No 4 The Square, part of the landmark Stockley Park development near Heathrow Airport, was found to have structural faults during final checks by Arup Associates in November. Remedial work is being carried out and will be paid for by Arup.
Andrew Vander Meersch, chief executive of client Stockley Park Consortium, said Arup told him that the £10m speculative office had defects that could cause its extensive glass cladding to shatter in high winds.
Vander Meersch said: "Arup said there was a problem and it would put it right. It's a pain and rather annoying, but Arup is putting its full machinery into it and it doesn't stop us marketing the building." He added: "I'm not picking up the tab. Arup will pay to rectify the problem; it's not costing me a bob."
Costs to rise above £500 000
A spokesperson for Arup parent Ove Arup Partnership refused to say how much it would cost to rectify, but director Richard Haryott said there will be "quite a cost".
A structural and cladding expert put the figure at £500 000, but said it could cost a lot more, depending on how much of the building's glazing system had to be removed.
The Arup spokesperson confirmed that a member of the project design team had left the company but denied that his departure was related to the troubled building.
The problem stems from the fact that the steel framework of the circular building was deemed too lightweight to support the building's glazed envelope.
Clashing glass panels
The effect of this is that the building could be susceptible to movement in gales. In turn, this could cause its exterior glass panels to come into contact with one another and make them shatter.
Haryott said: "There was a possibility of the gaps between the glazing panels closing, causing the panels to touch, so we agreed a programme of works to put it right, which should be completed by the spring." Haryott said that the gap between the glazing panels was originally wider but that it was reduced to guard against water penetration.
He said: "It's a complex issue and there is a chain of reasons why it's got to this stage. It's a very complicated situation." He added that the structure of the building would be stiffened by replacing or reinforcing the columns.
He said that the panels would be repositioned to increase the gap between them, but he was unable to say whether this would involve removing all the glazing. "We may just remove strips of glazing rather than all of it," he said.
However, the structural and cladding expert said: "Options for strengthening the columns in a circular building of this sort are limited without removing most of the glazing. If you have to do that you could be talking a good deal more than £500 000 to put it right. You could be talking over £1m."
