A year later, however, and the roof is a sorry sight. Scaffolding prevents visitors from venturing on to some areas, and cracking mars the glazed panels. Inside the centre, leaking water has scarred the wall of the glass-making factory with rust-coloured streaks.
The problems are so bad that Kvaerner, which built the centre, has returned to carry out repairs. And the roof's designer, Arup Facades, has prepared a report on its problems.
The centre's glass roof was the first to be designed specifically to be walked on. The architect originally intended the roof's glazed surface to stretch over 75% of its area, but cost restrictions reduced it to roughly half of this, and concrete paviors make up the remainder of the surface.
The first clue that all was not well emerged when cracks started to appear in some of the glazed roof panels during the building's construction. A total of 11, 1.2 m2 panels were replaced by Kvaerner during construction. At the time, the damage was thought to have been caused by workmen on the roof.
By the time Prince Charles visited the centre in October 1998, a further 16 glazed roof panels had been replaced. This time, the finger of blame was pointed at local children, said to be damaging the glass with their skateboards.
Now, almost a year after its opening, cracks have again appeared in some of the panels. But Geoffrey Woodcock, the glass centre's project manager, says the building's closed-circuit cameras have not produced the expected evidence convicting the skateboarders. Nor is there any proof that the roof has been deliberately vandalised.
Meanwhile, Kvaerner has replaced many of the polysulphide weather seals between the roof's glass panels in an attempt to stanch leaks in the roof. Tape plastered to the outside of some joints highlights the areas the contractor has yet to work on. Kvaerner reports that this work is now 90% complete.
The contractor has also been involved in stopping leaks around the two furnace chimneys and at the junction of the roof's glazed area and the concrete section.
While Kvaerner is still on site, debate rages on about why the roof has failed. The Commission for New Towns, owner of the site's freehold, is administering the defects building contract. It says: "Our consultant engineers believe the cracks are due to impact from outside sources, but there is the possibility that they may be due to thermal movement. We are waiting for the results of our consultant's report." Kvaerner, too, says the cracked glass is "all the responsibility of the user, deemed to be down to impact damage by persons unknown", and seems to think there has been some movement in the roof. "The mastic had to be replaced in some areas because of movement," said a company spokesperson.
Architect Andy Gollifer is ducking the row. The roof is "a horizontal facade that Arup Facades designed", he says, adding, "It's irritating when things like this happen." Graham Dodd, a designer at Arup Facades, has investigated the problems and compiled a report for the Commission for New Towns. He says: "Thermal movement is the least likely reason for the cracking." But he was not prepared to disclose what he does consider the most likely reason.
Geoffrey Woodcock, project manager for the glass centre, thinks the impact damage is so minimal in the vicinity of the crack that it could be the result of something as minor as a stone trapped in the tread of a shoe. This view is supported by the presence of cracks only in the top layer of the 36.5 mm thick, four-ply heat-toughened laminated glass panels. Experts have criticised the glass specification. One source said that toughened glass would have had more resistance to impact damage than the heat-treated glass used. Dodd counters this, saying: "Toughened glass is more satisfying to vandalise. It's no more resistant to impact damage than heat-strengthened glass, and when it does break, it shatters." The Commission for New Towns says the cracks do not present a safety hazard, explaining that the glass panels have only been replaced for cosmetic reasons and not because the cracks affect their structural integrity. But Dodd admitted that "once cracked, the heat-treated glass would not be as strong as if it were not cracked".
Kvaerner is racing to complete repairs before the defects liability period for the centre ends on 31 March. "We'll be 99% complete, although some of the repairs are weather-dependent," said Kvaerner project manager Robin Gates.
But the client expects a delay in correcting some of the defects, as repair work will have to fit around the glass centre's timetable. The cost of replacing the panels has been put at £20 000 so far.
