Just so story.

The architectural effects of unification are not to be found only in the central area. The Ludwig Erhard Haus is an attempt to reposition Berlin as a major element in the German economy and to engage the public with business.

The Ludwig Erhard Haus(1) is across the Tiergarten from the mighty works on the east side of the park like the Government quarter (p50) and Potsdamer Platz (p32). But it too is a product of the decision to make Berlin the capital. Immediately after reunification, the Berlin Chamber of Commerce (to which all companies in the city are bound by law to belong) decided to help to try to make the city a great centre of business again? and bring all its activities together in a 'communications centre', where members of the commercial community could meet, the (very small) Berlin stock exchange could have its floor, and trade associations could take offices.

The Chamber had a rather grim '60s office block but wanted a bigger and much more welcoming and permeable building. So the organization decided to develop on a site round the corner on Fasanenstrasse, one of the rather dull nineteenth-century streets which run north from the Kurfurstendamm; it was originally lined with tenements containing flats over shops, and is now largely converted to offices. A competition was held. The winner was Nicholas Grimshaw & Partners, with a design that maximized the volume that the site was allowed to contain under Hans Stimmann's policy of critical reconstruction (p30), which on this site mainly meant insistence on an eaves height of 22m.

The Grimshaw firm started, like many other British practices of the '70s by building sheds. I do not mean to be dismissive in saying this. The big shed is one of the most important of the modern building types we inherit from the nineteenth century: repetitive, refined in detail, economical, capable of enclosing very large volumes, and even of nobility - at Waterloo station Grimshaw's built one of the very finest train sheds ever made (AR September 1993). The Ludwig Erhard Haus is a sort of cousin of Waterloo, in that it is an arcuated building made on an irregular site, so generating a very complex envelope geometry, curving in both plan and section. This is not the kind of form that sits easily in a street full of tenements, and Stimmann's planners demanded that there had to be a vertical street-front up to eaves height. Above and at the back, the curves of the arches are exposed under a stainless steel skin, though they are scarcely visible from the street (except at the ends).

The arcuated structure was adopted not just because the practice is used to such things, but because it enabled the maximum volume of accommodation to be got onto the site within the planners' envelope (p62). And it allowed a radical approach to urban building. Grimshaw was concerned to ensure that, as is usual in cities, lower floors should be capable of change - if necessary on a very large scale. Upper floors of the Ludwig Erhard Haus are suspended from the arches on steel hangers, so the bottom two stories are free of vertical structure. He points out that if the stock exchange, for instance, fails,(3) something as large as his Oxford ice-rink (AR March 1985) could be moved into the lower floors with no problems of fit. Even if such a big user could not be found, it would clearly be possible to divide the space up in all sorts of ways.

As they stand, the lower two floors are welcoming and open to the public. There is a long gallery on the street side, which is empty in these photographs, but actually often occupied by exhibitions, and even when empty is used by passers-by as a sort of arcade. On its inner side is a curved restaurant or cafe, welcoming under a balcony and frilly canopy. It is open to the public as well as workers in the various organizations on the office floors above and it offers rather a decent and inexpensive lunch in a street notably lacking such opportunities. Light enters the long space not just through the double-height glass wall on the street, but from the back as well, where two atria can be glimpsed through virtually free-standing lift structures.

The huge atrium spaces bring daylight into the middle of the plan because they are totally glazed from top to bottom on the curved (east) side. In effect, they are very big winter-gardens onto which offices can open their windows (openable office windows are almost a requirement in Germany these days). Atrium volumes are largely warmed by waste heat, and they are ventilated automatically on hot days by panes that open automatically at top and bottom of the glazed carapace.(4) The spaces as they now stand are pretty austere - grey, very solemn, very Berlin. The architects had proposed that they should be relieved by large trees, but as yet these have not materialized, partly because the client is unwilling to find the money, and partly because the atria are frequently used for exhibitions, when all their floor spaces (it is said) are needed for display. But the spaces are much livelier when you look back from the glass towards the middle of the building. The tall west walls are open screens, with small silver lift cars, and glass bridges to link their landings to the office wings on each side. The cars have cladding made manually by a coachmaker in the south of England, and their little rounded helmet-like forms whizz up and down, animating the spaces.

The offices themselves are in the slices of accommodation which define the atria, and in a strip which (until the curve of the upper part of the section is reached) runs along Fasanenstrasse. They are of course fitted out by the tenants, and as is usual in Germany, most are arranged either as conventional individual rooms(5) on corridors or as combi-offices (a mixture of such cells and group spaces). All offices look out either onto the street or an atrium. So that individual office windows can be opened, floor plates are comparatively narrow, and therefore quite small in area: this suits the client organization, which is determined to have many small tenants rather than one or two big ones to allow the building to serve a wide range of trade associations (it has already turned down one application for tenancy by a large firm).

In the base of the bigger atrium is an elliptical lantern over the dealing table in the stock exchange. You look down as if into a rock-pool to see the dealers who, when I was there, seemed as if they were moving in some sort of viscid liquid: activity on the Berlin stock exchange does not appear to be frenetic. The exchange is approached from the arcade which, in its spareness, is a cousin of the atrium volumes, but because of casual pedestrian traffic and exhibitions is more lively, and in summer, doors in the glass wall will be thrown open and cafe tables taken into the street. At the north end of the space, the floor is cut away to expose the lower level; an elliptical form emerges into the triple-height space so created. It contains the main auditorium of the conference centre with, on top, the dining room of a business club (which has a separate entrance). At the lower level, meeting rooms and the smaller auditorium of the conference centre under the pavement are approached along a cloister-like corridor which overlooks a pool.

