Now you see it …

Pringle Richards Sharratt's winter garden is a brave attempt to reinvigorate Sheffield city centre. But with buildings growing around it faster than its own foliage, is it ever going to be fully appreciated?
By David Littlefield

Pringle Richards Sharratt is happy to concede that its winter garden is a 'hybrid' building. Smack in the middle of Sheffield, the beautiful construction of glulam and glass is not a botanical refuge in the manner of Paxton's Palm House or Grimshaw's Eden; neither is it a commercial centre, an entertainment complex or a destination building. This is a covered pathway, an elaborate pedestrian route linking one part of this slowly regenerating city to another.
The practice has been working in Sheffield since 1999, on the £13m Millennium Galleries that opened in April 2001 and the £5.28m winter garden. The projects function as a pair, with the galleries meeting the garden halfway along its south-eastern edge to form a colossal urban 'T' of internal arcades. At the moment, however, one end of the winter garden goes nowhere. The building stops short above a giant hole due to be filled in and turned into a public square by masterplanner Allies and Morrison. Unfortunately, by the time this is done, the garden will be overshadowed by a new hotel that will obliterate the only clear view of the structure's long elevation.

It is a shame that the full force of this eye-catching and graceful structure will be lost, because the visual weight of the building changes remarkably as one's viewpoint shifts. From either end, the sequence of rising inverted arches appears heavy and monumental; but as you walk around to the west, the winter garden reveals itself as a filigree structure of surprising transparency.

Partners John Pringle and Ian Sharratt try hard to be polite about the massing and height of Weintraub Associates' neighbouring hotel, but they must be privately appalled at the prospect of their building fading from view. The pair are volubly concerned about the garden's opening times of 8am to 6pm. These hours will greatly curtail what should be an uplifting journey through the city. As the centrepiece of a 2.5ha, £120m rebuild of Sheffield's cultural quarter, the garden should surely be open to those going out in the evening – Pringle and Sharratt conceived of it staying open until midnight. They describe the opening times as 'bloody ridiculous' and 'a disaster'.

It is also perhaps sad that the primary structure of the garden is German-made glulam, rather than good old-fashioned Sheffield steel. But symbolism aside, the choice is a good one: the use of timber represents a considerable cost and weight saving on steel and concrete alternatives and, anyway, weathering will eventually give the larch a steel-like patina.

These aesthetic and practical decisions (influenced by engineer Buro Happold, see box right) make the garden a very different place from the adjoining galleries. In fact, it is not obvious that they were designed as a pair – one is a concrete modulator of light, the other a glazed volume designed with the sole aim of sucking light in.

Sharratt is unapologetic about the two approaches, saying the programmes of each structure dictated different solutions – quite apart from the fact that galleries and gardens require contrasting climatic controls. This is fair enough, but the strategy leads to some discomfort where the two structures meet. It is worth remembering that much of the south-east wall of the garden was for 18 months the north-west facade of the gallery. This element still reads very much like an external wall that has been newly sheltered. It works, but it is neither seamless (as the practice claims), nor a celebration of contrasts in the manner of, say, Foster and Partners' Sackler Galleries.

Structurally, the garden is relatively simple. Nineteen pairs of arches march through the 75m site in steps of 7.5m (the same as the galleries). Half meet the ground by coming to rest on wonderfully executed steel cradles, while the others finish at gallery roof-height and sit on diagonal struts that help give the structure lateral stability. The stability is also enhanced by timber purlins that support the 1400 glazing units. A building management system controls opening roof panels, underfloor heating, fans and lighting to provide a temperature-controlled and frost-free environment for the temperate plants inside. The whole lot sits atop a concrete slab, providing car parking with vehicular access routes beneath.

Underneath the arches, some of the plants are very large beasts indeed (without careful management, the Norfolk Island Pine could easily outgrow the 22m highest point of the structure). But the architect has not forgotten that this is a city-centre space, not a new Eden. Instead of a labyrinth of paths that push through dense foliage, large expanses have been paved in local gritstone, and the plants and trees cluster into serpentine islands. It's more of a sculpture court than anything else. One can imagine this as a popular meeting place, as well as a convenient short-cut from, say, the Peace Gardens to the Crucible Theatre at the other end of Tudor Square. Pringle agrees: 'It's a place to dwell, rather than just move.'

Sheffield is a famously hilly city (The joke goes: 'Like Rome, Sheffield was built on a series of hills, and there the similarity ends') but the winter garden and the Millennium Galleries do a lot to even it out. More importantly, they are a brave attempt to reinvigorate the city through quality public spaces.

In a place that has had the life sucked out of it by the giant Meadowhall shopping complex, the council would have been forgiven for opting for a shopping mall. It is a risk worth taking, but one can only hope that market forces don't end up cramming this elegant and inspiring space with retail kiosks.

Specifications
Substructure by Hewletts, laminated timber structure by Merk Holzbau, roof glazing by Vitral, louvre glazing and doors by Glastec, structural bolted glazing by Haran Glass, lighting by iGuzzini, underfloor heating by Velta, stone flooring and cladding by Johnsons Wellfield Quarries, balustrading by Beely Fabrications, plants and water feature by Rentokil, roller blinds by Maple Sunscreening, signage by Widd Signs

How the winter garden grew up
The winter garden is 67.5m long and 22m wide, and rises at each end in a series of steps to 22m over the three central bays. The single-glazed building envelope and its 1400 framed roof panels are supported by a composite structure of laminated timber and stainless steel connectors in the form of primary larch arches and purlins. The larch glulams form an inverted catenary (the shape formed by a hanging chain) – an efficient shape that matches the force profile in the arch, thus reducing the size of the structural elements compared with traditional arch profiles.

Glulam was chosen rather than steel and concrete for various reasons – it can be curved to the required shape without the need for heavy plant (as required for bending steel); and an excellent surface finish can be obtained in timber by simply sanding the finished elements, unlike the problems with casting smooth concrete. Glulam also weighs only about 65% of the weight of a steel version and about 15% of a concrete alternative. Buro Happold

Credits
Client: Sheffield City Council 
Architect: Pringle Richards Sharratt Architects
Structural Engineer: Buro Happold
Services Engineer: Buro Happold
Project Manager: Sheffield Design & Property
Quantity Surveyor: Sheffield Design & Property
Planning supervisor: Sheffield Design & Property
Fire and access consultant: Buro Happold FEDRA
Lighting consultant: Bartenbach LichtLabor/Lichttechnik Martin Klingler
Winter garden landscape consultant: Weddle Landscape Design
Management contractor: Interserve Project Services

Link: RIBA Journal
© RIBA Journal 2003