Pure and simple: Sauerbruch Hutton's headquarters building, for Germany's Federal Environment Agency, is a model of integration.

What thoughts must have crossed the minds of Sauerbruch Hutton when they won the competition in 1998 to design a new headquarters from Germany's Federal Environment Agency (Umweltbundesamt/UBA)--in Dessau? How much would the Bauhaus (a short walk away) and its history impinge on the minds of the designers?

Matthias Sauerbruch addressed the issue in a 2002 lecture, 'Modernism without dogma'. He noted that whereas the Bauhaus had concerned itself, in broad terms, with the unification of art and technology, the UBA stands for the symbiosis of technology and nature. The Bauhaus discounted the relationship of buildings to nature, wilfully ignoring the effects of sun by providing a giant single-glazed window facade facing west not north: 'The self-confident geometry of the building and its prismatic purity communicated ... unbroken dominance over nature (which, as we all know by now, has a purely rhetorical character, as the building is in a permanent state of decay.)'

For Sauerbruch Hutton, the Bauhaus served as 'model and warning'. It celebrated an extraordinary combination of artistic impulse, desire to build, and a truly impressive attitude to production (the entire project was designed and built in 18 months). Yet the project was flawed by 'the contradiction between standardisation/mass production on the one hand, and artistically inspired craftsmanship on the other', which resulted in very limited use of standardised construction, and hardly any industrial prefabrication. It makes the construction programme look even more impressive.

Sauerbruch suggested that despite the many and obvious differences between the Bauhaus building and the UBA headquarters, they generally stem from changes in the context in which we live, rather than a fundamentally different design spirit. (Reviewing SH's work to date, it would be hard to think of a practice more committed to the integration of colour, art and architecture, just as much in commercial buildings as in more obvious cultural situations, surely in the Bauhaus spirit.) He believed the connection between rationality (technology and planning) and sensuality (in materials and production), plus the integration of a large spectrum of aesthetic expression was exemplary: 'This dimension of real integration constitutes a quality that has more or less been lost in the meantime and which our generation has to re-acquire'.

Integration was of course a keynote of the Weimar Bauhaus; Kenneth Frampton quotes from its 1919 Proclamation in his Modern Architecture, a Critical History: 'Together let us conceive and create the new building of the future, which will embrace architecture and sculpture and painting in one unity ...' It is an aspiration which has recognisably informed the new UBA building, opened to great acclaim in May this year, though one might say that integration has been taken several steps beyond art and architecture. Quite apart from aesthetic elements, this project (known as the 'snake') synthesises ideas about regeneration, landscape and the city, energy consciousness, mixed-use, community use and urban design in a joyful free-form expression rarely found in that generally banal typology, the government office building.

The regulatory authorities in the former East German town must have been startled by the architecture presented to them. Without close scrutiny, it would be hard to guess that the offices (for 800 workers in ten departments) are cellular standardised units, mostly of about 12 square metres to conform with public sector requirements in Germany. Laid side by side, the conceptual diagram for the building could have been a 600m long office terrace plus corridor; the competition design proposed a four-storey curved building of about 460m length, with the offices placed either side of a central corridor, and a tree-like circulation route. Apart from the flowing nature of the plan, the authorities were certainly surprised by the idea that the entire site would be accessible to all, and as a public route. No security fencing! But the real surprise, unless they were familiar with SH's previous work, would have been the bold colour palette used on the exterior (more restrained on the interior).

There is absolutely nothing arbitrary about the way in which colour has been deployed on this project. A key purpose is to break down the potentially monolithic nature of the facade, while providing a colour code for seven different areas of the building, each of the seven sets of colour related chromatically to its neighbour. The facade, which is 35 per cent glass, has eight alternating horizontal bands of timber and glass. Spandrels are clad in larch slats, which will weather to silver-grey. Clear glazed windows are set back 30cm from the timber; in between a series of glass 'blocks' of varying widths are inserted, with screen-print colour enamelled onto the back surface. In addition, the reveals of the coloured blocks have been treated with contrasting colours.

