It's a hard life

Terry Farrell claims his design for the International Centre for Life in Newcastle is foetus-shaped. Locals have dubbed it "the Leaf", and Laing, the contractor building the £18.5m genetics visitor centre and biomedical laboratory, is calling it every name under the sun.

The reason for the name-calling is that the centre's roof, with its complex, asymmetric shape and mix of materials, is proving difficult to construct. Work on the interiors is scheduled to start before the end of the month, and the roofing contractors are scrambling – two months behind schedule – to ensure the roof is watertight.

In fact, the roof of the genetics visitor centre is the most stunning feature of the £58.5m, two-phase millennium project that celebrates Newcastle's links to genetics and molecular biology. Phase one is a five-storey, £13.5m business centre for biomedical companies that Laing completed last year.

Whereas phase one was a relatively straightforward render-clad office, phase two features a concrete-framed laboratory building that will be used by Newcastle's university and hospital researchers, and a visitor centre comprising a steel-framed box and a glulam-supported, irregularly curved roof that stretches from the rafters of the box to the ground. Topped with pre-patinated copper cladding, the construction will look like a giant leaf lean-to when it opens for Easter 2000.

Laing knew the roof would cause problems. When bidding for the £18.5m, phase two shell-and-core contract, no fewer than 20 provisional sums were included – a huge number for the size of the contract. The problem, says Laing, was that the client was keen to see it start on site, but the design was not terribly well advanced. Dr Cliff Jessert, the Centre for Life's project manager, explained that the centre's complex funding arrangements are linked to project milestones, so a later start on site might have meant forfeiting some funding.

Laing's difficulties began immediately. The outline of the building is curved, but not in a regular way. The radius is shorter in some places than in others, so setting out the supporting wall that the lower edge of the leaf sits on was a nightmare, says Stuart McArthur of Laing Northern. To compound the problem, the wall tapers up and had to be constructed in 18 m long facets.

The next challenge was setting out the tubular steel roof supports. The upturned tripods were designed by project engineer Mott MacDonald and manufactured and installed by steelwork specialist Westbury.

Because of the shape of the roof, all the tripod legs are different lengths, and so placing the tripods in exactly the right position was a tough task that required constant surveying.

The tubular steel structure supports nine primary glulam trusses that are hinged to the steel box at one side and to the concrete wall at the other. The eye-catching metal hinges are required to allow for movement caused by settlement and wind. "The glulam will move 30 mm under its own weight and up to 70 mm in strong winds," says McArthur.

The glulam beams were covered with a layer of 10 mm thick plywood, a vapour control barrier, a 150 mm thick layer of insulation, a layer of 18 mm thick plywood, underlay and finally a 0.7 mm thick standing-seam pre-patinated copper roof. Taking the glulam beams into account, the roof layer is a massive 700 mm thick.

Building up so many layers of materials around irregular curves has tested the skills of the contractors, and required constant checking by the architect. But with time and cost pressures mounting, the specification has suffered. Secondary glulam trusses that overhang the distinctive tubular steel "stalk" of the leaf were intended to support glazing to create a giant canopy. The glazing has since been dropped from the specification, which will leave the curious spectacle of glulam beams jutting out from under the roof's edge.

The project is proving tough to handle, but Laing has worked seven days a week to catch up with the schedule and is confident the project will meet the client's deadlines. Project manager Dr Jessett – a former Ove Arup & Partners geotechnical engineer – is happy with Laing's performance, and has awarded it £2m to manage the £10m interior fit-out contract for the visitor centre.