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There will be little justice in this world if Oldham's library and lifelong learning centre doesn't win a hatful of awards. Not only does the £13³¾ terracotta tile-clad building blend seamlessly with its neighbour, the four-year-old Gallery Oldham - which has already received citations from the RIBA and the Civic Trust - it is also a model of energy efficiency at its best.

The library maximises its use of natural daylight and ventilation, as well as harnessing the thermal mass of the building's concrete frame, to minimise the energy it consumes for heating and lighting. It also has a sedum roof that harvests rainwater for flushing the toilets.

The library’s copper-clad performance centre protrudes from the main building

Ray Bibby, design and of Kier North West, says designing an environment-friendly building was a prerequisite to getting the contract. "Obtaining a BREEAM rating was part of our brief from Oldham council," he says. Kier led the Information Resources consortium that won the contract to build the library as part of a 25-year PFI deal worth £80m. The other members of the consortium were architect Pringle Richards Sharratt and multidisciplinary Arup, both of which had previously worked on the design for the gallery building.

Like the gallery, the library uses a large amount of fair-faced concrete, and the circular columns and soffits of the floor slabs are made of exposed concrete without painted surfaces. "Using the thermal mass of the exposed concrete was an essential part of the environmental statement that we presented to Oldham," says project architect Ian Sharratt.

The thermal properties of the concrete help lessen the energy required to heat or cool the building. Natural ventilation, an air displacement system that feeds conditioned air through floor vents, solar shading, and the concrete frame's thermal mass combine to create stable interior temperatures. The concrete frame itself was constructed by Burnley-based Reinforced Concrete Group, which completed the task in 32 weeks.

Exposed concrete is used to good effect throughout the library

The sedum roof is another element of the project that is integral to its energy-saving credentials. On top of the library's flat roof is a drainage membrane with a layer of geotextile fleece with lichen sown onto it. Rainwater percolates through the covering and runs into storage tanks in the basement plant room area where it is filtered and subjected to ultra-violet light to kill any bugs, such as E.coli, before supplying the building's 30 toilets. The system should reduce mains water consumption by at least 50-75%.

The project also ticks the right boxes for the way in which it dealt with the difficult brownfield site on which it was built. The site was previously home to a gasworks and so required a large amount of geotechnical work to counter the risk of contamination, which was done in the least damaging way possible. "We capped an old gas tank with a gas-proof membrane instead of demolishing it and carting the debris to a licensed site," says Bibby. "And there were old mine workings that had to be filled with grout. We drove friction piles into the clay layer rather than drilling into the rock so that any contaminants in the soil wouldn't get into the underlying aquifer."

Ideally, Oldham would have built the gallery and library as a single development, however the funding was not in place for both. As a result, the gallery was built with European Regional Development Fund money; then a couple of years later the library went down the PFI route. Sharratt says the library was always intended to project from the rear elevation of the gallery. But whereas the gallery's plan shape is straight and rectilinear, the 100 m long × 24 m wide library is kinked near its eastern end to maximise its location and provide stunning views across Oldham and the Pennines. Full height glazing on the eastern elevation and comfy sofas provide a marvellous chill out zone. "It's a good place to contemplate the view, particularly the dramatic skyline in the winter months," says Sharratt.

A two-storey glazed entrance foyer links the gallery on the left and the library on the right

The library is built on land sloping away from the gallery and its roofline has been kept lower so that the views from the gallery are not obscured. The two buildings are linked by a double-storey entrance foyer. Sharratt says some negotiating was necessary to enlarge the existing entrance foyer from 18 × 10 m to one of 18 × 18 m that would serve both buildings. This stemmed from the fact that the gallery and the library were built using different procurement routes, which raised problems over insurance liability.

In the end, an agreement was reached and the foyer, which is bathed in daylight, forms an impressive portal to the two buildings. Daylight also floods into the spine of the library from a north light that runs almost the entire length of the building. This is positioned above the staircases so that daylight reaches to the ground floor of the two-storey structure.

The overall effect of the environmental measures adopted is reflected in the fact that the library was awarded a "very good" BREEAM rating, exceeding the council's expectations. "We are very pleased with the outcome and the client is like a dog with two tails," says Sharratt. "Oldham is a town with a lot of pride, but for too long it has been considered a poor relative of Manchester. Now it has a building that reflects that pride."

The project could also be in line for a citation for the speed at which the PFI deal was put together. Declarations of interest were sought in July 2003 and Information Resources received preferred bidder status in December that same year. The project achieved financial closure in May 2004 and construction started one month later. As Bibby says: "It was a good project to work on, it's a great looking building, it finished on time and the client really likes it. And it made a little bit of profit for my company. What more could you want?"