Eco tower: glass towers are not necessarily eco friendly. This one shows how new architecture can be evolved from ecological and humane principles

Architectural Review, The, August, 2003 by Mary Gibbs

Murphy/Jahn's Post Tower dominates Bonn's former government quarter which forms the city edge against the Rhineside Central Park. Formally, the tower complements Egon Eiermann's Langer Eugen tower, previously for the civil service and now to be occupied by the UN, and Gunter Behnisch's parliament building (AR March 1993), which will become a conference centre now that the Bundestag has moved to Berlin. The long horizontal white strips of the broadcasting station Deutsche Welle by Joachim Schurmann & Partner (initially intended to serve the parliament building) complete a public campus.

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The new tower develops the best traditions of modern German office building. Most offices are for one to three people; all have windows and views over river and city. Energy efficiency and conservation are equally generative in the parti. Basically, the building consists of the 162m office tower and a four-storey semi-detached podium block containing auditoria and the larger meeting rooms.

In plan, the tower is an oval, split down the middle, with the two halves slightly shifted against each other. Connecting the two arcs of accommodation is the 7.2m wide vertical circulation and services core. In this, every nine storeys, there is the glass floor of a skygarden which acts as a communications level and vertical circulation crossover. Banks of glass lifts are in the middle of the skygardens, providing views and orientation.

Tower walls have a double skin of glass. The outer layer is a rainscreen and there are automatically regulated blinds in the voids between inner and outer layers of glass which are over a metre wide. The thermal mass of the building's concrete structure is called into play as part of the interior climate control system, using a cast-in pipe system that circulates water heated and cooled as necessary, partly using waste heat. Automated glass flaps in the rainscreens admit fresh air to the cavity to balance room temperatures; and air flow in the cavity can be mechanically assisted when necessary. Exhaust air from the offices conditions the climate of the skygardens, which themselves can obtain natural cross-ventilation through the louvred glass walls at their outer (east and west) ends.

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All these systems are integrated and controlled by a computerized building management system. The building cost, even with the computerized system and the double glass shell, is reckoned to be no greater than for a conventional sealed air-conditioned building, and operating costs are expected to be 60 per cent less.

Spatially, the building has the drama of the central voids and skygardens: often rather giddy-making. In contrast, the curved office corridors avoid the institutional feeling of so many German office buildings, in which the ruthless dominion of one-point perspective in the passages that serve the small offices induces a grinding institutional feel. Here, the single-banked corridors are luminous with daylight and their gentle curves prevent Kafkaesque sensations. What superficially appears to be yet another glass tower is in fact extremely thoughtful in human, cost and environmental terms.

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