How did they do that?

Will Alsop, senior partner of architect Alsop & Störmer, is keen to reassure British clients that his non-conformist designs do not entail greater risk than more conventional building forms. "None of our buildings has fallen down, they're all built on budget, and they've all got good maintenance records," he says.

Although the Peckham library's technology is not its aesthetic centrepiece, as it is with the buildings of Richard Rogers Partnership and Nicholas Grimshaw & Partners, the design is backed by considerable technical expertise. It is also a sustainable, low-energy building, gaining an "excellent" rating under the Building Research Establishment Environmental Assessment Method.

How the pods were built

The three large pods in the main library hall were constructed on frameworks of timber carcassing. "At first we thought of using concrete because of its thermal mass," explains project architect Andy Macfee. "But it would have been quite heavy and expensive. Metal construction was also expensive. We then thought we would try the craft of boat-building, but boat-builders imagined that the structure would have to survive force-eight winds." In the event, the contract for the gourds was awarded to Cowley Structural Timberwork of Lincoln, which has a track-record in church domes and worked on Branson Coates' Oyster House, the star of last year's Ideal Home Exhibition.

The irregular double-curving form of each gourd was prefabricated as three horizontal slices measured off 3D computer models.

The timber carcassing was craned into position and then stiffened with laminated veneer timber boarding to form a structural skin.

The "patchwork" cladding to the gourds takes the form of small squares of 1.5 mm thick aeroplane plywood that were overlapped and carefully stapled to the underlying boarding, with the copper staples exposed like patchwork stitching. The interior surfaces were sprayed with a white, sound absorbent finish.

Building structure

Designed by structural engineer Adams Kara Taylor, three main elements make up the overall structure of the inverted L-shaped building.

The five-storey vertical block is supported on an insitu concrete frame that includes diagonal bracing and deep floor troughs. The frame is exposed, and its surface has been sand-blasted and finished in a light-grey Keim paint to give a soft, smooth appearance like foam rubber. The overhead library hall is supported on deep steel trusses at 3 m centres. The seven spindly stilts that prop up the outer side of the library hall are 323 mm diameter steel columns filled with concrete.

Paradoxically, their raking arrangement provides additional structural stability to the library hall above.

Energy-efficient environment

Despite its deep-plan library hall and fully glazed vertical block, the building is designed to rely on natural ventilating and daylighting for most of the year. Services engineer Battle McCarthy reckons that annual energy consumption in the building will be as low as 182 kWh/m2, and cost only £17 065 a year.

Skylights and north-facing glazing are designed to distribute daylight evenly throughout the building.

The building is cross-ventilated through opening windows and vents, with additional mechanical extract ventilation required in summer. No artificial cooling is needed, as the exposed concrete frame absorbs excess heat. Added to that, little solar gain is expected in summer, as the five-storey window wall faces north, and the south-facing glass facade is shaded by the projecting library hall. Not least, the library hall is ventilated and cooled by a natural stack effect that draws cool fresh air from the shaded void directly below and out through rooftop vents. The clerestory windows to the African-Caribbean pod are shaded by the rooftop beret with its peak projecting southwards towards the sun.

The vertical block's extensive windows are of low-emissivity double glazing panels to provide good thermal insulation.