old and the new in more ways than one. Of course, there were the sports; everything from the sprint (the only event at the first games in 776 BC) to women’s freestyle wrestling (introduced as an Olympic sport in 2004). Then the location itself, with Athens being the site of the ancient Games as well as the first modern games held in 1896. Less obvious was the main stadium itself, a stunning combination of old and new.

The main Olympic Stadium; Olympiako Stadio Athinas Spyros Louis was originally completed in 1982. Located at Maroussi, the stadium is the main venue in the vast Athens Olympic Sports Complex (OAKA). Following Athens’ successful bid for the 2004 Games, work began in earnest on turning the 20-year-old city stadium into a modern venue that could meet the exacting standards required for such a high-profile international event with a worldwide audience of 3.9bn.

Renowned Spanish architect, Santiago Calatrava, who had previously designed the striking Montjuic telecommunications tower for the Barcelona Games was to inspire the renovation of the stadium and turn it into the centrepiece of the 2004 Athens Olympic Games. The key to the transformation of the building into an ultra-modern facility was the design of the roof which covers approximately 95 per cent of the 72,000 seats. The area of the roof, at 24,000 sq m, extends in two giant waves over both sides of the stadium.

The aqua-hue roof panels which then sit in the waves were originally specified to be glass. However, after a detailed process that included close consideration of all the various engineering and structural aspects of the project, it was decided to cover the stadium with polycarbonate panels. Polycarbonate offered the advantage of lower weight – its density is less than half that of glass – and superior durability as it is practically unbreakable.

The weight-bearing construction of the roof was made of two pairs of steel arches connected with torsion cables. The structure was additionally trussed with a system of diagonal connectors. Girders connected to the lower arch created the grid on which the polycarbonate panels were then fitted. Aside from the weight and safety considerations, the design team also had to accommodate an important public health issue: exposure to the sun and, in particular, the harmful portions of solar radiation.

Thermoplastic sheet manufacturer Palram’s Project Support Centre received the specification for a polycarbonate panel with stringent mechanical, solar and aesthetic requirements. The timetable was very tight since the specifications were completed with less than a year to go before the start of the Games. However, Palram’s engineers and technologists worked around the clock and succeeded where others failed, to produce a sample that would meet the unique specifications of this project.

In addition, due to the unusually low slope of the roof, it was necessary to find solutions to the consequential problems of sealing around the panels and drainage. This difficulty was overcome through a collaborative effort between Palram and roofing contractor, Gallop Skylights of Nicosia. The resulting GA-2004 glazing system was designed to provide a solution for the roof glazing installed where the slope was extremely low.

The patent-pending system was designed to ensure both sealing and drainage while maintaining a smooth, clean line without interruption from additional profiles. The absence of an upper profile also delivered an important benefit – true self-cleaning. Dust, rain water and snow could not be blocked at any point so water could flow freely, cleaning the panels automatically during each significant rainfall. The runoff is then gathered and removed by a built-in system of gutters and drainpipes, and together with three levels of sealing makes the GA-2004 system suitable for even a 0° slope.

It is essentially a floating system and therefore also deals with the problem of thermal expansion and contraction. Each panel is free to expand and contract without disruption to the integrity of the structure or seal – particularly relevant in a place like Athens that can experience quite dramatic temperature variations.

Strict quality control was deployed from extrusion through to installation, with supervision on-site greatly improved by fitting the panels into a cassette on the ground. They were then raised to the roof line and dropped in to the desired location. This also had the added advantage of speeding up the installation process and reducing the associated costs.

Branded Palsun Solar Olympic UV2, each of the 12mm-thick polycarbonate roof panels measured 4042 x 952mm and weighed in at approximately 55kg. To complete the roof structure, a total of 4,750 individual panels were produced at Palram’s extrusion facility in Doncaster, UK. The Solar Olympic sheet included an integrated and co-extruded UV protective layer and an abrasion resistant coating on both sides to withstand the intense Athens summer sun and the city’s infamous pollution.

The panels also blocked out 99.99 per cent of incident UV solar radiation, a fact recognised by the American Skin Cancer Foundation when they awarded Palram with their Seal of Recommendation. Thus, the spectators in the stadium were well protected, even during the hottest part of the day.

The Athens stadium renovation and roof structure reached completion just ahead of the opening ceremony in August 2004 and now, over two years hence, visitors can clearly see the quality of the panels remains undiminished. There can be no doubt that the design and engineering involved to create the world’s largest glazed roof has helped to create a venue to stage major events for years to come. Indeed, the final of European football’s premier competition, the Champions League, is scheduled to be held in the stadium this year.