The Princess of Wales Conservatory, 1989

The Princess of Wales Conservatory, 1989

by Mateo Rossi Rolando 1979 - 1988

Propert Services AgencyGordon Wilson, Project ArchitectA Sarkar, Lead Civil Engineer

The Bartlett School of ArchitectureEngineering & Architectural Design MEng: History and Theory Essay, Year 1

The Bartlett School of ArchitectureEngineering & Architectural Design MEng: History and Theory, Year 1

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An illustrated Essay of the Princess of Wales Conservatory at the Royal Botanical Gardens, Kew, London

Mateo Rossi Rolando

Figure 2: Titan Arum flower at the Princess of Wales Conservatory

An Illustrated Essay of the Princess of Wales Conservatory at the Royal Botanical Gardens, Kew, London

It would be an understatement to call the task of de-signing a new icon for Kew Gardens difficult. Regardless, the feat was achieved in the 80s by the Property Ser-vices Agency with their Princess of Wales Conservatory. This essay explores how and why this greenhouse has earned its place on the podium beside the Palm House and Temperate House, considering first its physical and relative situation, then explain the ideas and theories of engineering crucial in the building’s design. Subsequent-ly, analyse the spatial arrangement and interior design that uniquely define the experience of the Princess of Wales Conservatory. Then, briefly look at the cost, and penultimately, review the critical reception. Concluding with a personal statement explicating the focal points to answer the question.

Introduction

The role of a glasshouse, or to use the more archaic but appropriate term, ‘forcing house’, is to provide, artificially, a climate for plants to grow outside of their native envi-ronments. As such when engaging in a qualitative assess-ment of a glasshouse it is salient to review its engineering, for the ultimate and defining test is whether the floral inhabitants are thriving and flourishing. ‘In 1989, [The Princess of Wales Conservatory] became the first place to experience the flowering of the Titan Arum outside of its native Sumatra’1, the largest flowering structure in the world, a testament to the conservatories potential.

Commissioned in 1982, completed in 1985, and unveiled

to the public by Princess Diana of Wales in 1987. Albeit having Diana’s title, the Conservatory was named after the Princess Augusta of Wales (b.1719 – d.1772), one of the founders of the Botanical Gardens in Kew. Its princi-pal Architect and Project Manager was Gordon Wilson, the lead civil engineer was A Sarkar both of which were working for the Property Services Agency2.

Prior to this build, Kew Gardens was already home to two iconic glasshouses, the Palm House designed by Decimus Burton and Richard Turner, and the Temperate House designed also by Decimus Burton. Both glass-houses are emblems of the Botanical gardens of Kew and their architectural period. The Temperate House and Palm House are on similar sites, the land beneath them is slightly raised working as pedestals for the magnificent sculptures of glass and metal. They were intended to be the icons they’ve become. Burton and Turner were archi-tects at the frontier of an era of unprecedented innova-tion. The Princess of Wales Conservatory is different, it


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has not been commissioned as a show piece and scruti-nising it against its neighbours seems unfair. It’s a building of a different time, asking for different and specific things. All of which, complicate the design until there is a form created from its functions.

Brief and site of the building

The client’s (Royal Botanical Gardens, Kew) brief was to replace 263 glasshouses that had come to the end of their economic life. Additional and necessary requirements were4: that the building had to last over a hundred years. Contain ten climatic zones under one roof, which had to be computer controlled and be technically advanced in its methods of energy consumption and climate regu-lation. The superstructure’s maintenance had to be low cost, safe and easily accessible. The Wales Conservatory was to become the largest at Kew by area, 4490 sqm5. It was to be home only to herbaceous plants which grow to approximately 7 or 8 meters - not requiring as tall a roof as the Palm House and Temperate House. The Sher-man Hoyt collection of cacti had to be placed within the glasshouse. As well as Cacti, various other succulents, Orchids, Ferns, Carnivorous and Tropical Plants6 had to be accommodated. Blending the building into the sur-rounding topology while still being a sculptural object was also important.

The site is large, and abnormally shaped, resulting in the building plan being kite shaped orientated on the long axis towards north. There are north and south entrances for visitors and a maintenance entrance located in its north east section. Typically, a glasshouse will have the maintenance area in the north7, but the visitors entrance required it to be placed elsewhere.

Figure 3: satelleite image of the Princess of Wales Conservatory and its position in Kew.

Figure 4: Building plan and the climatic zones.


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Efficient technology

In 1991 the Princess of Wales conservatory was award-ed the Engineering Heritage Hallmark for being opened as the ‘worlds most advanced energy efficient conserva-tory’8, it had already won at least ten more awards in the years prior. The ten climates are regulated by computers, in its inception it was done so by the leading technology9. The necessary conditions - temperature, humidity, and more – are monitored in each zone. This information is then relayed to the computers and they will automati-cally decide if and how the zones condition should be altered. Considering the exponential advancement of computers this dialog improves and becomes less ob-trusive every year, availability of technology is no longer an issue.