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Internally, colour slides in and out of the facades in an entirely rational way, widths varying according to the percentage of glazing. In the 'Forum' entrance foyer, both external and internal facades appear. Complicated to explain, but once you are in the building you begin to understand how all this works, and to appreciate the subtlety both of the colours and the thinking behind each element of the completed design. This is a big building (nearly 40 000sqm) which has been packaged into more comfortable (colour-coded) elements, the whole brought together by the splendid curving atrium with multiple bridge links; it incorporates an auditorium and library (the latter a restored, upgraded and expanded old building), while cafe, which is open to the public as well as agency workers, is placed separately on the site as two pieces: a brick 'garden-wall' kitchen element, and a glazed pavilion looking across landscape to the offices.

The site plan in part derives from a landscape proposition going beyond the building plot. It also relates to the surviving small Worlitzer Bahnhof, becoming an information centre, which provides an end stop for the new complex, but originally marked the division between industrial town and countryside beyond, in particular the Worlitz Garden, created in the English eighteenth-century style. A freeform arc of 'landscape in the city' connects the area in front of the main Dessau station (1 hr 20mins to Berlin, where many of the agency staff currently live) to the residential area beyond the new complex, with the new cafe providing a small plug on one side, the office complex a bigger complement opposite. The implied landscape flows into the Forum of the offices, with a variety of carefully considered planting extending the idea of natural infiltration. It is all a long way removed from the industrial uses of the area on which the agency now stands, which from the late nineteenth century were based round the gas industries. Industrial uses, with concomitant pollution and ground contamination, continued into the 1990s; 1940s bombing resulted in post-war rebuilding. Part of the UBA move has involved a five-year ground water purification programme; no stone left unturned.

As you would expect, the environmental brief from the client, was about as rigorous as it could get. The task was to produce a building that would perform, in energy terms, 50 per cent better than one which would meet current regulations. Energy consumption was not to exceed 30-kilowatt hours per square metre per year. All materials were to be assessed from an ecological and biological point of view (which resulted in materials from aluminium to zinc being excluded; no plastic is visible in the building). The architects had to specify materials and products which were entirely ecologically correct: Russian larch was excluded on the grounds that the same type could be bought from Bavaria, involving fewer transport miles. Energy-saving measures had to show that they would provide payback, admittedly over a 50-year period. However, no special cost allowance was made for any of this; in fact the building came in under the budget of [euro]68 million, which was based on the standard cost per square metre of a German government building.

The green credentials of the complex are not advertised in a crudely exhibitionistic way. The renewable energy elements are largely hidden, including use of landfill methane for district heating, a geothermal heat exchanger--air inlets are masked by artworks--plus solar-assisted cooling plant and photovoltaic systems. All this produces about 20 per cent of the required energy to run the building, which is largely naturally ventilated. Offices all have opening windows, although on the west facade they cannot provide primary ventilation, while night ventilation is managed via electrically powered panels which can be controlled in respect of timing and temperature. The thermal mass of the reinforced-concrete frame, with exposed ceilings, helps.

What lessons does this complex hold for clients and designers with a less prescriptive agenda? One is that organisations that by definition are obsessive about environmental issues, find it difficult to take risks. Here the architects were not allowed to use recycled concrete, or vegetable oil as fuel, because the UBA has not yet sufficiently tested either to be certain they are appropriate. Another lesson might be that being truly tough on materials and products from a particular viewpoint excludes quite significant materials, whose manufacturers would no doubt be able to mount vigorous arguments as to why they too are ecologically correct. A third is that designing to meet the highest requirements for environmentally correct buildings does not necessarily involve a price premium.

Perhaps most important for Dessau is the growing contribution the building will make to the regeneration not just of this blighted site, but to the city as a whole. With one of the highest unemployment rates in the country, at 40 per cent-plus, the psychological impact of such a significant federal investment will be considerable. And of course there is now an additional reason to visit Dessau.

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