GLA headquarters, London
GLA headquarters, London
Foster’s design for City Hall, the new headquarters of the Greater London Authority, is a one-off in every sense of its architecture. This is a 10-storey building containing various offices, a large entrance foyer open to the public and the rooms for the city council on the fifth, sixth and seventh floors. The offices of the Mayor of London are situated between those floors and the “democratic” culmination - something with which we are already familiar from Berlin’s Reichstag. Situated directly on the south bank of the Thames, the particularly fascinating characteristics of this building are its round outline and uniquely structured glass envelope. The building’s spectacular form is the result of energy studies carried out to optimise the summertime thermal performance and also the amount of incoming daylight for illuminating the working zones in the building.
Especially striking is the “lens” above the main entrance - by seele. An insulating glass façade comprising 730sqm of structural glazing optimises the amount of daylight reaching the atrium inside. A three-dimensional, curved steel frame of 323mm dia. circular hollow sections spanning up to 25m forms the primary structure. Some 80% of the horizontal main steel members are filled with water in order to condition the interior climate and prevent condensation.
Mounted on the triangular bays of the primary steel structure is the secondary structure of welded steel T-sections which divide the façade into triangular panels (base length approx. 1.7m, height max. 4.5m). As the façade gradually curves further and further back over the height of the building, the dimensions of these panels change constantly; repetitions occur only as a result of the symmetry of the building about a central vertical line. A high-performance coating plus ceramic screen printing, increasing in density with each storey, together regulate the solar gains.
Especially striking is the “lens” above the main entrance - by seele. An insulating glass façade comprising 730sqm of structural glazing optimises the amount of daylight reaching the atrium inside. A three-dimensional, curved steel frame of 323mm dia. circular hollow sections spanning up to 25m forms the primary structure. Some 80% of the horizontal main steel members are filled with water in order to condition the interior climate and prevent condensation.
Mounted on the triangular bays of the primary steel structure is the secondary structure of welded steel T-sections which divide the façade into triangular panels (base length approx. 1.7m, height max. 4.5m). As the façade gradually curves further and further back over the height of the building, the dimensions of these panels change constantly; repetitions occur only as a result of the symmetry of the building about a central vertical line. A high-performance coating plus ceramic screen printing, increasing in density with each storey, together regulate the solar gains.
The expansion joint between adjoining façade sections is formed by a continuous plastic-coated sheet metal channel. Together with the “lens”, the primary structure of the roof, constructed in the same way, contributes to the overall stability of the building. Rooflights with fixed glazing, insulating glass opening lights for ventilation plus access to service areas enable the “triangular architecture” to continue across the roof. Simultaneously public and “private”, the atrium takes on a special significance, and was the second contract awarded to seele. Being seen to be working corresponds to today’s idea of democracy; however, being able to work undisturbed is still essential. Despite the all-glass design, the high acoustics and fire resistance demands have been met. Conceived as an open interior space without intervening columns, the tapering glazing to the atrium called for a whole series of tailored solutions. The suspended floors are supported on a concrete service core in the centre of the building and cantilever out from this, in the atrium fixed only at the façade. “Funny static movement” is the name given by the project team to the ensuing movement of the gallery: max. 40mm downwards and 15mm upwards in the centre. To compensate for these movements, the panes of glass, glued to metal frames, are fixed on one side and fitted into a sliding joint on the other. With the help of a special sealing strip developed by seele, the vertical joints, which are subject to especially intensive movement, are not obtrusive.
