San Mamés has always been called La Catedral. The old ground earned that nickname through noise, history and the slightly uncomfortable feeling that opposing teams were walking into a place where very unpleasant things tended to happen to them.
When Athletic Club moved into the new San Mamés in 2013, there was an obvious fear. Modern stadiums often gain comfort and lose character. They become cleaner, shinier and somehow less alive. Bilbao got something different. The new stadium kept the pressure and intensity of the old one, but wrapped it in one of the most striking roof designs in European football.
The roof at San Mamés is not simply there to keep supporters dry. In Bilbao, where rain arrives with the reliability of a defender making a last-ditch tackle, that matters quite a lot. The roof became one of the defining features of the entire stadium. It shaped the atmosphere, altered the acoustics and turned the stadium into a glowing landmark beside the Nervión.
Why the Roof Was So Important
The original design brief for San Mamés was difficult. Athletic Club wanted a modern stadium with better facilities and more seats, but they also wanted to preserve the intimidating atmosphere of the old ground.
The architects at IDOM understood that the roof would play a huge role in that. A football crowd becomes louder when sound is trapped and reflected back toward the pitch. A large open bowl might look impressive in an architect’s sketchbook, but it can also leak noise into the sky and leave a match sounding like an underwhelming pre-season friendly.
San Mamés uses a continuous roof that curves around the entire stadium bowl. The shape sits low above the stands and helps trap sound inside the ground. The result is one of the loudest stadiums in Spain. Visiting teams do not merely hear the crowd. They feel it.
There is also the weather. Bilbao is hardly famous for endless sunshine and dry afternoons. The roof was designed to protect supporters from the city’s frequent rain while still allowing natural light and air to reach the pitch.
The Structure of the Roof
The roof is built around a ring of large radial steel trusses. These powerful metal supports stretch inward from the outer edge of the stadium towards the centre of the pitch.
Instead of using a heavy traditional roof, the designers covered these trusses with ETFE cushions. ETFE, short for ethylene tetrafluoroethylene, is a lightweight transparent material often used in modern stadium architecture.
Compared with glass, ETFE is far lighter and easier to shape. It can let large amounts of natural light pass through while reducing the overall weight of the roof. That matters in a stadium where huge spans are required without blocking the view of the pitch.
At San Mamés, the ETFE roof panels give the structure a pale, almost floating appearance. During the day, the roof looks clean and understated. At night, once the lighting system comes alive, it becomes something far more dramatic.
Key structural details include:
- A ring of steel radial trusses extending toward the pitch
- ETFE cushion panels covering the roof surface
- A roof line designed to follow the curve of the stands
- Large spans without internal columns, preserving sightlines
- Integrated drainage and weather protection systems
The engineering challenge was considerable because the roof had to cover more than 53,000 spectators while remaining light enough to avoid overwhelming the structure beneath it.
The ETFE Roof and Why It Works
ETFE has become popular in stadium architecture because it offers a rare combination of strength, lightness and transparency.
At San Mamés, it solved several problems at once.
First, it reduced the weight of the roof. A conventional glass roof would have required a much heavier supporting structure. That would have increased both the cost and the visual bulk of the stadium.
Second, it allowed sunlight to reach the pitch. Grass at San Mamés already faces a difficult task. It spends much of the year dealing with rain, shade and the occasional footballer sliding through it with the subtlety of a runaway lorry. The ETFE roof lets in enough light to help maintain the playing surface.
Third, the material helped create the stadium’s distinctive appearance. The white ETFE roof works together with the twisting ETFE panels on the exterior façade. Together, they give the stadium a sense of movement, almost as though the entire building is caught in the middle of a gust of wind rolling in from the Bay of Biscay.
The roof also reflects artificial light extremely well. This makes the lighting system more effective and gives the stadium its famous glow on match nights.
The 2016 Roof Extension
When the new San Mamés first opened, there was one problem. Too many supporters were still getting wet.
The original roof looked elegant, but it did not extend far enough over the seats. In a city with Bilbao’s climate, this quickly became a serious complaint. Supporters in the upper rows remained protected, but many lower seats were exposed whenever the rain came in sideways, which in northern Spain is often.
Athletic Club responded by extending the roof in 2016.
