A great deal to offer

Stephen Maddalena, Architectural Cladding Association, Leicester, UK

The retail sector in the UK is recognised as a vital contributor to the national economy with many millions of Britons visiting shopping centres each week. Currently, there is a development programme of over three million m2 in the pipeline, with many schemes exceeding 50,000m2, and the retail sector is looking to designers and builders to provide high-quality and innovative solutions to satisfy its requirements.

This is not simply a question of 'more of the same'. The tendency in recent years, both in towns and cities and in out-of-town sites, has been to create large, covered shopping centres where the car can be parked, leaving the public to concentrate on shopping.

Traditional street shopping

Although covered centres and malls are still being constructed, a new design, avoiding the need for roofs and incorporating open streets of shops, is increasingly being specified. Such streets are not open to vehicles and so very much resemble a pedestrianised town centre. Although some may consider this approach to be avant-garde, many in the construction industry are taking the move seriously and see it as the way forward. Whatever the viewpoint, large-scale, openstreet retail schemes are being planned in cities such as Cardiff, Bristol, Bath and Liverpool. These have taken their cue from redevelopments of Manchester's New Cathedral Street and Birmingham's Bullring, which have already acted as catalysts in the regeneration of their city centres.

These new regeneration schemes offer opportunities for the concrete industry, particularly with regard to precast cladding work. Instead of hundreds of identical facde elements fronting a massive covered out-of-town shopping centre, there will be a diversity of panel shapes and sizes in a myriad of finishes. In response to this, the building industry is increasingly adopting modern methods of construction to ensure that developers' expectations for optimum value are efficiently realised. This is where architectural precast cladding can be optimised as it has a great deal to offer.

Irrespective of whether the particular retail scheme is being developed in line with the current trend for an open streetscape, a covered shopping mall or a refurbishment of an existing centre, the direct and incidental benefits of precast cladding construction can be significant and particularly valuable, especially when considered and incorporated at a sufficiently early stage in its design.

Finishes and facings

The fact is that the choice of cladding finishes and facings is almost limitless. Reconstructed stone finishes that closely mimic the appearance of natural limestones and sandstones are often specified. Panels may also be faced with natural stone, granites, bricks and tiles. The inherent advantages of precast cladding construction are valuable and merit full consideration. As each precast cladding panel is cast off site in a purpose-built factory, it is inspected, held in store and available for delivery on a just-in-time basis for off-loading and hoisting directly to its final fixing position, thereby ensuring quality with efficient performance. This method of construction also eliminates the need for wasteful double handling of materials and temporary storage on site. The ability to provide a factory-finished product with preassembled stone, brick or tile facings avoids the common concern about the local availability of sufficient suitably qualified masons or brick layers to fit in with the programme. In addition, weather becomes far less critical to progress being achieved.

Large cladding panels, in particular, facilitate the rapid enclosure of all forms of structural frame and, where spanning between floor slabs or structural columns, avoid the need for secondary backing structure for their support and restraint. It may also be possible to design them to reduce mid-span loads in slab edge conditions. Moreover, concrete panels are fire resistant and provide effective sound control. Typically, a four- or five-person team of erectors can safely and efficiently install six to eight large precast cladding panels per day, generally without the need for an external scaffold. Access for the subsequent external pointing of the joints between them is then often provided by platform or cradle or even by abseiling. Further options include the opportunity for any window apertures within a precast cladding panel to be framed and glazed before despatch to site. A panel may also be supplied with insulation, either as a lining to its internal face or as a core between two concrete wythes, to enhance its thermal performance.

Case studies

Examples of reconstructed, stone-finished, precast cladding panels by Marble Mosaic Co include the 02 centre in London NW3, the St George Centre in Harrow (see Figure 1) and Churchill Square in Brighton. Facings options include natural stones, granites, bricks and tiles. The construction of ASDA's superstore in Bristol included brick-faced precast concrete arch units. Finishes and facings can even be mixed within a single cladding panel. The feature precast concrete buttress units at the West Quay shopping centre in Southampton incorporate knapped flint facings and a reconstructed stone 'Portland' finish,being part of a work package in excess of £4 million that was completed in 2000 and wall cladding panels with black granite facings and a reconstructed stone 'Portland' finish are currently being cast for Drake Circus in Plymouth.

