It may look like a Bond villain's lair, but the gleaming glasshouse nestling in the Welsh hills is Foster and Partners' centrepiece to the £43.3m botanic garden.
Like the villain in a James Bond film, Foster and Partners has a fondness for developments that are both outlandishly futuristic and at the same time nearly hidden in their setting.

This skill has been deployed in the curving glass Willis Faber building in Ipswich, which self-effacingly mirrors the surrounding buildings, and in the terminal at Stansted Airport, which nestles so low in the Essex countryside that it is invisible until you are on the approach driveway.

An even bigger surprise awaits as you drive through the lush Carmarthenshire countryside towards the new National Botanic Garden of Wales. The country lane gets narrower, more winding and more overgrown. Then, as you pass over the crest of one more hillock, you suddenly glimpse another that is blatantly artificial. It is of the same size and gently rounded shape as its grassy neighbours, if slightly lower. But there is no disguising its synthetic composition, as the clear glass panels that cover it gleam brightly in the sunshine. One can just imagine the glass roof silently parting in the middle to reveal a row of deadly intercontinental ballistic missiles.

In reality, the glass hillock contains nothing more sinister than a collection of Mediterranean plants. It is a conservatory, and a huge one at that. Measuring 95 × 55 m on plan, it is the largest single-span conservatory in existence and will contain 10 000 plants collected from Mediterranean climatic regions across the world.

The interior of the great glasshouse is currently being landscaped by Gustafson Porter, the London practice set up by radical landscape architect Kathryn Gustafson of Seattle, winner of the international competition to re-landscape Crystal Palace Park in south London. This is Gustafson’s first built project in Britain: she was appointed after the botanic garden’s directors found British entries to their design competition too tame.

The glass dome and its contents are the centrepiece of the newly created botanic garden, which stretches across 230 ha of countryside, surrounded by another 136 ha of model organic farms. Before construction started in 1997, there was nothing on the site but a derelict 18th-century estate.

The venture was the idea of a local painter, William Wilkins, but has now been granted the standing of a national institution by the Welsh Office and is run by Professor Charles Stirton, formerly deputy director of the Royal Botanical Gardens, Kew. The garden cost £45m, of which £8.9m was absorbed by the dome and its landscaping; it received a Millennium Commission grant of £21.7m. It is due to open to the public next Easter.

Proclaimed as “a new concept in botanic gardens”, the National Botanic Garden of Wales is based on a vision of “a world where we understand, value, use, enjoy and sustain plant life to create a balance of life on earth”. Made of glass, steel and concrete, Foster’s great glasshouse may not be the most environment-friendly building in construction terms, but its rounded form certainly fits snugly into Carmarthenshire’s arcadian countryside.

“The brilliance of Foster’s design is how the building has been moulded into the ancient landscape of Carmarthenshire,” enthuses the garden’s head of marketing, Gary Davies. “Especially since we live in a part of the world where builders are not allowed to use anything other than Welsh slate.”

The interior of the dome is as much a surprise as its exterior. In contrast to the elliptical steel arches overhead, Gustafson Porter’s landscape has neither curving forms nor flowing lines. Instead of conventional mounds of earth, a jagged ravine some 6 m deep has been cut through the floor of the conservatory and lined with sheer sandstone walls.

Rather than trying to mimic nature, the man-made nature of the installation has been emphasised by the use of dressed stone, and the entire ground surface has been covered with a rough scree of crushed sandstone.

The ravine has been carefully angled to create areas of sunlight and shade, and waterfalls that will provide suitable habitats for a wide range of Mediterranean plants. The silvery-coloured sandstone is imported from Germany; even on a cloudy day, the effect is literally dazzling.

As for Foster’s enclosing dome, it is a simple building suited to the straightforward function of protecting this little offshore island of Mediterranean nature from the British weather. It is nothing more than a shallow, elliptical dome set at a slight angle of 7º to the horizontal, facing south towards the sun.

Designed by structural engineer Ove Arup & Partners, the glass dome is supported on a parallel series of steel cross arches that all share the same radius of curvature and cross-section.

The arches rise out of the elliptical rim in fairface concrete, which tilts up on the north face to accommodate a couple of narrow demonstration rooms and toilets, with staff and plant rooms in the basement below. The elements of the building have been distilled to their essence so that their combined effect is beautifully simple, elegant and without frills, which is only to be expected from Foster. The one special feature of the whole assembly is the exposed bearings at either end of the steel arches, many of which are within reach of visitors. These bearings take the form of ball-and-socket joints made of superbly finished, polished stainless steel.

