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 | | ZINC SUSTAINABILITY – STANDING THE TEST OF REAL EXAMINATION | | | VM Zinc (Umicore) Ltd | | 13/12/2007 | | | Sustainability is said to be one of the most misused terms in construction today, so definitive statistics from manufacturers rather than bland claims and hyperbole can only be welcome. It is surprising then that, among UK specifiers, there seems to be limited awareness of the fact that 30% of all zinc manufactured uses recycled material. Growth in its specification as a building product in the UK can be attributed to a number of factors, not least its lasting appearance and durability. In terms of re-use, however, the construction industry in Western Europe already recycles an exceptional level of the material, a point not wasted on architects seeking to combine aesthetics with true design life value. In fact, 90% of rolled zinc recovered from roofs and rainwater systems (around 100,000 tonnes each year) is now reclaimed. This owes much to a residual value which is as high as 60% to 75% of the new material cost.
Energy used to manufacture from ore is also the lowest of the non-ferrous metals - less than half that of copper, and a quarter that of aluminium. When using recycled material, energy consumption is even lower, with zinc still outperforming aluminium’s efficient manufacturing standards using reprocessed product.
Zinc’s use in urban environments declined post war as a consequence of smog and acid rain induced sulphur dioxide corrosion. Fossil fuel eradication in cities has now cured that problem to a point where the product’s design life typically exceeds 50 years. As an alternative to cast iron for guttering and lead for roofing it is also significantly lighter and less expensive. A 2-metre length of 125mm wide half-round cast iron gutter typically weighs 8.3kg compared to zinc at only 2.75 kg. But it is the added scope which zinc lends to contemporary designs which has been at the heart of its growing popularity. Use for rainwater goods is a fine example. Although still a relatively new concept in the UK, material and designs are filling a void between inexpensive but visually uninspiring PVCu and more traditional expensive cast iron. VM Zinc’s Pluline range is available in profiles to suit both residential and commercial use (even conservatories) and is manufactured using a patented pre-weathering process to produce either a quartz or an anthracite aged patination effect. Known as phosphatization, it occurs as a result of a slow change in the crystalline structure of both sides of the metal’s surface structure. The finish requires no surface treatment or painting and is resistant to surface marking during installation. Even in coastal environments, corrosion resistance is better than aluminium. Compared with cast iron too, it will not crack on impact.
For roofing, zinc is now favoured as an environmentally safe option to lead, particularly as its natural ageing process produces a similar patination. It is also easy to shape and form so that complex detailing can be undertaken in keeping with any style or age of structure. Architects have commented how well the material blends with wood, stone and concrete while providing a contrast with the plethora of glazing finishes available. 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.
A 62-section cupola 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 an intricate heritage design using zinc. Similar examples can be seen throughout Europe. By contrast, the curved roof structure used by Munkenbeck and Marshall for its design of a residential development in Kent is a striking example of a simple yet contemporary use of the material.
Maintaining an ecological equilibrium is essential for any naturally occurring material. Analysis of zinc concentrations in the Rhine, which passes through areas of the greatest industrial intensity, confirms that the balance is still well within acceptance tolerances. This has without doubt been aided by a dramatic reduction in zinc manufacturing’s industrial emissions (around 43% between 1983 and 1995 alone). The diversity of manufacturing uses for recycled zinc, including secondary refining, galvanizing, brass and zinc oxide production suggests that control of natural extraction will remain within manageable proportions. With levels of zinc recycling in the UK likely to be stimulated by the performance achieved in Europe, and an already buoyant market for reclaimed natural building materials in the UK, its use as a building product will doubtless soon develop at last to noticeable proportions. | |
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