Mixing valves -- new ways to work.

Economic and social change has given rise to new types of workplace, a dynamic that the practice has explored and redefined through an innovative series of commercial projects.

The once yawning gap between the design of owner-occupied office buildings and speculative office buildings has closed somewhat, but there is still a way to go before the quality of working environment in each can be compared directly. It was not until the 1990s that NGP became involved in large-scale 'pure' office projects of either type -- until then its forays into offices had tended to be as parts of larger complexes such as factories or distribution warehouses. When the opportunity arose, the practice's immediate response was to attempt to reinvent the genre, blurring what it saw as increasingly irrelevant commercial distinctions between types.

The signs were there in the Western Morning News headquarters of 1992 with its aircraft carrier appearance, curving external tusk outriggers supporting the glazing, and a large, social staircase in the central atrium: not your average office block. That still had a factory attached, in the form of the printing press hall. But immediately afterwards came the RAC Regional HQ outside Bristol, completed in 1994. Something different was evolving there, a radiused triangle of a building on plan that was as much to do with accidental meetings of people on stairs or in the cafe as it was to do with organizing people at their desks. Again, the grand social space at the centre is the key to the building's plan. Grimshaw talks of 'mixing valves' when he describes such spaces, implying that he sees the movement of people around the building as a matter of fluid dynamics.

At the RAC building. people enter at the middle floor which means they have to move only one level up or down to their destination. The stairs and generous triangular landings spanning the atrium -- reminiscent of the 1940s staircase experiments of Berthold Lubetkin -- thus become more important than the lift cores. A certain romanticism is apparent in the positioning of a meeting room high in the air on twin masts, giving views of the motorway network for miles around: for this is principally a call centre, which could just as easily be underground or even in another country. But that is to miss the point, which is that the building is a symbol clearly visible to motorists, not vice versa.

Social mixing valves are much in evidence at Ludwig Erhard Haus (LEH) in Berlin. This includes -- and places on public view -- the tiny Berlin Stock Exchange, but it is primarily office space for financial services companies, plus auditoria and a club. One of the startling things about the building is not so much its unique armadillo-like shape, as the way it has acquired a use never originally foreseen: as a party venue, and not only for its occupants. Its long foyer running the full length of the street frontage just inside the marching row of robot feet supporting its structural hoops, has proved to be an enormously popular events space: as have the twin asymmetrical atrium slots with their aluminium sarcophagus-like lift cars. It is fair to say that the average office block is not usually regarded as a crucial party destination, let alone the setting for a fashion shoot.

Much the same social plan form as LEH is to be employed for an otherwise utterly different NGP building, the Donald Danforth Plant Science Center in St Louis, Missouri. This, the practices first building in the USA, combines laboratories, offices, and a publicly-accessible three-storey garden atrium, all enclosed by a sophisticated climate-controlling skin. The laboratory blocks within the overall envelope are linked by walkways, bridges and meeting platforms. These are devices to extend the concept of the working environment out of the individual cell or office floor into another kind of space where happenstance plays more of a part. The idea of the building envelope as a relatively loose container within which other architectural forms and spaces can occur, is a growing trend in NGP's work, to be found also in its science-related Millennium projects in Birmingham (Millennium Point) and Leicester (National Space Science Centre).

Speculative City of London office buildings are, however, another beast entirely. London's financial centre traditionally consists of enclosed, private fiefdoms, while the speculative block usually contains very little social space outside the standard floorplates. NGP now has planning permission for two City office buildings that propose different solutions to this problem. At St Botolph's, in the east of the City, an understated facade curving round the perimeter of its city-block-sized site will contain a working population of 5000. Usually, there is nowhere for everyone to meet in such buildings. Here, there is to be a unique underground amphitheatre, directly accessible from within the building with a glass-sided taxi bridge spanning over it at one end.

This is very different from the other NGP city project, an office building on Gresham Street known in the office as 'the tree house'. There, the aim is to acknowledge the delightful adjacent churchyard of St John Zachary with its mature plane trees. Two finely detailed facades of overlapping green Cumbrian slate panels flank a U-shaped atrium which embraces the gardens while office wings to either side are suspended over a column-free cloister-like entrance hall. The open-sided atrium base is stepped back to form a ziggurat of landscaped terraces, bringing greenery into the heart of the building both horizontally and vertically. It is hoped that this will encourage the building's occupants to linger and mix both on the glazed atrium lift bridges and on the ground floor.

NGP's office buildings continue to vary greatly in type: the little Mabeg building at Soest in Germany, for instance, raised high on its columns to allow the factory's lorries to pass beneath, is a showcase for the company's products as well as a working environment. In contrast, the Orange call centre in Darlington is a low cost building which outsiders very seldom get to see. But even there, in what is essentially a twist on the old Grimshaw notion of the refined industrial shed, the mixing valve is present. The restaurant for the whole Orange complex of buildings on the site sits on a central mezzanine level in the new building, so ensuring that there is constant interaction of people who would otherwise seldom meet. Call centres are too often the twenty-first century's satanic mills; but here the workers in this stressful business are given a dignified and humane environment. Finally, at the forthcoming Duisburg maritime services centre, a large oversailing solar shading canopy structure serves to define an interlocking sequence of waterside public spaces next to a future marina. This takes the mixing valve principle into the public realm and enables a humble speculative office to become a public destination.