City Hall, Greater London Authority Headquarters - 2005

City Hall houses the assembly chamber for the twenty-five elected members of the London Assembly and the offices of the Mayor and staff of the Greater London Authority. Building on the techniques explored in the Reichstag, it also expresses the transparency and accessibility of the democratic process and exemplifies a sustainable, virtually non-polluting public building. Its tilted form ensures optimum energy performance by minimising the surface area exposed to direct sunlight. Analysis of sunlight patterns throughout the year produced a thermal map of the building’s surface – this is articulated in the cladding. To the south the building leans back so that its floor-plates step inwards providing shade for the naturally ventilated offices. The building’s cooling systems utilise ground water pumped up through boreholes from the water table. Overall, City Hall uses just a quarter of the energy consumed by a typical air-conditioned office building. Energy-saving techniques such as vents that can be opened for natural ventilation, borehole water cooling, heat recovery and use of a thermally efficient façade mean that chillers are not needed and for most of the year, the building requires no additional heating.