Norman Foster: Portrait of a master builder

You have to look closely to spot him. At first, there's only a vague whiteness, marbled with grey-blue shadow. And then you notice it: a small shape, moving diagonally across the snowscape, a Lear sheathed in Gore-Tex. It's Norman Foster, who has been the world's single most powerful and influential architect for three decades. But what is Baron Foster of Thames Bank doing in an out-take from Fargo?

The glacial opening scene belongs to a tantalising new film. With a 74-minute running time and a big budget, architecture has been given a filmic gloss not seen since 1949, when Gary Cooper starred in The Fountainhead, a stilted study of modernist design angst stained with the shadows of High Noon. Sydney Pollack's Sketches of Frank Gehry, filmed in 2005, is Foster's only contemporary competition in the posh architectural portrait stakes.

The new film, How Much Does Your Building Weigh, Mr Foster?, is an elegy, produced by Foster's wife, Lady Elena Ochoa, that won't quite admit to being an elegy. It is beautifully shot, the soundtrack is elegant in the extreme, the script carefully cadenced. We see the great man as he wishes to be portrayed, and we now know – Foster was originally asked the question by the visionary engineer Buckminster Fuller – that the Sainsbury Centre for Visual Arts in Norwich weighs precisely 5,328 tons.

The lens is enquiring, the Steadicam "float" over the Millau Bridge in France is breathtaking, and the speeded-up vision of Hong Kong injects a rather forced element of on-trend hallucination. But we still don't know how much Norman Foster's soul weighs.

The desire to know the heft of that metaphysical substance is impertinent, but unavoidable. How can a man of Foster's architectural achievement not interest us greatly? This is a 76-year-old who has been on the verge of bankruptcy, but is now personally worth more than £200m; a man who was given three months to live a decade ago, following two jousts with cancer, yet still participates in the Engadin langlauf ski marathons in Switzerland. So, what makes Norman run?

In a craven new world awash with the tranquilising soma of info-tainment, that question must be posed carefully or it will produce trivial answers. The film, scripted by Deyan Sudjic, director of London's Design Museum, is a civil and gracious collage of reportage, interviews, and musing speculation. There are moments when we get what seems to be the unvarnished, fully exposed Foster. However, just as with his authorised biography of Foster, Sudjic does not broach the central riddle: what is it that makes the prose of our lives flare into brilliant passion, yet turns other passions into ashen prose?

The key questions about Foster don't concern his obsession with the techniques of seamless modernist architectural perfection. In this, he is masterful. The almost completed Masdar zero-carbon city in Abu Dhabi also makes Foster + Partners the world's leading techno-environmental designers. And they are the go-to architects for Pavlovian corporate leviathans desperate for a Foster exclusive.

He tells us he pursues his craft for the benefit of mankind and says: "Sometimes, I think I see things that other people don't." It's possible, of course, that other people occasionally see things that he doesn't. Or see things in his work that don't exist. The film's voiceover murmurs that the metal diagrid corners of the Hearst Tower in New York "dissolve into thin air" when they very patently do not; and the claim that the genuinely astonishing Millau viaduct reminds us that "we'd forgotten how useful things could be this beautiful" is jarringly unctuous. Of course we haven't forgotten.

Nevertheless, Sudjic's portrait makes some deft incisions into the flesh of Foster's being, and he begins and ends the film with highly significant statements that almost suggest criticism. Over a panning shot of the Willis Faber building in Ipswich, he says: "There's something about his architecture that's hard to read. How do you understand a building of black glass, a curved screen? You don't know quite what's going on inside. And maybe that's Norman also." At the end of the film, Sudjic wonders if "a world covered end to end in Fosterism is not a good idea." And?

The film presents some extraordinary moments. The hiss and chaotic visual blurs of langlauf skiers; the sun setting through the glazed facade of Beijing airport's vast third terminal. And here's Foster himself, gingerly approaching the front door of a dour little semi on the wrong side of the tracks in Manchester – the house he grew up in, and was revisiting for the first time in 30 years. We witness his intense, boyish concentration as he gets a steam-powered boat going for his young son; and we see him, three decades earlier in black-and-white footage, enthusing about a lightweight wall panel as if he were a messianic travelling salesman, an architectural Reginald Perrin.

Most gripping of all, we see Foster draw, for it is when he draws that he talks most comfortably; he's in the zone. He re-draws his first sketch, originally made in the early 1940s in his cramped upstairs bedroom. It shows a charmingly bloated aircraft with a tiny figure in the cockpit, several storeys above the ground. It's powered by several kilometres of entwined rubber-bands. "There's a sense of control and command," he explains. And a sense, too, of the ultra-secretive Hollywood director-cum-industrial magnate Howard Hughes, and his giant Spruce Goose seaplane.

Sudjic, the good shepherd, nudges Foster into talk of "the spiritual dimension which is rooted in all the senses, and which you can't measure." And he speaks of transformations: "We've reinvented the airport. We've reinvented the nature of the high-rise. All of us, in one way or another, reinvent ourselves in terms of changing circumstances, or from experience or knowledge, or feeding off new challenges."

Far more intriguing, though, are Foster's remarks about the "poetic" nature of gliding, and the loneliness of the long-distance skier: "It's a very isolated thing to do. You're alone in physical determination. You have to finish... I think I need the silence. It's not an escape. It's a complementary activity." And even when he talks about Richard Long, an artist he greatly admires, it is Long's "endless personal pursuit" that he highlights.

Another close friend, Lord Weidenfeld, says of Foster: "He wants to prove that he can conquer weakness. He wants to conquer infirmity in the sense that he wants to show how far one can do through willpower." Foster says he'd love to redesign every single project: "You can always go one step further. And if you can't go one step further it means that you haven't learned from what you've done before – and you're not sharp."

For Foster, the film star, the wheel of karma has two tracks: the pursuit of a technically perfected world, and the eerie Om of an obdurate human pulse beating in the void. Perhaps, as in T S Eliot's poem "Little Gidding", Norman Foster will not cease from exploration, and at the end of all his exploration will arrive where he started, and may then know the spiritual weight of that place for the first time.

'How Much Does Your Building Weigh, Mr Foster?' is out now

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