The extension cost around €12.6 million and increased the roof’s effectiveness against rain by roughly 70 per cent. The new section pushed the edge of the roof further towards the pitch without damaging sightlines or making the stadium feel enclosed.
This was not a minor adjustment. Engineers had to add new sections to the existing steel structure and integrate them with the ETFE covering. The project was completed in time for the start of the 2016-17 season.
The difference was obvious immediately. Supporters finally got the protection they expected and the atmosphere improved because fans were no longer spending half the match checking whether they had accidentally brought a swimming costume instead of a scarf.
The roof extension later won an international structural engineering award, which is probably the closest an overhanging piece of steel and ETFE can get to receiving a standing ovation.
Acoustics and Matchday Atmosphere
The roof design does more than block rain. It is one of the main reasons why San Mamés feels so intense during a match.
The low, continuous roof traps sound and reflects it back toward the pitch. Combined with the steep stands, which sit close to the action, this creates a wall of noise that can make even routine league matches feel far more significant.
Athletic Club supporters have always had a reputation for creating a fierce atmosphere. The roof amplifies that tradition.
Data from modern stadium design suggests that lower roof profiles and enclosed bowls can significantly increase perceived crowd noise. San Mamés follows that principle almost perfectly. Sound from the crowd hits the underside of the roof and bounces back into the stadium instead of escaping.
That is one reason why San Mamés regularly appears in discussions about the best football atmospheres in Europe. On a European night, with the floodlights on and the roof reflecting every chant, the stadium can feel less like a sports venue and more like a giant pressure cooker.
Lighting Built Into the Roof and Façade
One of the most memorable parts of San Mamés is how it looks after dark.
The roof and façade work together as a giant lighting display. The stadium’s outer skin is covered with thousands of white ETFE fins and panels. These can be illuminated in different colours and patterns.
On match nights, the stadium often glows red and white, the colours of Athletic Club. During major events, the lighting can be changed to reflect other themes or competitions.
The roof itself helps create this effect because the ETFE surface reflects and spreads the light evenly. Rather than a harsh or patchy glow, San Mamés appears to float above the city.
From across the river, it is one of the most striking views in Bilbao. The old San Mamés had atmosphere and history. The new one has atmosphere, history and the ability to look like a giant lantern.
How San Mamés Compares With Other Stadium Roofs
Many modern stadiums use ETFE roofs or translucent panels, but San Mamés uses them in a more restrained and intelligent way than most.
The obvious comparison is with the Allianz Arena in Munich. Both stadiums use illuminated exterior panels and create a powerful visual effect at night. The difference is that Allianz Arena feels more futuristic and theatrical, while San Mamés remains tied to the industrial and maritime character of Bilbao.
Compared with Wembley or the Tottenham Hotspur Stadium, San Mamés has a lower and more intimate roof profile. Wembley uses its famous arch and a much larger open bowl. Tottenham has a sleek, sharp-edged roof with a more corporate look.
San Mamés feels different. It is not trying to impress through scale alone. It is designed to make the crowd feel close to the pitch and to make the stadium part of the city around it.
| Stadium | Roof Material | Key Feature | Atmosphere Impact |
|---|---|---|---|
| San Mamés | ETFE cushions and steel trusses | Low continuous roof with lighting integration | Excellent |
| Allianz Arena | ETFE façade panels | Colour-changing illuminated shell | Very good |
| Wembley Stadium | Steel and polycarbonate | Large arch and open bowl | Moderate |
| Tottenham Hotspur Stadium | Steel and glass | Sharp modern cantilever roof | Very good |
A Roof Designed for Bilbao
The best stadium roofs suit the place they are built in.
San Mamés sits beside the river in a city known for industry, rain and football. Its roof responds to all three.
The steel structure reflects Bilbao’s industrial past. The ETFE covering gives the stadium a modern identity. The extension solved the practical problem of keeping supporters dry. Most importantly, the shape of the roof helps preserve the intensity that made the old San Mamés famous.
There are more extravagant roofs in world football. There are larger ones and more expensive ones. Yet very few do so many jobs so well.
At San Mamés, the roof protects supporters, shapes the sound, defines the stadium’s appearance and keeps the spirit of the old Cathedral alive. That is a great deal to ask from a few thousand tonnes of steel and some translucent plastic.
Quite frankly, it earns its place.
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