The irreducible element -- the quest for total efficiency.

Inspired by nature but brought into being by technology, the quest to enclose the greatest area with the maximum structural efficiency has reached new heights of spatial and tectonic drama.

When you look at the extraordinarily ingenious design of the Frankfurt Messehalle -- the largest space of its kind in Europe, covered by a single, column-free folded-plate roof arching lengthwise - you are looking at the latest manifestation of a continuous line of architectural thinking. Designing the maximum enclosed area with maximum efficiency has always been a trademark of Nicholas Grimshaw & Partners. In the early days, this quest was driven by the need to design new kinds of low-cost, adaptable industrial space -- bringing architecture to the previously design-resistant zone of the edge-of-town distribution warehouse. Later the principle - each time with significant - variations - was applied to an ice rink in Oxford, a newspaper printworks, and a supermarket in London. Then came the bravura trainshed of Waterloo International, which in turn led -- unexpectedly but logically -- to the structurally minimalist domes of the Eden Project in Cornwall. At the start of the twenty-first century, therefore, thi s process of steady evolution has reached a point where the spatial drama of the buildings is attaining a new level of ambition.

The larger the contained volume for a given area and weight of structure, the more efficient the building. The soap bubble and the spider's web are perfect examples of structures that are irreducible -- just exactly as strong as they need to be, impossible either to add to or subtract from. Many architects work towards such an irreducible minimum of structure, but few have taken it to such extremes as NGP. Their two largest enclosures at present under construction, Eden and Frankfurt, represent respectively the soap-bubble and spider's web approach to the problem.

While it can be argued that Waterloo International in 1993 represented an extreme refinement of Victorian trainshed technology at the interlinked glasshouses of Eden wrapped around the sides of a former china clay pit things have moved on. NGF worked with the same engineer, Anthony Hunt Associates, and at first tested a Waterloo-type truss structure. They soon abandoned that approach in favour of a lightweight arrangement of geodesic domes, glazed with inflated triple-layer pillows of ETFE foil rather than glass. The structural shift not only allowed the building to adapt more readily to the contours of the site, but also resulted in a much more delicate structure of hexagonal cells. The design of the superstructure and envelope was then developed and refined with Mero Systems.

There has been enormous interest in the construction of Eden -- indeed, it is unique among British Millennium projects in attracting large numbers of paying visitors who come just to see it being built The structure weighs less than the forest of scaffolding poles that was erected to build it It has a fragile quality Enclosed, the domes are indeed like soap bubbles - or to explore another metaphor, like an insect's compound eye (something of this effect, though achieved by different means, is apparent in the giant 'eye' over the concourse of the unbuilt Pusan Bay transport interchange in Korea). Whereas a standard Bucky dome is perhaps an over-familiar object, at Eden the intersection of domes of differing sizes gives the complex a unique architectural quality As with so much of NOP's work, there is an accretive sensibility to the arrangement of internal and external spaces.

In contrast, the Frankfurt Messehalle is a classically symmetrical temple of display There was the given area, there was the two-storey volume to be enclosed. It is by far the largest big shed the practice has ever done. The novel solution chosen for the roof--this time working with Ove Arup and Partners -- is a single giant folded plate structure formed from a continuous network of welded steel tubes spanning 165m. This is a spider's web rather than a soap-bubble solution. The roof is as lean as it could possibly be and performs many jobs at once. It is lower than a more conventional arched structure -- which means the volume of air to be treated is less, but still contains high individual air reservoirs, vital for passive ventilation and smoke control. The total available area for acoustic absorption is maximized by the undulating and twisting inner surface. However, with the structural tubes half-covered by the inner skin there are no upward facing surfaces that could collect dust, a vital point in such a large hall.

In another setting, this would be not an exhibition hall but an airport terminal or transport interchange. One can see similarities for instance, between the Frankfurt Messehalle and another project about to start construction, the new main terminal or Flughafenkopf for Zurich Airport This is an ordering device: the big roof, originally conceived as an undulating form very reminiscent of a pair of spread wings, was refined into a simpler, scimitar-shaped form, 250m long, which ties together many of the existing buildings and activities of the 50-year-old airport It looks very simple: in fact the re-ordering of the airport, including the creation of new road, bus, tram and rail transport interchanges, plus a large retail centre, is highly

complex. The clarity of plan, however; means that it will not seem that way

The Grand Stand at Lord's Cricket Ground can be described as 'pure structure', its roof trusses suspended symmetrically in the manner of a suspension bridge. However, the practice is increasingly beginning to use structures for other ends as well. For example an unsuccessful competition entry for an enclosed baseball stadium in Seoul has a tilted asymmetrical roof structure which gives the vast internal space a direction. The tilted steel arches of the ljburg bridge in Amsterdam were conceived to created a pair of outdoor 'rooms' marking the transition from old land to new. The roofs of the Bijlmer station project (also in Amsterdam and designed in collaboration with the Dutch firm Arcadis), incorporate a diagonal fault line' at the point where a grand new boulevard is due to run beneath. This creates an architectural focus over the station's front door below. Here it was not possible to build one huge vault across eight tracks, since the work has to be phased and the existing station must remain in operation during construction: but supporting each set of roofs individually allows a different set of design freedoms.

It is perhaps surprising that a set of such very different large-enclosure solutions should each seem somehow to be inevitable. Although there are assonances between projects, there is clearly no one-solution-suits-all formula. Always, the components are made to work hard, generally performing several tasks at once. In each case, however, you would have to search very hard indeed to find a single extraneous element.