What inspired The Shard’s design?
It was very important to us at Renzo Piano Building Workshop that such a tall building was accessible to the public. Around the world, the tall buildings that are known and loved – that are featured on T-shirts – are the ones that people can access, such as the Eiffel Tower and Empire State Building.

So, we didn’t want a normal city building that closed at 5pm on a Friday and opened again on Monday. It had to be functioning seven days a week, which led to the mix of uses – offices, restaurant, hotel, some apartments and a viewing gallery. The gallery is aiming for one million visitors a year and there are only 10 residents in the apartments, so they have very different uses, but are in the same building.

We wanted to create an open building so avoided using heavily tinted glass, which blocks out all life going on inside. Glass is an open, transparent material. You can see lights on inside, which show it’s functioning. By inclining the sides, it reflects the sky and the weather, so the building changes throughout the day, similar to a weather vane. The spire doesn’t meet at the top, so visitors feel the London air.

How does The Shard enhancethe capital city’s skyline?
London isn’t New York, Singapore or Hong Kong, where a tall building is just another skyscraper in the forest. In London there is no forest; the building is against the sky. The Shard’s spire shape is a form that has resonance throughout the UK as it echoes the outline of its historical churches. It also represents the masts of boats that used to moor in the Thames – tall, slender elements that rested against the skyline in old London.

Up until the 19th century, London Bridge was the only bridge across the Thames and was the centre of London. To have the tallest building next to the bridge, in the middle of London, is appropriate and gives definition to where the centre of London is.

What is the design’s message?
The building might be privately financed, but it’s not just a commercial venture that’s landed on the skyline – it’s a building that the public can enter: to visit the restaurant; stay at the hotel or go to the top to see the view.

People often think that architecture is just about aesthetics and the physical elements, but this is the political, social side of architecture.

What was the brief?
We had a very, very brief brief. In fact, the page was blank.

The most important thing with a good building is a good client. The client listened to us and we listened to them. It’s a shared vision.

Initially they didn’t like the sound of a viewing gallery, but then realised it had commercial viability to it as well as a socio-political importance in gaining acceptance of the project.

What were the challenges?
The first challenge was planning. This building represents a change for the city. Not only is it substantially taller than the others, it’s mixed use, which no other tall building in London is. It took three-and-a-half years to get planning. We had to go through a public enquiry, which costs a lot of money.

The principle opponent was English Heritage. There are protected views of St Paul’s Cathedral and we’re in the backdrop of two of those views. We argued that as we’re replacing some pretty uninspiring views that are already in the backdrop, we’re improving the situation and fortunately the planning inspector agreed with us.

Getting tenants was another challenge. The client had to get some to prove the viability of the building. Fortunately, they got two tenants early on – Shangri-La took the hotel in 2005 and Transport for London took office space in 2006.

The biggest challenge was financing the building. The client had financing in place in 2008, then the credit crunch came and the funding was withdrawn. Fortunately, at that time, the Qatari government had also been interested and they stepped in as both investors and financiers. So they gave us the mortgage and bought the house as well.

Of the four hurdles – planning, getting tenants, financing and building it – building was the easiest bit as, weather permitting, we could just get on with it. We have a big, experienced, knowledgeable team who are used to constructing tall buildings. It’d probably be more of a challenge for us to do a kitchen extension, as we’re not used to it!

What’s the evacuation process?
Post 9/11 people are much more aware of evacuation strategies. We use the lifts to get people out – they have a back up power generation and smoke pressure relief and are quick and safe.

With a mixed-use building it’s a challenge because everyone has their own lift banks: there are 43 altogether.

How does the architecture enhance the experience?
You could argue that you could see the view from the top of a beanpole, but I think the building is important. Consider the Rockefeller Center and the Empire State Building. In many ways the Rockefeller’s view is better because you can see Central Park and the Empire State Building, but the latter gets many more visitors because it’s an iconic building. Similarly, in Paris, the Tour Montparnasse is a horrible building – it’s the only skyscraper in Paris and went up in the early 1970s – so, despite its great view, it gets a fraction of the visitors that the Eiffel Tower does.

I hope people come to visit The Shard because they’re interested in the building, as well as the view.

We’ll only know if it’s worked in five or six years’ time if people are wearing The Shard T-shirts and if it’s viewed as an image worthy of London – a 21st-century layer to a very old city.

William Matthews is project architect at Renzo Piano Building Workshop