Among recent projects carried out by Trent Concrete, following on from its work on The Mailbox and Martineau Place, Birmingham, and Manchester's Trafford Centre, are two prestigious retail centres - the Corner House, Nottingham, and the £500 million Bullring development in Birmingham, covering some lOha.

Corner House, Nottingham

Cladding features prominently on this retail and leisure development in Nottingham. The contract involved designing, manufacturing and erecting 3660m2 of reconstructed stone cladding. The 416 units include smooth-ground pilasters and acid etched window panels in a buff reconstructed stone mix. The Corner House is on the site of the former Nottingham Evening Post building and incorporates a 14-screen multiplex Warner Village cinema, bars, restaurants, shops and basement units.

Bullring, Birmingham

At Birmingham's Bullring development, Trent's contribution was 2500m2 of units faced with natural Italian Pietra Etrusca and Indian red sandstone, with complementary areas of matching reconstructed stone. The wide variety of units includes large flank wall panels, spandrels, mullions, column casings, cills, copings and window surrounds to all primary elevations. The project, opened at the end of 2003, includes department stores for Selfridges and Debenhams, together with more than 100 additional new shops, restaurants and cafes. Designed with traditional streets, walkways and public open spaces, the new Bullring is an integral part of Birmingham's city centre, connecting New Street and High Street with the markets, St Martins Church and Digbeth beyond.

Les Grands Pres, Mons, Belgium

Les Grands Pres shopping centre, completed earlier this year, has gained the Bureau International du Beton Manufacture (BIBM) Award 2005 for Outstanding Precast Concrete Projects for ACA member company Decomo NV, who supplied the architectural cladding. This project had to respond to a twofold architectural challenge: to create an image of quality in a semi-industrial building; and to create a strong and identifiable structural image, even though the building will ultimately have to blend into a planned residential area. These aims were met in three ways: first, by treating the facades of the shopping centre as a whole, using high-quality materials in a range of colours and paying great attention to detailing, lighting, etc.; second, by subdividing the main facades by means of pilaster and arch modules; and third, by adopting a large-scale approach to the centre entrances and the facade facing the public square. The facades are formed by a regular succession of arches and pilasters, 200mm proud of the main elevation and topped with lights. Four massive structures define the entrance. The east, south and west entrances consist of porches surmounted by triangular pediments, the massive frame columns being formed by alternating, two-toned architectural concrete modules. Beneath the arcades, the facade consists of architectural concrete elements for the shopping areas, with windows for the catering areas, around the edge of the public space and the west car park.

Dundrum, Dublin, Ireland

Ireland, too, is taking to architectural cladding. Dundrum, a village on the outskirts of Dublin, has recently been transformed into a major town centre with a 150,000m2 retail development - the largest in Ireland designed by Burke Kennedy Doyle Architects. As well as five major stores, there are to be 130 shops and 15 restaurants along with a theatre, exhibition and civic spaces. To reduce its impact and scale, the development was designed as a series of separate buildings. Facades are clad with a range of architectural precast panels from Techrete, using a blend of finishes including acid-etched, natural stone (granite and limestone) and terracotta tiles. The terracotta panels successfully reflect the local brick vernacular and were used for the first time in Ireland on this development. Their joints and corners are defined with aluminium channels and angles, creating crisp edges that match the precision of the stack-bonded terracotta tiles. The glazed main entrance to the shopping centre is flanked with precast panels faced with polished Giallo Bras Italian granite and articulated with horizontal bands of water-jetted granite. Two adjacent buildings are clad with precast panels faced with honed Jura limestone. Many of the precast panels are of insulated sandwich construction. The largest panels at Dundrum span 12m and weigh up to 13.5 tonnes. Slender panels up to 6.2m were also provided.

Conclusion

The great strength of precast concrete is that the choice, shape and size of panels are almost limitless; even complex shaped units can be provided with relative economy where repetitive. Whether the retail sector selects covered malls and out-of-town developments or opts for streetscapes, the architectural precast cladding industry can provide the solutions.