Richard Rogers has once again turned convention on its head in its radical design of Antwerp's law courts building, opened this week by the King of Belgium.

Sitting in one of six large courtrooms in Antwerp's new law courts you would be forgiven for thinking you were in a church. Overhead, four curving shells of warm natural timber arch steeply heavenwards to a sharp apex, while below a diamond-shaped latticework of projecting beams seems to change subtly in angle as it criss-crosses upwards from a wide base. Between the shell, strips of clear glazing allow natural daylight to flood in and the courtrooms are bounded on three sides by continuous clear-glazed windows with low sills. So, if the case threatens to drone on, you can refresh your mind by glancing out at the changing weather, down to the great glazed hall below or beyond to the cityscape or parkland spread out on either side.

But wait. Isn't this the most archetypally straitjacketed and security-ridden of building types, a state courthouse? How do you explain the sculptural rooftop eruption rather than a position safely embedded in the bowels of the building?

The simple explanation is that the building is an international competition-winning design by Richard Rogers Partnership of London, and exhibits all the practice's much-vaunted devotion to clear glazing, daylight and transparency. And, just as in the Welsh Assembly building, these attributes come with a lofty democratic ideal - "making the working of justice more transparent".

The result is downright revolutionary. No other courtrooms have windows at seat level, claims the practice, not even the Bordeaux courthouse it completed in 1998.

In each large courtroom, a curving timber roof soars overhead and large, clear-glazed windows offer views at seat level

In each large courtroom, a curving timber roof soars overhead and large, clear-glazed windows offer views at seat level

Crediot: Grant Smith

In an arrangement that turns the traditional courthouse on its head, six large courtrooms have been fitted on to the top, fifth floor of the huge building, with 28 smaller courts strung out along six narrow wings up to 240 m long that radiate from either side of the core. At its heart is a large and lofty public hall that rises up through the three top storeys. Most of the four lower floors are given over to lawyers' offices, plant rooms and other ancillary spaces. The public has to find their way up from ground level, but the payoff is unrestricted light and exhilarating vistas across the city rooftops.

Narrow fingers of green parkland penetrate between the wings to the core of the building. In another departure from the usual compacted city-centre site, the courthouse had the good fortune to be located at the eastern edge of the city where an old railway station had been demolished and the site adopted by residents as a rough-and-ready park.

The public hall is a column-free space enclosed by glass roof and walls. Leading to all six wings on either side, it works and feels like a big-city railway terminus. Unrestricted views lead down the tree-lined boulevard beyond the front entrance, across the new park at the rear and to the river docks on one side. Adding drama, the two central courtrooms cantilever into the hall above smooth concrete bellies on either side. Less inspiring is the glass roof itself, with heavy tubular steel beams and overcomplicated geometry created by the six wings connections.

The 26 courtrooms in the six wings are topped by lower, more modest timber shells but are shut off from external views by corridors running along either side of each wing. One is used by judges and the other the public, so the groups don't meet. Defendants for criminal trials arrive directly by lift from secure remand cells in the basement.

The lower floors of the 18 m wide wings are mostly occupied by lawyers' offices and meeting rooms arranged as conventional cellular offices along either side of a central corridor. A restaurant and social spaces are located below the main public hall.

Viewed from the outside, the courthouse gives no indication of the warm, curving, timber interiors. From the centre of Antwerp, there are glimpses of what looks like an extraordinary flotilla of sails. But on approach one finds not billowing fabric, but sharp, steel-clad spires or spikes that border on the sinister - like beaks, fangs, or even, dare one say it, Ku Klux Klan hoods.

The spacious public hall on the third floor is aligned with the city’s main boulevard, which ducks directly below the building

The spacious public hall on the third floor is aligned with the city’s main boulevard, which ducks directly below the building

Credit: Grant Smith

According to Ivan Harbour, Roger's senior director running the project, the spires were a response to the Antwerp cityscape. "Antwerp is essentially five or six storeys in height with church spires poking out," he says. "Although the building is enormous, we wanted to work with the city scale, whereas all the other competition entries were 20 to 30 storey towers."

The country's rather bleak landscape affected the design as well. "For the competition entry we had the spires facing both ways and arranged symmetrically around the central hall," he says. "But Belgium is very flat, and as I was riding down a country lane I noticed that all the trees are slanting in the direction of the prevailing wind. They were planted by man but formed by nature. So we did the same with the spires - they now all face in the same direction."

Beneath the spikes, the building is repetitive, disciplined and functional, more like an aircraft carrier than a schooner. The dominant material is glass, either as clear-glazed window walls on the top floor or fritted louvres fronting the floors below. As a final flourish, the glazed top floor breaks into a triple-height section near its midpoint across the public hall. A huge external staircase leads up to it from a spacious public square in front of the building.

