Crystal clear.

This new office building for an advertising agency in Frankfurt is a refined statement of corporate function, expressive materiality and enlightened energy use.

As land becomes even more valuable resources the destiny and efficiency with which it must be used cannot in all cases be adequately served by mere adaptation of existing structures. Schneider + Schumacher started out with a commission to refurbish a factory, of no particular historic or aesthetic value, for office use but were able to convince their client that a new building constructed on energy saving, loose fit, principles would be cheaper to run, more adaptable to future ecological and technological requirements and therefore have a longer life expectancy.

The new six-storey building with underground car parking provides 5915 sqm of usable office space at a cost of 20 million DM on a 2366 sqm sites. Access to the building is across an inner courtyard covering the basement car park. The building is oriented east-west with its north elevation parallel to Hanauer Landstrasse, a very noisy and fast-moving thoroughfare running along the north bank of the Main, and its southern elevation overlooking two man-made port basins on the river. Construction took 20 months and the building was completed in early 1996.

At the beginning of the design phase the tenant was unknown so the architects concentrated on designing efficient but economically serviced flexible spaces. In the end the idea of a glazed shop-window image served both representational and technical requirements for a tenant involved in advertising and communication. Enclosed in a transparent envelope with two glass lifts the building publicises the company -- J.W. Thompson -- as it goes about its daily business and gives employees views to the water and harbour. depending on light and season the facades change colour and the hue like a chameleon.

The north facade, which faces the busy Hanauer Landstrasse, forms one side of a vertical six-storey high sound and temperature modifying air space within the building, 29.6 m high, 66.6 m long and 2.8 m wide. Within this `winter garden' buffer zone the main staircase runs parallel to the sheer fall of roof-hung insulating and security glazing. The structural specification for this crystal box facade reads like the instruction manual for a string puppet. Each 3.35 x 1.8 m glass sheet is clamped in a butt joint with its neighbour and hung on stainless steel cables running from ground to roof level. Wind forces are taken up by stainless steel props fixed back to the reinforced concrete structure. Glass sheets on the roof of the winter garden lie on a steel framework while smaller 2.8 x 1.675 m glass sheets, cladding the narrow sides, are connected by steel triangular props back to the concrete structure. Walking up the open tread main staircase with its slender steel horizontal balustrades, a bird's eye view of the city below to the left and successive open and glazed working the floors to the right, induces mixed feelings of weightlessness and vertigo. Everything is light and transparent, or solid but very slender, designed down to the minimum for maximum efficiency and elegance.

To protect against overheating in summer the south facade, in contrast to the winter garden, has heat reflecting panes set between 900 mm spaced vertical mullions. Multifunctional continuous balconies at every floor on this south elevation shade the facade, in contrast to the winter garden, has heat reflecting panes set between 900 mm spaced vertical mullions. Multifunctional continuous balconies at every floor on this south elevation shade the facade, provide maintenance access, escapes in the event of fire and hinder the spread of smoke and flames between floors.

The 450 mm circular reinforced concrete columns support exceptionally thick 300 mm slabs which, acting as time lag storage heaters, are plastered on the underside and carry raised floors. Within this double floor system, as well as recessed light fittings, electrical and multimedia cable runs, an air plenum serves floor mounted fresh air inlets. Heat gained from the used air allows a lower capacity heating plant to be installed for the running of hidden convector space heating units in the floors along the southern facade and the internal north-facing glass walls. Room temperature is designed to reach 20 deg C with an external temperature of minus 12 deg C. Spaces in the southern side of the building are ventilated by openable windows while the internal spaces have mechanical ventilation which expels air at roof level. All ductwork, heating pipes, boiler and pump have been so specified that it would be possible, with an additional roof mounted refrigeration unit, to convert to full air conditioning if required. At present the central heating energy source is natural gas but this could also be exchanged for a solar energy source.

Till Schneider and Michael Schumacher, who both studied in Frankfurt under Pete Cook, say they are crusading for no particular architectural style. However, their few projects to date, of which this building is their most refined, have all shown an ability to cut away extraneous detail, dissect, separate out parts, and lay bare simple form which makes function understandable. Simplicity achieved through complexity. Schneider + Schumacher are working with clarity and transparency in the steps of Gunter Behnisch and in the face of growing German architectural conservatism. Sustainable or ecologically friendly are only late twentieth-century expressions for a Modern Movement principle--appropriate building -- the paring down and efficient use of resources.

Other modernist features include the generous proportions of the reception pavilion, equating empty space with luxury, separately articulated and set at right angles to the main body of the building by a glass bridge connection, and the raising of the entrance floor above the ground with wide steps creating a sense of occasion. Environmental correctness can also be elegant.