Growth in specification of zinc as a building product in the UK owes much to its lasting appearance, malleability and corrosion resistance. It blends well with wood, stone and concrete and provides a contrast with the plethora of glazing finishes available.
As a roof covering it can be formed into the most complex shapes and used at pitches as low as 3°C. Though less well known for standing seam systems than aluminium, zinc is now receiving widespread public attention as a consequence of projects featured in, for example, the 2007 Grand Designs Awards.
Bere Architects' Focus House in Finsbury Park won Best Eco-House and used VM Zinc Plus® in a quartz-zinc finish with a concealed zinc rainwater system for the warm roof construction. The patented pre-weathering process produces a patinated appearance and texture which resembles aged material. The finish requires no surface treatment or painting and is resistant to surface marking during installation.
Osborne Homes' demonstration house built recently at the BRE, was designed as an entry in the £60,000 house competition to demonstrate low cost, affordable, sustainable construction incorporating the latest thinking in waste reduction and energy efficiency. Zinc was used for roofing, guttering and cladding in a structure that was built in a day and a half. By complete contrast, for his design of Quarry House in Sevenoaks, architect Steve Marshall of Munkenbeck and Marshall specified a combination of larch for the structural timber and zinc for the dramatic curved roof. The silver-grey larch will blend with the zinc's gradual patination.
Like the timber, specified from an FSC accredited source, the zinc was chosen for its sustainability. 30% of all zinc manufactured now uses recycled material while in western Europe, 90% of rolled zinc recovered from roofs and rainwater systems (around 100,000t each year) is now reclaimed. There is already evidence of the knock-on effect in the UK; for the restoration of Brighton railway station the original zinc supplied by VM Zinc a century ago was removed, recycled and new material from the same manufacturer applied. Recycling may owe much to the trend towards care of natural resources, but a high residual value of 60% to 75% of the current new material cost is, undeniably, playing a large part.
Energy used to manufacture, whether from ore or reclaimed material, is the lowest of the non-ferrous metals - less than half that of copper, and a quarter that of aluminium. Even against the cost of manufacturing using recycled aluminium, zinc's energy consumption is around a third lower.
New technology affecting zinc manufacture now enables production of materials in a variety of finishes and colours. In addition to Quartz-zinc, Anthra-zinc, a deeper charcoal colour, is produced for more contemporary architectural styling, while blue, red and green in the newly launched Pigmento range take the naturally grained texture of pre-weathered Quartz-zinc a stage further.
Zinc’s use in urban environments began to increase once risk of smog and acid rain-induced sulphur dioxide corrosion began to reduce following fossil fuel eradication. This now means that the product’s quoted design life invariably exceeds 50 years.
As an alternative to cast iron it is also significantly lighter and less expensive - a 2m length of 125mm wide half-round zinc gutter weighs only 2.75kg compared to cast iron at over 8kg. Although still relatively new as a guttering material in the UK, it is beginning to fill a void between inexpensive but visually uninspiring PVCu and more traditional but expensive cast iron. Even in coastal environments, corrosion resistance is higher than that of aluminium and unlike cast iron it has no susceptibility to impact cracking. At 150N/mm², tensile strength is high too, while a melting point of 420°C provides resistance to surface spread of flame to Class 0/Class 1.
As an environmentally safe option to lead, zinc is now finding use too on heritage projects and even contemporary designs of the few churches now being built. A 62-section cupola zinc roof, specified by Dannatt Johnson for the recently refurbished mid 19th century Clapham bandstand thought to be the biggest of its type remaining in the UK, is a good example of a intricate involving intricate detail.
Maintaining an ecological equilibrium is essential for any naturally occurring material. Analysis of zinc concentrations in the Rhine confirms that the balance is still well within acceptance tolerances. Emissions resulting from zinc manufacturing continue to reduce (down 43% between 1983 and 1995), while the diversity of uses for reclaimed product, including galvanizing, zinc oxide and brass production, suggests that natural extraction will remain within manageable proportions. With zinc use in the UK likely to be stimulated by the growing market for reclaimed and natural building materials, its future looks healthy in every respect.