Kew's alpine adventure

Architecture

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Now you see it ...

So delicate that it's almost invisible, the new Alpine House at Kew is a greenhouse for the 21st century, says Steve Rose

Monday March 6, 2006
The Guardian


Gimme shelter... Wilkinson Eyre's glasshouse is designed to let in as much light as possible while drawing in cool air to keep the plants from scorching

If there's one thing Britain loves more than pets, it's plants. We devour books and television programmes on them; we don't consider a house a home unless it's got a garden; and while we might have a few statues of eminent dogs scattered around the country, in Kew Gardens we have one of the world's most extravagant shrines to horticultural fanaticism.
The love affair shows no signs of waning: bucking the trend in the wake of the July 7 terrorist attacks, Kew's attendance was up 26% last year, to more than 1.5m visitors. But if you take away the plants (which is not encouraged), Kew is one of the most valuable architecture parks in the land, an unparalleled collection of fine and eccentric buildings reflecting 300-odd years of construction innovation and architectural fashion. The landscape has undergone a succession of contradictory redesigns, but the building stock prevails. From the 17th-century Kew Palace, where George III recuperated from his "madness", to the equally bonkers 10-storey pagoda; from the 1920s tea pavilion that was once burnt down by suffragettes, to the show-stealing Victorian glasshouses, Kew's buildings are a bizarre reflection of Britain as a whole.


And Kew's landscape is still evolving. Beyond the crocuses that will bring out the first wave of springtime pilgrims, there are major changes afoot this year. The entire 132-hectare site is being replanned, and some significant existing buildings are being reopened to the public, including the pagoda and Kew Palace, the latter after a 10-year restoration. There is also new construction, starting this week with a new Alpine House by Wilkinson Eyre Architects.
Wilkinson Eyre are also in charge of the Kew's long-term development plan, an initiative that sprang from Kew's registration as a Unesco World Heritage Site in 2003. The intention is to organise Kew's myriad layers of landscape design into a coherent, easily navigated whole. This will involve linking the site's peripheral features - from the main entrance to the east, along the Thames and round to the Temperate House at the western end - into a loose arc, bisected by the great Syon Vista, with the famous Palm House at its centre. New interventions are under construction along this route, including a characteristically elegant footbridge across the lake, designed by John Pawson.

The Alpine House was effectively a by-product of this process. The old, pyramid-shaped Alpine House never adequately fulfilled its function, and was in the way of an expansion of Kew's research building, the Jodrell Laboratory (also being carried out by Wilkinson Eyre). Noisy fans had to be installed to keep the air moving, the only shading was a layer of whitewash on the glass, and most of the alpine plants were actually grown in back-of-house nurseries, then transplanted to the glasshouse for public display. And, because of its out-of-the-way location, it was never much of a visitor attraction. "I didn't even know the old Alpine House existed," admits Wilkinson Eyre's Jim Eyre. "It was very obscure in its old location, so it was decided to put it in a prominent position and make something of the opportunity to do a 21st-century glasshouse."

Building a new glasshouse at Kew is a daunting proposition. Kew's Palm House is possibly the world's greatest surviving Victorian building, an awe-inspiring structure somewhere between a train station and a giant blancmange mould; it captures both the engineering brilliance and the exuberant vanity of its era. Its designers, Richard Turner and Decimus Burton, left other fine glass designs at Kew, including the even larger Temperate House; further back, there's William Chambers' 18th-century neoclassical Orangery, which was once claimed to be England's biggest glasshouse. More recent additions have been less remarkable: the 1950s Evolution House looks like a glorified garden-centre greenhouse. The interior of the 1987 Princess of Wales Conservatory, with its steamy rooms of orchids and ferns, has been more of a success, but compared to subsequent leaps made elsewhere, such as Nicholas Grimshaw's Eden Project or Norman Foster's giant glasshouse at the imperilled National Botanic Gardens of Wales, Kew's legacy started to look a little dated.

Despite its modest scale, the new Alpine House certainly brings things up to date. It is situated next door to the Princess of Wales Conservatory, in the rock garden and, although it rises to almost the same height, it is minuscule in comparison. In contrast to its neighbour's Toblerone chunkiness, the Alpine House is lightness itself, both in terms of its structure and its transparency. Its simple, curving shell harks back to the romanticism of the original Palm House, but, unlike the Victorian examples, this building seems to be all glass and hardly any steel. From certain angles, it is practically invisible.

Visual considerations were purely secondary, says Eyre, although he does acknowledge that the arched structure resembles a double version of Wilkinson Eyre's famous "winking" bridge in Gateshead. The form of the building was dictated purely by the needs of Kew's Alpine plants, which include well-known varieties of saxifrages, peonies, gentians and rosemary, and more exotic oddities such as cushion plants, which can be killed simply by touching them. "A glasshouse for Alpine conditions is almost the exact opposite of a glasshouse for anything else," Eyre explains. "Generally speaking with glasshouses, you're trying to keep plants warm and shelter them from the general nastiness of our weather. Here, we want to keep them dry but we want to keep them cool. They have to have lots of light and they need to be well ventilated. There wasn't any brief about what it had to look like, but we agreed to use passive ventilation, which is not what most people have done in the past."

Recreating Matterhorn-like conditions in Surrey is a challenge at the best of times; try and do it through only natural means and you've got a mountain to climb. But, despite its apparent simplicity, this little building overcomes its contradictory requirements ingeniously. The height is essential. As the air inside the Alpine House heats up and rises, it is drawn out through openings at the top, on the inside, faces of the central spine. This in turn draws in cool air through the vents at the bottom of the building. To get the air moving even more (without air movement, the plants tend to grow "leggy", according to a Kew representative), the concrete base of the glasshouse acts as a heat sink. A small fan draws air through a maze of concrete passages beneath the floor, and a series of vents directs the cooled air up and across the plants above.

To achieve the light levels required without compromising this system, the building is north-south oriented, so as to present a narrow profile to the sun. The curvature of the east and west sides also helps to deflect direct sunlight. However, the panes of glass are flat, not curved, so that the sun is only directly concentrated on a single facet of the cladding at any time of day. The glazing is supported on slender, precisely tuned cables running between the four arches like the strings of a harp. In conjunction with special low-iron-content glass, the building's structure achieves a transparency of nearly 90%, allowing for the high light levels the plants require. And when it gets too hot, there are giant mechanical shades that fan out across the sides of the building like a peacock's tail.

The fact that the Alpine House requires so little external power qualifies it as a genuine 21st-century advance in glasshouse design. This building would not have been possible without current technology, particularly the detailed computer simulations provided by environmental engineers, Atelier 10, and the fact that it looks the part is an inevitable consequence. In the months to come, Kew's grander attractions will doubtless be stealing the limelight. The prospect of nosing around the restored Kew Palace will doubtless draw even more visitors to Kew, but, in its unassuming way, the Alpine House is a fitting project to kick off Kew's year of change.