The simplicity of design makes the dome appear deceptively small. It is only when you look across the landscaped floor of the glasshouse that you realise it is the size of a football pitch.

In sunlight, the arches create striking bands of shadow across the floor of the glasshouse.

Months before its full opening, the great glasshouse has been adopted as the venue for a series of garden design programmes to be broadcast on television in autumn. Although perhaps with less suspense than James Bond films, these programmes exploit the spectacle and glamour of Foster’s futuristic glasshouse and of Gustafson Porter’s dramatic landscaping inside.

What else is at the botanic garden?

  • The £45m National Botanic Garden of Wales will open next Easter as “a new concept in botanic gardens” across 230 ha of the rural Tywi Valley of Carmarthenshire. A 136 ha outer belt will be run as a demonstration project for organic farming.
  • The garden’s centrepiece is the £8.9m glasshouse designed by Foster and Partners, which contains 10 000 plants from Mediterranean regions.
  • Other completed buildings include a circular gatehouse, also designed by Foster, and a £200 000 water discovery centre designed by the Welsh School of Architecture.
  • The botanic garden is intended to be largely self-sustaining. A district heating system is fired by a biomass boiler that burns tree thinnings and willow coppicing from the estate. A string of lakes will be used to irrigate plants. Sewage will be treated by a compact “living machine” anaerobic digester before being returned to the land.
  • Later phases will include visitor facilities, to be converted out of an 18th-century stable block, and a £5m science centre.

Why Foster and Partners is forever designing bubbles

“You can have any building form you want, as long as it’s a torus.” It may be blasphemous to compare Foster and Partners’ design approach with Henry Ford’s crude mass production techniques. Even so, the elliptical bubble-shaped form of the torus has become the architect’s hallmark.
  • The torus form has been used by the practice in the vaulted concrete roof of Duxford Air Museum, the glazed entrance canopies to underground stations in Bilbao and London’s Canary Wharf, and the riverfront facade to the proposed Greater London Authority headquarters. For the £8.9m glasshouse at the new National Botanic Garden of Wales, a torus shape has been adopted for the entire glazed dome, which is all that is visible of the building externally.
  • A torus has a longitudinal radius much larger than the cross radius. This means that if the curved surfaces of the Welsh glasshouse were extended in all directions, it would form an enormous doughnut almost entirely submerged underground.
  • The double-curving bubble shape of a torus is as satisfying as an old-fashioned dome. It can also be squashed or elongated, made shallower or deeper or tilted at various angles. At the Welsh botanic garden, a shallow torus form 12 m high has been designed on an oval base of 95 × 55 m, which is tilted at 7° to the horizontal.
  • “The biggest challenge [of the entire dome project] was posed by the complexities of the 3D modelling, and achieving the quality required by the design consultants,” says Derek Foster of construction manager Schal. Detailed design was only feasible using leading-edge computer-aided design.
  • Some 1000 flat laminated glass panels, each 18 mm thick and about 4 × 1.5 m in area, were fitted to the double-curved profile of the dome by cutting the edges to make trapezoidal shapes. A total of 500 different trapezoidal shapes of glass were manufactured by Akelt of Austria.
  • The structural frame took the comparatively simple form of a series of 24 parallel steel cross arches of identical curvature and section. Each arch is made up of a 323 mm diameter steel tube with a steel T-section welded to its upper surface. Steel purlins in the longitudinal axis provide stiffening.
  • The glazing bars were supplied and fixed to the top flanges of the T-beams by Metallbau Früh of Austria.
  • A unique ball-and-socket joint was designed to form a pin joint at either end of each arch. Design engineer Wolf Mangelsdorf of Ove Arup & Partners says: “The pin joint operates on the principle of a human hip joint, as it has the possibility to rotate in any direction.” With this degree of flexibility, a standard joint could be used to support all the arches, which meet the base of the dome at widely different angles on both vertical and horizontal axes.
  • The ball-and-socket joints were made of spun stainless steel by Watson Steel and bolted at right angles to a steel plate fixed to an insitu concrete ring beam.
  • The tilted base of the dome was cast in insitu concrete to match the torus’ geometry. Concrete subcontractor Byrne Brothers appointed a specialist surveying consultant to transfer co-ordinates from the CAD model to locations on site.
  • The dome interior is heated to 5° above external temperatures by the sun and thermostatically controlled perimeter radiators. Ventilation is provided by 148 opening glazed rooflights and low-level fans that create Mediterranean wind effects.