The excellence of this conservatory lies in its thought-ful design of the fundamental. Wilsons concept for the design was influenced in his visits to the greenhouses of North America and Europe pre-commissioning of the project in 198210. Put descriptively, the shape is a scattered set of thin triangular prisms. The shape has a low ratio of volume to surface area11; therefore, internal conditions can be changed faster and consequently use less energy. At a latitude of 50˚, the North facing part of a building receives no direct sunlight. The roof and concrete floor rise northwards, with two purposes: to allow the plants to have the most direct sunlight yearly and to minimise interplant light obstruction. At its peak the hill structure suddenly steps down again, only the winter climatic zone is placed in this most northern part of the building.

The zones that require the highest temperatures and humidity are adjacent to each other and in the centre; above the in situ concrete boiler room. In this manner

the heat that they radiate attempts to be conserved through dissipating it to other zones before being lost to the outside.

Ventilation is achieved with mechanised openings of glass panels connected to every ridge; wind sensors are on the roof that override this mechanism and shut the panels if winds are too strong. Wind loads could not be

Figure 6: Sketchup model of ‘triangular prisms’ with solstice sun paths and altitude lines. Summer altitude line 59o. Winter altitude line 15o.

N

Figure 5: Award plaques in the conservatory


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Figure 8: Superstructure of rising prisms

Figure 7: Diagram showing some of the working technologies in the green-house.

calculated from the BS standards12, so computer models, and wind tunnel testing on a prototype, were used to determine these loads. These were lower than expected due to the various ridges in the structure inhibiting the development of vortices on the roof13.

Additional heating comes from below the pathways and at the perimeter with various convectors. There are Pun-ka fans14 that recirculate the air to avoid layers of stag-nant air forming. Humidity is controlled with mist sprays attached to the valley purlins. All the sensors are imper-manent and can be replaced as the technology improves, such sensors can be found in each zone contained with-in white Chinese lantern shaped capsules. Three water tanks dispersed around the site, only one is within the structure’s boundaries. Up to 275,000 litres of rain wa-ter can be collected off the roofs and stored in the tanks, these are deep enough underground to prevent the wa-ter freezing. A water reserve with a potential of lasting 15 days15.

The Superstructure

The glass roof structure compromises of large pitched panels of glazing that extend to the ground, varying in height and width at points by adding extra pitches. The massive roof pitches to the east and west, with its ver-tical walls facing north, and south. Rough cut glass was used for the roofing to suppress the view of the external structure from an insider’s perspective, also to frame the thin leaved plants that may have been lost against the clear sky16, and to evenly disperse the incoming sunlight by the dimples in the glass. The vertical walls are clear glass to ‘prevent any feelings of claustrophobia’17 which is so crucial to the buildings success, it shows oneself


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where they are in the building and provides a visual con-nection to outside.

The roof cascades from a maximum height of 11.4m from the tropical ferns zone. The ground mimics the shape of the roof, this reduces light obstruction from plants that may be further south. The pitch of the sloping roof is 26.5o. An angle that partially reflects a high suns light18, this, as well as the vertical glazing fulfilling the same pur-pose, will act to reduce overheating in the summer.

The supporting structure is entirely low carbon steel. Use of stainless steel was deemed too expensive, and al-uminium would have required impermissibly deep foun-dations. The steel used is 43E grade (BS 4360: 1979)19, apart from the hollow Vierendeel tubes. Wilson wanted to reduce their size for aesthetic reasons, accordingly, a stronger 50D grade steel was selected to compensate. The glazing bar and overlap seal are bespoke aluminium extrusions20. The lap seal tackles the important problem of condensation plant damage by draining it out through ‘weep holes’. Where the structural columns are in plant-ing beds the steel is cast over with concrete, as such the climbing plants have been able to grow and make use the space available.

Spatial and Interior Design

Wilsons glasshouse is not only a forcing house. It is im-mersive. Very rarely do you see through to either end. As the paths wind through each climate you can lose yourself in the roofed jungle. Going through the building only once, you will, assuredly, neglect one of the zones. New levels are continuously introduced to move up and down to. Thus, the views are manifold, where entire sec-

tions can be seen from various heights - an element that is surprising and refreshingly new when considering the usual plan of flat orthogonal paths, as there are in most of Kew’s greenhouses.

Figure 9: Thin leaves against rough cut glass

Figure 10: Bay from the exterior


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New floor levels had to be set, and excavation of the site was required, the ground level surrounding the su-perstructure had to be raised and lowered to hide the walls, each bay hugging the ground, sinking the structure into its surroundings. Internal Volumes have been deter-mined by the scales of plants and their respective loca-tion in the plan. The smaller carnivorous plants are in the littlest zone of all and the structure focuses one’s gaze onto them. In comparison, in the tropical ferns zone, the highest zone, one climbs up the stairs into a massive ex-pansive space, with large clear glass windows on either side, and intuitively you look up to the tallest plants in the greenhouse.

Externally the steel frame is unavoidable, but from within, the translucency of the rough-cut glazing blurs out and away the visually heavy and distracting structure. Vieren-deel tubes were implemented behind the roof purlins to not add any more unnecessary distracting lines21 behind the view of the plants.