The square shape, the long glass facades and the grand external staircase are all reminiscent of Roger's first public building, the Pompidou Centre in Paris. They give a suitably civic, monumental character, albeit in a functional modern vocabulary. The spikes on parade along the rooftops are like public art objects writ large.

In this way, the building stands as an imposing stop-end to the city's main boulevard running eastwards. In reality, it performs a more dramatic role as gateway because the boulevard dives into tunnel below the building and reappears on the other side as the open motorway to Bruges and Ghent. Traffic has been reduced in the orbital road by a new tramline, and this measure along with generous planting has restored the large space in front of the building to what it once was - a lively and amenable civic square.

The sculptural rooftop spires are visible from Antwerp’s city centre

The sculptural rooftop spires are visible from Antwerp’s city centre

Credit: Katsuhisa Kida

All in all, Richard Rogers Partnership has come up with yet another landmark building. Although less rich and engaging than the Bordeaux courthouse, it yanks this venerable building type decidedly into the 21st century while still retaining its traditional monumental and civic attributes.

All the trees are slanting in the direction of the prevailing wind. So we did the same with the spires – they now all face in the same direction

Antwerp law courts key points

  • Conventional courthouse layout turned on its head by placing public spaces on top floor to gain
    views and daylight through windows and skylights
  • Prominent sculptural roofscape created by quadruple hyberbolic parabaloid roofs over courtrooms
  • By straddling truck road on city perimeter, building serves as gateway to Antwerp

Cool for courts: The low-energy ventilation strategy

Low-energy use was central to the architectural concept, but considerations of comfort limited Rogers’ ambitions. “We extended the roofs upwards to catch the prevailing winds and create a natural stack effect internally,” says Ivan Harbour, Rogers’ senior director. “So we were disappointed the natural ventilation wasn’t carried through.”

Andrew McDowell, Arup’s environmental engineer, explains why not. “The client wanted to be absolutely sure of comfort conditions in the courtrooms and to avoid security and noise problems of openings. So we introduced mechanical displacement ventilation and ran a stainless steel extract duct down from the apex of the roof.”

The courtrooms gain daylight from north-facing clerestory windows between the upper and lower pairs of hyperbolic parabaloid shells. In the office floors below, opening windows provide natural ventilation and summertime cooling. Treated fresh air is supplied through a central duct below the raised floor and extracted through an exposed high level duct. It also purges excess heat at night.

The underside of the precast concrete roof planks are exposed to act as a heat sink and troughed to increase their surface area. External glass louvres reduce solar gain.

The energy performance in the offices is anticipated at 70% of UK good practice cellular naturally ventilated offices, as defined by DETR ECON 19.

How Rogers & Co designed the roof

“We spent a couple of years playing around with shapes,” says Ivan Harbour, director at Rogers. “And then an obvious solution came up and we jumped on it. That was to divide each roof into four separate parabaloids. This meant we could add glazing for daylight between the shells and also prefabricate them in modules that were small enough to manoeuvre easily.” A hyperbolic parabaloid is basically a rectangular plane with opposite corners bent forwards and backwards. The beauty of the form is that the shells are richly curved and structurally rigid yet can be made up of simple straight beams and purlins. Each shell was made of a grid of timber beams and boarding set within a tubular steel frame.The lower floors are supported on repetitive system of precast concrete frames. The columns and perimeter beams run along either side of each wing, with prestressed troughed planks spanning clear between them. This arrangement provides flexible column-free interiors.

Twisted logic: Constructing the spiky curves

In theory, curving hyperbolic parabaloid gridshells are ingeniously simple structures that can be made out of a grid of straight beams. In practice, however, awkward wedge-shaped gaps occur between flat beams and the curving shell surface they support. Unless, that is, the beams are allowed to twist slightly.

For the courtroom roofs, the dilemma was solved by specialist timber subcontractor Finnforest Merck. Instead of the making the beams as single chunky lengths of wood, it built them up in a rig
by criss-crossing thin planks on top of each other in alternating directions and glueing and screwing them together. The novel system was dubbed “screwlam”.

The timber shells were bolted to tubular steel frames with the curving surface applied as half-lapped timber boarding.

Prefabrication took place in a huge shipbuilding shed a few miles upstream from the site. The completed shells were lifted by the shipyard’s giant gantry crane and transported to site by barge and wide-load truck. Four shells making up one complete courtroom roof was delivered and lifted into final position each week.

The shells were then covered with 0.4 mm thick stainless steel sheeting fixed with welded steel upstands.

Project team

Client Regie der Gebouwen
Architects Richard Rogers Partnership, Bureau Van Kerckhove 
Structural and services engineers Arup, Bureau Van Kerckhove
Facade engineer Lesos

Quantity surveyor Bureau Van Kerckhove
Landscape architect Wirtz International
Main contractors Interbuild, KBC, Dexia