The raised deck for occasional athletics events in Foster and Partners' and hok Lobb's £475 million designs for the new national stadium at Wembley will cost £15 million and take six months to erect every time it is used.
The scheme, launched a fortnight ago, features a temporary 6m-high raised platform engineered by Mott MacDonald. This will cover over two thirds of the lower terrace and pitch to facilitate athletics events - which was a condition of the £120 million lottery grant Wembley received. Uniquely, facilities for the event such as a warm-up track and doping control, will be catered for underneath the rigid deck. But although the project backers estimate it will be used only three times in 50 years, it will result in the loss of at least one England international because of the time it takes to build, and the additional £45 million cost will have to come out of gate receipts for the athletics events.
The massive new-look stadium has four symbolic, 130m-high masts in place of the twin towers, with an asymmetric catenary cable net and stayed trusses spanning 220m across the stadium bowl. A circumferential double compression ring or 'halo' around the stadium's upper terrace will be used to anchor the supporting cables and to transmit horizontal loads to tripod shear legs.
The old Wembley, said Foster, was plagued with cramped seats, columns spoiling views and the relatively long distance between fans and the action. The new seats are wider and deeper, offering more legroom, whilst the good things about the old ground - such as its atmosphere, the turf and the presentational route, would be retained. Similarly there will be better catering facilities, with over three times as many outlets, escalators to all levels, and five times as many wcs.
The roof opens up like a camera's exposure mechanism, said Foster, principally to allow the grass to grow - a problem in many stadia such as Ajax's in Holland. It should also prove useful in cutting down the shadowing effect that is problematic for televising events.
Foster was also keen to stress the building's 'green' dimensions - plans to line a section of the roof with photovoltaics and to use grey water, heat recovery and natural ventilation.
Wembley National Stadium chief executive Bob Stubbs refused to break down the £475m cost but said it included interest and inflation and that a planning application would be submitted in October. 'The cost will go down, not up,' he said. Wembley spokesman Chris Palmer defended the high cost of the development - against earlier projections of £320million, £155million less - on the grounds that the stadium includes revenue generators such as a Wembley visitor attraction, offices and a hotel. He added that the upper concourse was now enclosed and that capacity had been upped by 10,000 to 90,000. 'We're not building a Ford Escort here' he said. 'We're building a top-of-the-range bmw.'