Out to Graz - botanical gardens

Architectural Review, The, Oct, 1995 by Peter Blundell Jones

In the university's new botanical glasshouses, Volker Giencke displays the love of exploring route, light and aperspective space that characterises much of the work of the Graz architects.

Volker Giencke is perhaps the most wide-ranging and unpredictable architect of the Graz movement. His early connections with the Scharoun circle and his great respect for the master nurtured in him a strong interest in route, light and aperspective space as well as a readiness to experiment with complex-building forms.(1) Later, he worked for Gunther Domenig as job architect on the curious shell-like dining hall inserted into the courtyard of a convent at Graz-Eggenberg, one of that architect's most 'organic' works (AR May 1981, p293).

But at the same time, Giencke has continuously demonstrated a strong tectonic interest. He is always concerned about the way the substance of the building contributes to its atmosphere, and he likes to show how it goes together, so the structure is often on display and the layering of elements is made explicit, while innovation in detail - for example the flush glazing in his timber houses (AR December 1988, p86, April 1990, p43) - can play a decisive role. From the beginning, his apparently wilder and more irregular works, such as the glasshouses considered here and the Aigen church (AR April 1992, p70), were balanced by cooler orthogonal designs such as the Karl Spitzweg Strasse housing (p63). And the fact that Giencke has recently chosen to build his own house within a rectangular steel frame shows that this more restrained approach is no less close to his heart than the other. But when his designs are examined in detail, apparent differences evaporate somewhat: there is always a firm rationale whatever the form.

The new glasshouses are set in the Botanical Gardens of Graz in the university quarter on the west side of the city. They were originally designed in 1983, but due to bureaucratic and financial delays they were only completed this year.(2) The programme required a series of publicly visitable greenhouses offering strong daylight but different climatic conditions, and a nursery for breeding plants. Giencke's intention was to make the most efficient contemporary glasshouse using the latest technology, a modern equivalent of the palmhouse at Kew. After careful consideration of precedents,(3) the idea of a linear building of parabolic section was adopted. This linearity - as opposed to a circular glasshouse like the Glasgow Kibble limits the span and makes the building narrow enough to allow all plants good access to light, but also makes the glasshouse directional. The parabolic section, being tall in the middle, allows space for trees to grow without creating excessive volume or surface area, and sets the flank walls perpendicular to the low morning and evening winter sun. Such a linear building is best placed on the north-south axis to receive the sun throughout its daily path. Tilting the form along its axis towards the south increases the sunlight transmission in the middle of the day besides dramatising the building's relationship with the earth. Hence the placing of the largest and most important of the glasshouses north-south across the corner of the Botanical Gardens skewed about 35 degrees from the street grid, This contains the temperate house at its north end, the succulent house (cacti) to the south, while the circulation hub of the whole complex occupies the middle.

The combination in one volume of the temperate and succulent houses left a requirement for two further glasshouses which Giencke treated as variations on the theme. In both cases ideal orientation was abandoned in favour of relating to the site. The cold house flanks the north-eastern site boundary, helping to create a front for the building. Here the parabolic section is cut back to create a much steeper facade against the street, and is protected from the busy path along the front by a moat-like pool. The tropical house, a further variation on the parabolic theme, projects to the south-west.

All four glasshouses share the same technology and control systems. The parabolic arch structure is built in aluminium for lightness and avoidance of corrosion, though steel cables are added as ties against wind load. It is double glazed on the outside with curved acrylic sheets, achieving a light transmission of around 98 per cent, the highest so far achieved internationally. Since the structural sections are hollow, hot water can be pumped around them so they act as heating radiators. Cooling is effected first by ventilation involving input of air at ground level and exhaust through vents at the apex, and second - in the cold house particularly - by periodic spraying from pipes at high level of a fine mist of water droplets. This humidifies the air as well as dropping the temperature instantaneously by five degrees.

The general plan arrangement allows the four houses with their different climates to converge on a central crossroads for visitors, for the route was also an important consideration in the design. It traverses several levels involving a variety of stairs and bridge-like ramps, creating its own forms which play against the major volumes, sometimes running outside them with separate tent-like envelopes. The organisation is simple despite the complexity of form. Each of the four glasshouses has its own Iooping path allowing views from a variety of levels. Starting on or even below ground, the paths swing up on to suspended bridge-like ramps and return via the central paired staircases, giving a different experience each time. The aim is clearly a promenade architecturale which also allows one to see the plants from a variety of viewpoints. The external ramp on the back which plunges into the building playing against its main volumes is reminiscent of Le Corbusier's Carpenter Center, but a closer if less obvious precedent in terms of both form and organisation is Scharoun's Gerd Rosen Gallery project of 1948 with its central double staircase and outer loops, each contrived to take you up to the main gallery floor in a different way.