One of the architects behind London's famous Gherkin skyscraper has now turned against glass buildings. Is it time tall towers were made out of something else, asks Hannah Sander.
It is one of the UK's most recognisable buildings. A Stirling Prize winner. A backdrop to Hollywood films. Named the most admired tower in the world.
But 10 years after it was opened, one of the designers behind the "Gherkin" has turned against it. Architect Ken Shuttleworth, one of the team at Foster and Partners who designed the tower, now thinks the gigantic glass structure was a mistake.
"The Gherkin is a fantastic building," he says. "But we can't have that anymore. We can't have those all-glass buildings. We need to be much more responsible."
The building at 30 St Mary Axe - nicknamed after a gherkin because of its bulbous silhouette - kick-started a decade of strangely shaped glass towers. The Cheesegrater, the Walkie-Talkie and the Shard loomed up from the pavements of London.
The skylines of both Birmingham and Manchester were drastically altered by the addition of towers by property firm Beetham.
One of the best-known glass building mishaps took place last summer, when the Walkie-Talkie at 20 Fenchurch Street in London was accused of melting cars. The 37-storey building reflected light in its glass facade and shone powerful rays at its surroundings. Cars parked underneath were damaged, and passers-by even managed to fry eggs using only sunlight.
In the end the developers, Land Securities, had to apply for planning permission to obscure architect Rafael Vinoly's £200m design with a permanent "brise soleil" or sunshade.
And yet despite this, Land Securities recently revealed that the widely reported calamity "did nothing to deter lettings".
Glass buildings are popular - not just because of their striking appearance but for the views they boast, and the increased light they let in.
When German architect Ludwig Mies Van Der Rohe designed what is said to be the world's first glass skyscraper in 1921, he associated the glass facade with purity and renewal. Later in the century, British architect Richard Rogers praised glass buildings because of their social worth. Glass walls enabled even employees working in the basement to benefit from reflected natural light and dissolved barriers between a cramped indoor office space and the greenery outside.
Companies like to give the impression of a democratic working environment - open-plan and with floor-to-ceiling windows, so that all employees, not just the boss, benefit from the view.
However, as concerns over global warming have become more widespread, so the glass structure has come under scrutiny.
Since leaving Foster and Partners in 2006, Shuttleworth has become a key voice in the fight against glass. Despite his background working on giant glazed buildings, he has founded an architectural practice in which floor-to-ceiling windows are considered an archaic luxury.
"Everything I've done for the last 40 years I'm rethinking now," he says. "If you were designing [the Gherkin] today... it wouldn't be the same product all the way around the building.
"We need to be much more responsible in terms of the way we shade our buildings and the way we thermally think about our buildings."
Glass lets out and lets in a lot of heat. A vast amount of energy is required for an office full of people to remain cool in the UAE and to stay warm in the snowstorms of Toronto.
Governments are now so concerned by the long-term impact of "solar gain" - the extent to which a building absorbs sunlight and heats up - that they have introduced strict regulations around shape and structure.
Architects are being encouraged to change where they place windows, so that a sunny south-facing wall has less chance to absorb heat than a chilly north-face.
Walkie-Talkie developers Land Securities are currently at work on a building called the Zig Zag, that is designed so that alternate walls cast shadows on their neighbours. The building is deliberately shaped so it can keep itself cool.
In the US there is a campaign in favour of wooden skyscrapers, promoting wood as a "green" building material in place of glass.
However, the trade association Glass for Europe has dismissed what they consider "a preconceived idea" that glass is bad. Instead they point to sustainable buildings in which glass has been fashioned into corridors that don't require central heating and solar panels that have been slotted seamlessly into a design. The association also points out that glass is fully recyclable. "A whole palette of glass products is available for the glazing to meet different functions in the building envelope," the association said. "Glass is fit for all climates."
In the past decades, the glass industry has worked hard to adapt technology in the context of climate change.
Engineer Andrea Charlson is part of a team at firm Arup that seeks new ways to increase material sustainability. She is not convinced that the glass in glass buildings is the cause of their problems.
"There have been a lot of advancements in glass technology in the last few years and it's amazing what we can do now in terms of putting coatings on glass. Some of them can be a heavy colour tint that will provide some shading. Others will be almost invisible but will still keep a lot of the heat and solar gain outside a building," she says.
Charlson is currently investigating problems in the materials that hold the glazed panels on buildings in place.
"As the glass technology improves, one of the biggest causes of heat loss is through the framing. The heat energy will always try to find the path of least resistance."
Even with the improvements to glass technology, Shuttleworth is not convinced that these sheer skyscrapers can be justified in today's society. He is not only concerned by their environmental impact, but also with the other effects a glass tower has on its surroundings.
Architecture and design critic Tom Dyckhoff is equally keen to see the glass skyscraper put to bed.
"As someone who spends their entire life staring at buildings, I am a bit bored by the glass box. They were radical in the 1920s and now they are just cliches, expensive ones at that.
"But now that we are having to be more thoughtful about how and where we use glass, maybe architects will become more inventive in how they use windows, instead of plastering them across whole facades," he says.
Shuttleworth's most recent project began life as a solid steel object and he says it has glass only where it is needed.
"It is a privilege to have a window. I think it should be seen as a privilege," he says.