The Great Court, London's British Museum

Designed by internationally acclaimed firm of architects Foster and Partners, the 6,100 sq. metre area is enclosed by a unique glazed roof, which has transformed the Museum's inner courtyard.

The Great Court is now a new visitor hub for the Museum and the development has also created a magnificent new civic space for London. At the heart of the newly developed area is the Museum's famous round Reading Room, now restored to its original glory and home to a modern information centre.

The newly created area is now entered from the Museum's principal level, through an impressive portico. Once inside, visitors can access information points, a bookshop and a café, and they can enter the museum's many galleries via a number of different entrances. Two broad staircases encircle the drum of the old Reading Room, leading to upper-level galleries and two mezzanine levels, elliptical in plan, which provide temporary exhibitions gallery and restaurant. Beneath the floor of the area are further new galleries, an education centre with auditoria for 350 and 150 people respectively, and facilities for school children.

To allow the Great Court to be used throughout the year, it is now totally covered with a stunning double glazed roof spanning 96 by 72 metres. The maximum height from the ground level to the highest point of the roof glazing is approximately 26 metres, and amazingly, the structure appears to have no visible supports to detract from the restoration of the classical façades around it. Instead, it spans the gap between the surrounding museum façades and the central drum of the Reading Room as a self-supporting structure. Despite its apparently delicate lattice form, the roof and its integral glazing system is very strong, and has been designed to be regularly accessed by appropriately trained personnel with all necessary cleaning and maintenance equipment.

Each glass panel is unique

Overall, the roof contains enough glass to glaze 500 average-sized domestic greenhouses. But despite its deceptive visual simplicity, every one of the 3,312 triangular double glazed elements is slightly different in size and shape because of the roof's complex geometric form. Individual panels vary in size between 800mm wide by 1,500mm long, up to 2,200mm wide by 3,300mm long, with an average panel area of approximately 1.85 square metres.

Each triangular shape varies too, the most acute angle between the sides of one triangular panel being about 15º, while generally, planar angles between glass panels vary from between nearly 0º to 30º. The most inclined slope on the glass roof is around 52º relative to the horizontal edges at the boundaries.

The total thickness of the individual insulating glass unit comprising each panel is 38.76mm. Each of these units consists of an outer 10mm thoughened Pilkington Optifloat™ Green which is separated from an inner pane of Pilkington Optilam™ by a 16mm air filled cavity.

The inner surface of the outer pane is coated with a 57% frit consisting of 4mm diameter ceramic white dots, which filters ultraviolet rays and substantially reduces solar gain. The inner, laminated pane consists of two 6mm sheets of annealed glass laminated with a 0.76mm PVB interlayer. This pane also features a Low-E coating on the surface facing the cavity. The unit structure results in outstanding strength and solar performance: overall, shading coefficient is about 0.26, energy transmission 0.23, light transmission approximately 30%, and U value 1.9 W/m2K.

Pilkington Optifloat™ glass was toughened, laminated and screen-printed in Germany by specialist glass processors Bischoff Glastechnik (BGT). International insulating glass unit manufacturer OKALUX then made up the 3,312 individual glazing panels.