Outside again in the street, the two generative forces of the building can be seen very clearly at its ends. The final arches(6) are completely exposed, free of the window walls behind, and covered in stainless steel sheets tensioned over curved formers by springs, so that the cladding remains crisp in all temperatures. Stainless steel sheets with traditional standing seams cover the concrete shells between the ribs, which themselves are expressed as ridges on the curved back of the building.

On Fasanenstrasse, the expression is completely different. An extremely precise vertical facade of white fritted glass automatically alters as the sun moves round, with sender louvres rising to act as glittering, emerald-edged solar shading, then fluttering back flush and crisp when the elevation falls into shadow (the white fritted glass is an outer screen; behind is a more conventional double-glazed wall with opening windows).(7) Below the smooth glass, which ends in a skirt to shade the arcade, the arches appear again as a row of silver-clad legs terminating in elegant stainless steel pin hinges: cushion-like feet, complete with claws - it is almost as if a lion has been crossed with a centipede.

An equally strange conjunction permeates the whole building when seen down the street. Berliners call it the 'Gurteltier' (the armadillo), and it is impossible not to recall Kipling's account of 'The beginning of the armadillos' in the Just So Stories: the first one, he says, emerged from an elaborate and not always easy fusion between a hedgehog and a tortoise. You can see the fusion between the arcuated building and. Stimmann's street architecture at a particularly strenuous moment at the corners where the front facade changes to the arches at the ends. It is certainly changeful.

And, maybe, it has resonance with Berlin. I have always been fascinated by the S-Bahn stations up on the elevated tracks: wonderfully bold metal structures, grey, direct and sometimes ungainly in their pragmatism. Just as the Ludwig Erhard Haus is a cousin of Waterloo, perhaps it is also related to the Hackescher Markt Bahnhof. Recent events indicate that the building may have other affinities with Berlin. The city has always been a bit wild when allowed to be so between its authoritarian phases. Of late, the Ludwig Erhard Haus has been hired out at weekends as a party location. As we go to press, its big arcade and atrium spaces have been so successful for enjoying yourself in, that streets round about have had to be blocked off to allow for many hundreds of revellers. P.D.

1 Ludwig Erhard was economics minister after the War and Chancellor between 1963 and 1966. The fantastic revival in German fortunes is generally held to be a result of his policy of Marktwirtschaft (market economy).

2 The big companies like Siemens, which grew up in the great Berlin boom at the end of the last century, moved their headquarters to West Germany from the islanded city after the War. Business is picking up again in the city, as firms like debis (p35) are located there (but the Daimler Benz headquarters remains in Stuttgart).

3 The big German stock exchange is of course in Frankfurt. And in any case, electronic communications are perhaps making stock exchange floors redundant.

4 The glass is cleaned by a wonderful specially made Heath-Robinsonish device which climbs up the curve of the central rib, and over the top of the lift bank; it has a cranked arm on the end of which is the cleaner's cradle. There is a similar gadget outside.

5 German office workers prefer individual cells, and these are normally provided by employers. This way of working does not seem to affect the economy's efficiency adversely.

6 The arches were delivered to the site in four sections, then welded together on the ground and hoisted vertical, with the hangers in place, restrained by temporary horizontal steel straps.

7 This layered facade gives a buffer zone of tempered air between the outer screen and the windows proper. The device is extremely popular in Germany these days, for it ensures that air drawn in through the openable windows is moderated in temperature, so balancing demands on air conditioning systems. Variants of the tactic are used in Plano's debis tower (p35 and AR January 1998) and Foster's Commerzbank (AR July 1997), and Ingenhoven's RWE hq (same issue).

Architect

Nicholas Grimshaw & Partners, London: Nicholas Grimshaw, Neven Sidor (design directors, London); Michael Pross (project director, Berlin); Ingrid Bille (associate in charge, London)

Design team (London)

Rowena Bate, Martin Bauer, Stefan Camenzind, Garry Colligan, Gavin Finnan, Kai Flender, Paul Grayshon, Andrew Hall, William Horgan, Ewan Jones, Matt Keeler, David Kirkland, Angelika Kovacic, John Lee, Benedict O'Looney, Stuart N. Piercy, Will Stevens, Dorothee Strauss

Design team (Berlin)

Andre Burmann, Thomas Deuble, Philip Engelbrecht, Raphael Forny, Birgit Greulich, Jens Hardvendel, Markus Hetzel, Carsten Kromschroder, Beate Muller, Susanne Raynor, Helle Schroder, Simon Wacker 

Structural engineers

Whitby & Bird; Specht Kalleja & Partners; Krupp Stahlbau Services engineer

RP+K Sozietat

Photographs

Werner Huthmacher 4, 6, 7, 8, 10, 11, 12, 13, 15, 17, 18

Jens Willebrand 1, 2, 3, 5, 9, 14, 16, 19, 20