Unite and rule

Endeavour House is set about a spacious light-filled concourse that doubles as an art gallery, and manages an exhilarating civic presence. As well as giving councillors a compact debating chamber it serves Suffolk's long suffering population by bringing together for the first time staff from 1000 different departments. And as a bonus, councillors can show off their commitment to renewable energy with what is billed as the largest integral installation of photovoltaic cells in Europe.

Yet the amazing thing about the new building, considering the fact that council members and their officials look so much at home in it, is that it wasn't designed or built for the council at all. The original client was TXU, an American-owned gas and electricity distributor, but it went into administration in November 2002, 15 weeks before contract was due to finish. The administrator set up a fire sale of the company's assets, and the county council picked up the unfinished building at a snip in April 2003 – along with the project team of architect TTSP and contractor Bovis Lend Lease. Twelve months later, it moved into the building, which had been completed as originally designed, except for the neat addition of a 90-seat council chamber and a fit-out to suit council staff.

In its configuration, Endeavour House is essentially inward-looking, as the site offers little scope for Urban Design. Bounded by the town's large, craggy football stadium on one side and a collection of nondescript industrial buildings on the other, the site is more like a business park than the traditional county-hall setting at the heart of a historic county town.

TTSP's response to the rectangular site was to configure the building as two office slabs running parallel to the road and separated by an atrium. As the site is oblong, the atrium is effectively a long concourse. And as the office slab in front has been kept relatively short, the central concourse has been allowed to burst out at either end into great halls like large greenhouses entirely enclosed behind transparent, frameless window walls.

One of these large quasi-greenhouses is the main entrance hall. It is lofty, spacious, and awash with daylight – so much so, in fact, that the reception desk has had to be tucked away from the glare within a passageway at the back. At present, it is also plain, featureless and commands views of little more than the football club car park. But to one side, it leads through card-operated turnstiles and below a narrow footbridge into the central concourse.

Coming straight after the vapid entrance hall, the concourse is an unexpectedly dynamic affair. Four storeys high and generously proportioned, it buzzes with architectural and social activity. Overhead, footbridges fly across at crazy angles like something out of Blade Runner and wide, open-tread, steel staircases cantilever out into the open space. Open-access balconies line the concourse on either side, and these sporadically widen into informal break-out spaces.

Although long and deep, the concourse feels anything but cavernous. Daylight floods in through a flat-glazed roof and bounces off the polished, creamy-white limestone floor. Sunlight plays over the whole assembly, casting shadows of the delicate, steel roof structure, thereby adding another shifting layer of dynamic patterning. At ground level, exhibitions of local paintings line the whitewashed walls.

A further layer of activity is provided by council staff, who constantly traverse all the footbridges, balconies and stairs on everyday business, and small clusters of staff coalesce next to the drinks dispensers in the break-out spaces to hold impromptu meetings.

At the far end of the concourse, another even brighter and more social spectacle draws the visitor through. It unfolds as a large, relaxed, apparently open-air restaurant furnished in plywood ant chairs in a variety of fresh pastel colours and shaded on one side by mature cedar and pine trees.

This, the staff restaurant, is actually enclosed within the second large quasi-greenhouse, although several devices combine to create the open-air effect. First of all, the clear frameless glazing descends to the limestone floor, which runs without interruption through to external terraces below the trees on two sides. Second, the restaurant occupies an airy, light-filled, double-height space, with only a cafe perched on a delicate gallery between the floor and the ceiling two floors up. Finally, pools of water and gurgling curtains of vertical water shoots combine to further enliven the scene.

The actual office space is contained on either side of the concourse in relatively narrow, 17 m deep floorplates. There are no cellular offices – even department heads share the general open-plan space. There are, however, plenty of small meeting rooms enclosed behind glazed partitions.

The council has branded the building its "strategic decision-making home". The act of centralising administration has had a dramatic effect on council organisation and production. As Peter Revell, the council's project manager, explains, "it has broken down departmental silos that existed in separate buildings before, when it was the case that ne'er the twain shall meet".

More to the point, the headquarters has enabled the council to establish closer co-operation between departments. This addresses the need for council's to improve their internal communication governmental demands that followed the tragic death of Victoria Climbié. With insufficient time to organise comprehensive restructuring, the council opted instead to bring together teams from different departments that were working on common causes. And it is not just the open-plan office floors that generates staff interaction. The break-out areas with their drinks dispensers and generous circulation balconies, footbridges and stairs all encourage staff to spread around the building and meet each other.

"Here, each floor is based on a theme," explains Revell. "One floor is themed around children, young people and families, and this brings together teams from the social care and education departments. Another floor is themed around community safety and brings together teams dealing with trading standards, youth offending and racial harassment. Not long after we moved in, a guy from trading standards found himself standing at the coffee machine next to someone from youth offending. After a casual chat, he discovered they were both working on under-age sales, but from different standpoints. So the building design improves the service to the public."

The council debating chamber, which is the only substantial council-initiated change to the basic shell and core, fits neatly into the office building. It takes pride of place at the far end of the concourse on the second floor directly above the restaurant. A wintergarden had originally been planned for this spot, but fortunately it had still to be constructed when the TXU went into administration.

The chamber takes the form of a compact oval enclosure containing 90 desks for councillors and a narrow press and viewing gallery on one side. As Seoras Burnett, associate at TTSP, explains: "We first planned it in the round. But councillors said they wanted a traditional, confrontational situation between parties, so we changed it to an oval." With its compact layout, undulating acoustic baffles of glass-reinforced concrete and plain grey carpets, it is an efficient, if not exactly impressive, space. It was built without needing to reinforce the existing supporting structure, and with the only physical alteration being to demolish part of a curtain wall to allow access to councillors' office space.

Externally, the building still looks more like a smart corporate headquarters than a centre of regional government. The main view from the street is of a modest-sized, neatly detailed office block sandwiched between two large greenhouses at either end. The quasi-greenhouse around the restaurant is the most attractive part, as views of its spacious, light-filled restaurant with its chic collection of coloured chairs emerge through a ring of mature trees.

The curtain wall to the offices breaks a significant energy record: it is claimed to incorporate the largest integral installation of photovoltaic cells in Europe. The arrays are physically integrated into the fabric of the building rather than being bolt-ons. More precisely, they are incorporated into the double-glazed spandrel panels of the curtain wall, where they add a satisfying, dark patterning effect to the flat facade and allow some daylight to filter through to the office interiors. In full sunlight, the 50,000 cells should supply more than 57% of peak electricity demand of the building, which is otherwise conventionally air-conditioned.

Endeavour House is a fine example of a building that is both an attractive and efficient workplace. And the fact that it was originally designed and built for quite a different organisation fulfills another principle of good design – it is flexible enough to accommodate inevitable change.