IN TWO HALVES.

A dramatic and lively contribution to the city of Llubljana on one side encloses new concepts of semi-private space, and creates a new square. But the back is different.

In the middle of Ljubljana, the capital of Slovenia, is a big new building devoted to the burgeoning capitalist system of the young state. The Chamber of Economy is set back from Dimitz Street by a new square some 30m deep, a civic space which has been won by pushing the building back to the northern edge of the site as a slab. It is intended to be an economic 'megastore' stimulating flow of capital by providing consulting and educational services.

It makes a powerful (but not overpowering) impression on the piazza, for its south front moves in and out, with floors set askew to each other and eaten into, so sometimes the skin recedes to expose the skeleton, and at others, moves out to its normal enveloping condition. Arbitrary as this arrangement is, it is lively, and particularly at night, it clearly encloses tantalizing spaces. Voids, people, events, offices, libraries, lecture rooms and lobbies are all brilliantly displayed.

To understand what's going on, it's worth thinking of the structure. A series of long thin Vierendeel boxes are stacked one above another, all on slightly different axes. So far, the arbitrary angling is perhaps merely facadism, but the real interest of the design is in the way in which the rigidity of the Vierendeel frames is used to allow enclosed vertical space to flow up through the building from the entrance hall almost to the top, but moving east and west at each level. Architects Sadar in Vuga, who won the project in open competition, call the arrangement a vertical hall'. It creates a series of ledges, galleries, hovering places and transparent sided volumes, which provide a vast variety of views across, up, down, sideways and diagonally, a visual metaphor, it is hoped, of the multiple human interactions that will be generated in these semipublic spaces. The architects claim that the interior organization of the building 'responds to deterritorialization of capital' of the global economy, the 'pace o f expansion and exchange of information'. In fact, the result is rather the reverse: instead of deterritorialization, the strategy of the shifting vertical space creates many small particular, individual memorable places, quite the opposite of the dreary prescriptive spaces of most modern capitalism.

These are kept to the north side, which almost seems to be a different building. The structure changes from joggled steel to rational in-situ concrete, in which the main loads are taken in vertical circulation and duct shafts, with peripheral columns inside the north skin. An astonishing change this -- it is a bland, smooth, impersonal plane of curtain walling which might (with much good will) be compared to for instance Arne Jacobsen's taut, well proportioned 1950s glazing, but in a more gloomy, and perhaps more accurate perspective it becomes an almost scaleless slippery cliff.

Internally, the heavy north building is as dull as its skin, with cellular offices set along a long straight passage. But such spaces at least allow a degree of personal territory, and the internal interface between the stolid back and the fancy front provides much delight, as luminance and volume are revealed to the corridor.

This is very much a building of two halves, and it has many problems. But the firm is young, and much can be forgiven because of that vertical hall.