Comparing the three largest greenhouse’s path widths, the path in the Princess of Wales is the narrowest. The temperate house is the second largest in area of the greenhouses, but a vast part of this is reserved as public space. In the Princess of Wales Conservatory, the op-posite is true, furthermore, measures have been taken to allow some encroachment of the plants into the pe-destrian space. All plants on the longest side of the Palm House are in raised beds with a rounded finish or are at waist level with a ledge and column detail. Again, the opposite is seen in the Princess of Wales Conservatory, the finishes are much simpler. The plant beds are not raised from the path, but level with it. An angular cut is employed thoroughly, from the waist high viewing beds in brick, to the limestone aggregate bench, this continui-

ty makes the simple feature an excellent detail. Further-more, the simplicity of detail and the importance placed on plant space, are illustrative of the greenhouse Wilson intended.

Cost

Gordon Wilson applied a “structural span philosophy” where large span structures escalate in cost in geometric proportion to the span. – the largest span in the building

Figures 11&12: Diagrams demonstrating views varying with levels. Fig 11 also shows plants receiving unob-strocted light because of this step.


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9Figure xx: An external view of the National Theatre

was only 14m. In total the cost was £5million for 4490 sqm roughly a £1000/sqm22, a price two or three times less than greenhouses being built at the time in North America and Europe.

Critical reception

The conservatory was in majority well received. Winning multiple awards. The Architects Journal 1986 June mag-azine featured a critical review on the greenhouse by Michael Stacey, which was in turn said to have been dis-

approved of by the President of the RIBA. This is under-standable, Stacey’s criticism was almost entirely focused on the various glazings and aluminium extrusions that the PSA misused, as such he avoided key and defining el-ements of the Conservatory, missing the point. Inevitably his expertise in these topics is what led him to harp on these details. His suggestion for cross bracing to replace the Vierendeel tubes in each bay - idealising a ‘high tech’ solution - is uninformed and shows the perniciousness in his line of criticisms. Whether the building “breaks less new ground”23 is questionable and perhaps an insensitive comment to make.

Conclusions

When designing a public greenhouse, there exists the question, ‘who is this place for?’. Here, I believe, Wilson made no compromises in trying to make an excellent space for both. The wealth of nature and how it’s been offered is precious, this is a model for minimally inva-sive greenhouses, and I wouldn’t be surprising if the Eden Project had taken notes.

This building is an exemplar of engineering and archi-tecture. The engineering required optimally to grow the plants has induced an architecture that is completely immersive, that topologically emulates the native land-scapes, and has over the decades nurtured the beautiful display that is there today.

While the Palm House and Temperate House stand out, this complex machine, nestled between the trees, hum-bly sits, waiting to impress.

Figure 13: Bench with cut corner

Figure 14: Finishings on the planting beds in the Palm House


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Fig 1: Leo Kauntz Moderini

Fig 2: http://powo.science.kew.org/taxon/urn:lsid:ip-ni.org:names:84456-1

http://www.beenthere-donethat.org.uk/london/lon-don-kew011big.html

Fig 3: Google Maps Satellite Image

Fig 4, 8: An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Bo-tanical Gardens Kew: planning and design || ICE virtual library

Fig 5, 9, 10, 13: My own photograph

Fig 6: My own Printscreen

Fig 7, 11, 12: My own Drawing

Fig 14: http://www.beenthere-donethat.org.uk/london/london-kew011big.html

Image Credits


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An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library

Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory

John Hix, the Glass House

BS 4360 is now obsolete, and I would have had to pay a large sum to find this specification for graded steels; so here is the specification that contains 43 and 50 grade steels, EN 10025:2004 http://rfl.ie/specs/

Engineering Heritage Awards Handbook ImechE page 59

http://www.spartaengineering.com/vortex-shedding-and-tall-structures/

http://www.beenthere-donethat.org.uk/london/lon-don-kew011big.html image Palm House

http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:84456-1

Https://www.kew.org/training-and-courses/horticul-tural-training/kew-modular-certificate-glasshouse-dis-play-practices-princess

Bibliography


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Endnotes1 Https://www.kew.org/training-and-courses/horticultural-training/kew-modular-certificate-glass-house-display-practices-princess 2 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library 3 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey4 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library

5 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey

6 Https://www.kew.org/training-and-courses/horticultural-training/kew-modular-certificate-glass-house-display-practices-princess7 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library

8 Engineering Heritage Awards Handbook ImechE page 599 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library

10 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey11 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library12 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory13 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal


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Botanical Gardens Kew: planning and design || ICE virtual library

14 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory15 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library

16 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory17 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory18 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey19 An Engineers guide to an award-winning project The Princess of Wales Conservatory at the Royal Botanical Gardens Kew: planning and design || ICE virtual library20 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey21 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory

22 Princess of Wales Conservatory Tour Architectural tour notes by Gordon Wilson, architect of the conservatory23 1986 May Architects Journal – Construction Studies – 4 Glass Conservatory at Kew – Michael Stacey

The Princess of Wales Conservatory, 1989

Documents

Transcript of The Princess of Wales Conservatory, 1989