Revealing its structure under a continuous glass skin, the building that dominates the roundabout of Holborn Place has a clear convex volume, returning the typically saturated image of this pivotal area between the City and the West End of London.
Designed by Lord Norman Foster, the building has eight levels for flexible office desks.
Among the different types of facades designed for this project, the main façades concern two systems that stand out from the crowd: the large entrance atrium (curtain walling and glazed roof) and the lateral offices cladding.
Entirely glazed and resting on an imposing structure made of steel tubes, the central Atrium houses the lobby and provides additional natural light to the offices, via an atrium facade. Note that this space accommodates one of the largest glass and steel tie-rods staircases ever made (70 tons).
The vertical face, 1500 mm wide faceted curve, consists of non-insulating glass volumes carried only on horizontal cross-beams every 3800 mm, without vertical profile (butt glass with silicone seal).
The core of the horizontal crosspiece is composed of a steel plate hooked to the tubular frame. This steel core is clad with a "structural" aluminum profile that supports the glazed units, receives the seals and fixes the outer covers. Finally, two aluminum half-cover profiles complete the interior finish of the transom.
The glazed roof uses glazed units assembled on a mullion-transom system developed especially for this project.
On both sides of the curve of the Atrium, the (exterior) facades of the offices are made with stacked elements of 1'500 mm wide by 3'800 high, entirely prefabricated in the workshop, including the interior facing stone.
Each element consists of a single crimped frame, which receives on the outside face a glazed unit bonded by "Structural Glazing". On the inside of the elements, a few centimeters behind the glass, are fixed granite facing pieces, to mark the structural lines of the construction (slabs and pillars). Most of these facing stones are already laid on the prefabricated element in the workshop. To preserve access to the fasteners, the last stones were fixed on site after the elements were installed.