Art Institute of Chicago by Renzo Piano Building Workshop, Chicago, USA

Few contemporary architects have such a strong commitment to purpose and place as Renzo Piano. Each of the eight US museums he has built or extended, from The Menil Collection in Houston (AR March 1987) to the California Academy of Sciences in San Francisco (AR November 2008) is shaped by context and programme. The newly completed Modern Wing of the Art Institute of Chicago is no exception. It comprises two blocks of galleries extending north from earlier additions to the Beaux Arts original, linked by a skylit concourse and shaded by aluminium blades set into a lofty white steel canopy. Limestone from the same quarry as the 1893 block clads the side walls, and a double glass curtain wall to the north dissolves the mass.

‘It was a privilege to build in Chicago,’ says Piano. ‘It’s a place of myth for me. As a young architect I saw it as the city that reinvented itself after the great fire, using steel balloon frames to create buildings that were light and vibrant. It invented modernity, and my buildings try to connect with that legacy.

‘Relics of Louis Sullivan’s Chicago Stock Exchange, preserved beside and within the art institute, are tangible reminders of the city’s modern origins. Survivors from the first generation of master-builders are cherished landmarks, as are the urbane towers of Mies van der Rohe. But those are scattered highlights. Most recent construction is as banal as in any American city, so Piano’s addition is a welcome return to the principles that sustained the myth. It conducts a dialogue with history and with arts and landscape centre Millennium Park to the north.

When Frank Gehry completed the Jay Pritzker Pavilion - a baroque swirl of steel plates enclosing a concert shell - he issued a friendly challenge. ‘Come and get me,’ he told Piano, who was finalising his design. The Italian did just that, exploiting the rigorous street grid to align his concourse on the pavilion, counterpointing Gehry’s exuberance with his cool rationality. ‘He works in his language, I with mine, but the two projects do a similar job,’ says Piano. ‘He created an acoustical space and we created a visual space protected from the sun.’ To tie the two together, a slender 180m-long footbridge slopes gently down from a rooftop sculpture garden to the middle of the park, complementing the equally graceful span that Gehry designed to link landscape with lake shore.

All this might have turned out differently but for a serendipitous encounter. As Piano recalls, ‘I was in Chicago in 1999 and James Wood, the Art Institute director, invited me to stop by. A number of people came and we had a very informal conversation about their plan to expand. Later I understood that was the selection process. I like it when there is an exchange of ideas. Competitions are too often like beauty contests.

‘Initially, the goal was to add galleries on the south side, as the largest of seven successive additions to the original building. By late 2001, it was clear that Millennium Park was becoming a new centre of activity. The Goodman Theatre facing the park across E Monroe Street had relocated and the institute was able to acquire and demolish its old building. That provided a larger, more prominent site, with the opportunity to create a bold cross axis that would bring a sense of order and connectivity to a muddled east-west sequence. As Piano observes: ‘The old galleries offered an incredible place to view art but people got lost easily.’ The desire to bridge a busy street led to the idea of a sloping promenade, accessible to the disabled, which would draw people in from the park. As graceful in its profile as the hull of a skiff, the footbridge doubles as a belvedere offering a panorama of the city and as another point of entry.

The transparency of the north facade turns the axial concourse named Griffin Court into a public gathering place, alive with school parties using the educational centre to the east and visitors to the shop and temporary galleries on the west side. The shallow pitched skylight is cable-braced like the rigging of a ship.

Piano believes that museums need to balance sacred and profane space, and the bustle of the ground floor gives way to the serenity of the galleries for modern and contemporary art on the two upper levels. ‘You “take your shoes off” and you go up - it’s a different world,’ says the architect.

There’s a seamless link between the white oak floors and benches. On the top floor, you can glimpse the sky through the canopy that projects beyond the building and the thin fabric that filters the light. The blades are computer controlled to respond to fluctuations in the intensity of light and photovoltaic cells in window scrims conserve energy. An exemplary collection of modern classics from the first half of the 20th century is suffused in natural light. On the level below, contemporary art and the rich collection of design and architecture are displayed in galleries that flow into each other and draw natural light from windows and the concourse. An encyclopedic museum that has collected contemporary art since it was founded 130 years ago, now the full sweep of the institute’s holdings is finally on view.

The grandeur and intimacy of the galleries matches the engaging presence of the exterior. ‘For me, a building never stands alone. It’s a piece of the city,’ says Piano. He has woven the Modern Wing into the fabric of a heroically scaled metropolis as successfully as he accommodated The Menil Collection to the scale and character of its residential neighbours. The new structure is rigorous but welcoming - a measure of quality and relevance for Chicago, where the guiding vision was eclipsed for several decades. It also provides a subtle riposte to the overheated, ego-driven world of museum design.