Midwest modesty: As part of an ambitious landscape regeneration strategy, Chipperfield brings figure to the city grid.

The public library in the United States has long been considered an important underpinning of its democratic and capitalist society. Initially, imposing public libraries, signs of civic prosperity and pride, were important instruments of city building. But in a nation that has enthusiastically embraced suburban and exurban living, downtowns have declined and previously vibrant urban libraries have struggled to survive. However, what might have been a tale of extinction has--in a number of US cities including Phoenix, San Francisco, Salt Lake and Seattle--been rewritten as a happier story in which the public library is playing a pivotal role in urban regeneration. The most recent addition to these ranks is Des Moines, where a new Central Public Library designed by David Chipperfield has just opened.

The former central library, a lavish 1903 Beaux Arts edifice, was built by the city's burghers as an innovative civic centre that also housed an art school and gallery. Over the years, the library outgrew the building, which became tired and obsolete. Des Moines, the state capital and one of the largest centres for insurance business in the US, has a healthy economy but, like many American cities, its downtown is an uneven patchwork of corporate offices, underused historic buildings and parking. The centrepiece of the city's regeneration strategy is a new park designed by Zimmer Gunsul Frasca and executed at the same time as the library. The library is strategically placed at the east end of the park to act as a connector between the central business district and the park. Together with other initiatives--including investment in downtown K-12 schools and city centre housing--the park and library are stimulating further development around the site, including a recently completed centre for university outreach and continuing education, expanded corporate offices and a new entrance to the university's medical centre.

In a city defined by the Jeffersonian grid, the library pulls away from the orthogonal edges of the site to take on a figural character appropriate to its status as a civic institution. Fluid interaction between building, park and city enables the new library to adapt seemingly effortlessly to the presence of a former Masonic temple on the south-east corner of the site, which now houses a theatre, restaurants and that ubiquitous marker of urban vitality, Starbucks. The form of the building creates outside spaces of different characters and helps to pull pedestrian circulation through the site. To the north, the library's formal entrance is marked by flagpoles and flanked by a library shop/gallery. Around the Masonic Temple, the interstitial zone is filled with outdoor restaurant seating and a chess garden for the library, while to the west, the park predominates. From the south, east and west sides of the site, pedestrian routes converge in a generous covered double-height public passage through the building that incorporates a second entrance to the library together with access to a new cafe and a range of flexible public meeting rooms that can operate either independently or as part of the library.

The rigorous coordination of services and structure with plan and programme produces a tightly integrated, yet highly flexible space that is amenable to individuals, groups of varying sizes and the evolving character of the library's collection. Structure and services are compressed to yield maximum height for the internal spaces. The two-storey site-cast concrete structure combines 600mm diameter columns on a 9m grid in the heart of the plan with a necklace of 400mm diameter columns at 6m centres to pick up the irregular perimeter. To carry the heavy loads of the stacks, flat concrete slabs are, unusually, 450mm thick. Laid out to preserve views through the building to the park, stacks run either east-west or north-south, parallel with the urban grid and the formwork joints for the slabs. Instead of a central reading room, a variety of study and lounge spaces is dispersed around the perimeter.

Services are supplied through a 400mm deep raised floor--exposed by glass panels in the children's library as a teaching tool--which also forms a low pressure plenum. Perimeter heating and cooling loads are handled by fan coil units that supply air to a continuous stainless-steel floor grille. Ceiling services, including lighting and sprinklers, are carefully coordinated beneath an exposed concrete soffit, which provides thermal mass to reduce the cooling load and minimise temperature swings. Rising sprinkler mains in rebates in the concrete columns feed a network of horizontal pipes close to the soffit, while simple linear fluorescent batons are suspended 900mm below. This pared down simplicity is echoed in monolithic black terrazzo stairs with painted steel sheet balustrades and soffits; in apparently solid and seamless white Corian circulation desks; and in the lounge chairs designed by Chipperfield for the building. The subdued interior material palette is the foil for three walls of vibrant colour--pale blue for the cafe and meeting rooms of the south wing; kiwi green for the administrative offices and back-of-house support in the east wing; and yellow ochre for the children's education room, special collection and staff offices in the west wing.

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Chipperfield's restraint is reiterated in the energy efficient building envelope, a taut insulating skin of frameless triple-glazed units, which contain a leaf of expanded copper mesh held between the outer sheets of clear glass. The structural silicone jointed panels are 1.2m wide by 4m high. The mesh performs like microlouvres, significantly reducing glare and the cooling load on the building. By virtue of a recessed reveal at grade, the entire facade appears to hover on a 400mm 'plinth' of precast concrete cladding panels. The repeating module gives the building both a uniform visage and, in the way it works, variable faces and characters. Externally by day, the cladding creates a strong boundary between inside and out, allowing no glimpse of the life within the building; inside, the mesh dematerialises to reveal a fully glazed building offering generous views out in all directions. At night, the effect is reversed. Nocturnal library patrons are cocooned within a dense copper wrapper illuminated by perimeter downlighters, which transforms into a visually permeable veil when viewed from street and park. The skin also provides a touch of opulence in the boardroom, where the meeting table is a single glass and copper mesh cladding panel. Finally, the 5000sqm flat roof is planted with sedum, which also contributes to energy efficiency and further develops the relationship of library and landscape for those overlooking the site from surrounding buildings.

Libraries are no longer treasure houses of books but instead have become both clearing houses for knowledge, information and entertainment and, importantly, centres of social exchange. With Chipperfield's new building, the city has both revisited and renewed the original library's concept of mixed use. Culture and consumption are now inextricably intertwined. The new library significantly expands and diversifies the collection, triples the number of computers available for public use and provides a wireless environment in which visitors can use their own laptops. In addition to the shop/gallery, cafe and meeting rooms, it has a digital teaching lab for public and staff training as well as dedicated computer clusters for children, teens and adults. Shopping baskets, carts and self-service checkout are provided like the supermarket, while books are displayed throughout the stacks and can be read in comfortable armchairs with a cup of coffee. Material can be checked out online and collected or returned at drive-up windows.

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The new Des Moines central library was commissioned in 2001 through an open request for proposals. David Chipperfield learned about the project in the course of his work on the Figge Museum in nearby Davenport and, once appointed, engaged in extensive public consultation. Four alternative schemes were offered for a public ballot, and their favourite has been built. The project has succeeded through the careful cultivation of many constituencies by a committed client and design team and has been realised by a partnership of the library, city and state, private foundations and individual donors. Public pride in the building is palpable, with every donation, large and small, acknowledged on the walls of the pedestrian passage through the site and the library busy with users of all ages and persuasions.

While minimalism is often dismissed as an acquired taste of the architectural cognoscenti, the appointment of David Chipperfield and the broad public support for this spare and uncompromisingly modern building suggest otherwise and confound the notion of a conservative American Midwest. Local citizens suggest that conservatism in lowa is less about tradition and more about being frugal and practical. The new library scores high on both counts. Submitting to a strict discipline and stripping away unnecessary finishes and flourishes, Chipperfield has achieved many efficiencies. Focusing on the supple form of the building and its shimmering skin, he has leveraged a modest programme and tight budget to create a powerful public presence.