Architecture: Sensuality out of old brutalism

The GSW tower in Berlin defies gravity, embraces its environment, celebrates colour - and it's designed by Brits.

As Berlin celebrates being the capital of a reunified Germany, another balancing act is taking place on what used to be the Berlin Wall. Defying gravity, and apparently without foundations, a high-rise office block emerges from a low building and cantilevers out at a dizzying angle over Kochstrasse. And as if that wasn't enough of a surprise for Berliners, who experienced vertigo as they watched it go up, the architects Sauerbruch Hutton had the audacity to colour the skyscraper in eight shades of red, from flesh to terracotta.

"When I saw it was red I nearly fell off my bike," wrote one passer-by. No surprises that even before its opening in September, the building has already got a starring role as a key location in a new thriller movie.

Although based in Berlin, Louisa Hutton and her partner, in marriage as well as practice, Matthias Sauerbruch, are Londoners. They lifted off the entire roof of their own house in Notting Hill and replaced it with glass. But stringent German controls on street elevations have grounded some of the most influential international architects in Berlin, so this building is a triumph for the duo.

When Sauerbruch Hutton won the competition in 1991 to rebuild a pounds 58m HQ for a social housing organisation called GSW, they inherited one lonely, 16-storey tower built in 1961 when Kochstrasse was the Fleet Street of Berlin. The Wall, built a few months later in the same year, dramatically demoted that tower from being fashionably downtown, marooning it on what was then the outskirts of the West. It was further dwarfed by the Axel Springer publishing group building, clad in gold to flaunt its capitalism. The East retaliated with four Soviet-bloc high-rises.

This bleak wasteland, dotted with King Kong architecture, immediately interested the young practice, who like having master plans. Gripped more by the notion of fitting contextual buildings into a much broader landscape than making one-off architectural statements, this time - with sleight of hand and the help of engineers - they have managed both. Their GSW building vividly symbolises the rootlessness of the site and also picks up on its layers of history.

Sauerbruch Hutton also intensify the disquieting business of building a tower on a springboard by resting the cantilever upon a second long, low building, which runs 114 metres down Kochstrasse. On top of this mall, which will house shops at the furthest end from the tower and generate income for GSW, they set a fourth building, this time small and circular, which is why the architects call it "the pill box". The implication is that without it weighing down that corner, the springboard would tip up under the weight of the tower. (Of course, it won't.)

Some of the columns are hung from the beams of the main structure to enable a clear 14.5m span where you enter the building on the ground floor. Wind-tunnel testing in Bristol proves that the GSW cluster could withstand a "twister". This is a dynamic game that they are playing.

The tower on its west side, which gets the sun, is coloured in a mosaic of reds by louvered mesh screens, grouped at the window bays in threes. These can be pivoted, or pulled back flat out of sight behind the glass facade, which effectively takes out a block of colour at a time. Pushing a button to get the right light levels needed in the offices at any time of the day changes the colour combinations on the facade. "This makes the building dynamic rather than static," Louisa says. "Also, I like the way the facade randomly and seamlessly reflects what's happening in the building."

The Sauerbruch Hutton installation plan for these panels is as artistic and rigorously controlled as a Sol Lewitt painting. So their concern that the inhabitants control their own environment - and change the way the building looks at the same time - is interesting. Perhaps that's why the offices within are all such green, pleasant, and light-filled spaces. Natural wind draughts ventilate the offices and instead of long, impersonal corridors like something out of The Shining, there are swooshing, sinuous ones. Some of the offices along these corridors are configured as open plan, others as cells off central corridors, what the Germans call zwei- huftige (or double-hipped). It is a flexible arrangement that flows organically around peanut-shaped columns. "Grid systems make me see red," says Louisa. "It's just another word for lazy thinking." Of course, there is a grid to this building, it's just that the architects use it as a means to an end, not an end in itself.

Girdled with belts in verdant green that range from lime to sage, the little pill box nearly didn't get planning permission on account of its colour palette. Why couldn't it be more like the virulent green so loved in Germany for kitchens, and that Aldo Rossi used on his office block on the other side of the street? After listening to the architects' impassioned pleas, the planning officer agreed that it was their informed choice and let it go.

"Can you imagine that happening in Britain, where we're having such trouble getting plans for a house through Norfolk county council?" Louisa says, incredulous. And all the more so for having manipulated Berlin's rigorous street planning laws which insist on a certain touchdown for street elevations at 22 metres. By arching the new low-rise back from the street rather than bringing it out to the allowed frontage, the tip of the attenuated cantilever can stretch to the limits.

The two low buildings that slice across the site, covered in charcoal ceramic, are called "Baguette" and "Baguettini" by the architects. As one walks through the Baguette into the ensemble of five buildings on site, there is a load-bearing, toughened-glass panel on the first floor overhead that permits the visitor to see into the high-rise from the street. Here, bright blue signposts designate public spaces and commercial areas.

"Sensuous" is a word Louisa Hutton uses a lot to describe this interchange of ceramics with concrete and glass: this play upon rough with smooth, mirrored with polished, clear with opaque. And colour. Both partners believe "it's the missing dimension in modern architecture".

Yet when Louisa Hutton met Matthias Sauerbruch in the Seventies at the Architectural Association in London, colour wasn't even on the curriculum. Texture was everything, from steel to glass to concrete. Her first - and only - job upon graduating was working with Alison and Peter Smithson at Bath University. The Smithsons introduced that peculiarly British school of Corbusian modernism in the Fifties, which was known as Brutalism on account of its exposed concrete - rough to the touch, carved out, and endlessly colliding in big chunky shapes - which Louisa insists that she loves. No other aesthetic movement would get away with being called Brutalist (can you imagine Brutalist sculptors? Or water colourists?).

Yet Louisa Hutton's favourite Smithsonian flourish, and the one from which she has taken the most, is The Economist building in St James's, which she describes as revolutionising the way that buildings could create space in the city. Here, an intimate piazza some six feet above the pavement level leads into the main building. Similarly, to unify the cluster of five buildings at GSW, Sauerbruch Hutton seamlessly joined inside with out by letting the pavement, which is granite, flow indoors to the main entrance.

In another Sauerbruch Hutton design just outside Berlin, the Photonics laboratories where fibre optic cables are made and light experiments take place, the tarmac covering the trapezoidal industrial park flows into two amoeba-shaped, clustered buildings, like single-cell life evolving in a pool. The undulating shapes appear to change as the colour from blinds and columns behind its glass facade change from blues and greens on the north side to warmer reds and yellows on the south side. In every light, and depending upon your viewing point, these buildings change shape. Once again, the colour is not slapped on to camouflage the building, but is intrinsic to the function of the building, from the blinds and shutters that control daylight down to the labs and the colourful columns in pairs behind the double glass facade that control the flow of fresh air and the expulsion of exhausted air. The Photonics building lives and breathes fresh air. Amid the silver birches and beeches the architects celebrate this truly "green" building with crayon-box exuberance.