The transformation of the Reichstag is rooted in four related issues: the Bundestag's significance as a democratic forum, an understanding of history, a commitment to accessibility and a vigorous environmental agenda. As found, the Reichstag was mutilated by war and insensitive rebuilding. The reconstruction takes cues from the original fabric; the layers of history were peeled away to reveal striking imprints of the past - stonemason's marks and Russian graffiti − scars that have been preserved as a 'living museum'. But in other respects it is a radical departure; within its heavy shell it is light and transparent, its activities on view.
Public and politicians enter the building together and the public realm continues on the roof in the terrace restaurant and in the cupola, where ramps lead to an observation platform, allowing people to ascend symbolically above the heads of their representatives in the chamber. The cupola is now an established Berlin landmark. Symbolic of rebirth, it also drives the building's natural lighting and ventilation strategies. At its core is a 'light sculptor' that reflects horizon light down into the chamber, while a sun-shield tracks the path of the sun to block solar gain and glare. As night falls, this process is reversed - the cupola becomes a beacon on the skyline, signalling the vigour of the German democratic process.
The building provides a model for sustainability by burning renewable bio-fuel - refined vegetable oil − in a cogenerator to produce electricity: a system that is far cleaner than burning fossil fuels. The result is a 94 per cent reduction in carbon dioxide emissions. Surplus heat is stored as hot water in an aquifer deep below ground and can be pumped up to heat the building or to drive an absorption cooling plant to produce chilled water. Significantly, the building's energy requirements are modest enough to allow it to produce more energy than it consumes and to perform as a mini power station in the new government quarter.