Zinc for Diversity

An average of 20% growth per annum since 2005 in public sector non-residential construction reflects the level of investment in health and education over the period. However, while most types of metal roofing, facades and rainscreen cladding have experienced a similar rate of increase, zinc has certainly outstripped it.

Growth in zinc’s specification as a building product can be attributed to a number of factors, not least its lasting appearance, low maintenance, design life cost and durability. It combines well with other materials, particularly timber and a wide range of glazing styles. In terms of specific elements of design, warm roof construction in commercial projects once required use of bulky ventilation inlets and outlets, causing loss of internal roof height, extended build time and additional cost.

Contact with the atmosphere provides the CO2 without which the metal’s ongoing natural patination cannot develop. If condensation occurs for any reason, corrosion will result. The introduction, therefore, of zinc coated to obviate the need for underside ventilation has been a significant development.

Various alternatives are available to achieve classes of internal humidity load up to 5. These include zinc on cellular glass, mineral wool and PIR, as well as composite panels. The composite panel approach, using Foamglas also enables zinc to be used in environments such as swimming pools, in which chemicals would otherwise cause damage as they evaporate.

Zinc makes a major contribution to thermal efficiency, in keeping with successive changes to Part L of the Building Regulations in England and Wales.Philip Proctor Associates’ design of Sandroyd Pre-Prep School in Salisbury used VM Zinc Plus on Foamglas, for a 650m2 standing seam application over profiled acoustic decking. The lightly curved two tier roof construction is a major element of the low scale of the building and was designed to create a gentle atmosphere.

Its suitability for pitches as low as 3°, in addition to straight, curved and folded shapes means it can be used to accommodate virtually any design style. Ruddle Wilkinson’s design for Hampton Hargate Primary School in Peterborough utilised zinc standing seam roofing to achieve a series of contemporary, low pitch roofs. The specification used zinc hips, verge detailing, guttering and cladding, the facades adding a design edge by linking single and two storey roofs.

An extension to Tiffin School in Kingston on Thames illustrates another low pitch construction, but a total design contrast. The modern circular roof provided a new focal point for the school, but complements an established, traditional Georgian brick and slate frontage.

Zinc is ideal for larger roof spans, while its malleability lends it to intricate detailing. Diversity of appearance can be achieved through surfaces which include pre-weathered patination, now routinely supplied in preference to natural zinc. Less well known is that a number of colours are also available. The chapel at Mosley Hall Hospital in Birmingham shows how simple detailing can achieve a distinctive, but suitably unobtrusive finish. This particular project used concealed gutters but as an alternative to plastic and cast iron guttering, conventional zinc rainwater goods offer a far longer deign life than plastic, a modern style using concealed brackets and no ongoing need for recoating. A 2-metre length of 125mm wide half-round cast iron guttering also weighs around 8.3kg compared to zinc at only 2.75 kg.

Unlike other metals, zinc retains its appearance without additional protection and therefore costs far less in respect of long-term maintenance. In terms of sustainability, the degree to which old rolled zinc is being recycled is high. As much as 90% is reclaimed in mainland Europe (around 100,000 tonnes each year), and if the UK still has some way to go to match such standards, there is clearly a determination to use building materials which minimize environmental impact. Energy used to manufacture zinc from its ore is the lowest of the non-ferrous metals – less than half that of copper, and a quarter that of aluminium. Even when comparing manufacturing performance using recycled materials, energy consumption is over 30% lower than that used for aluminium. At 150N/mm2, tensile strength is high, while a melting point of 420°C provides resistance to surface spread of flame to Class 0 / Class 1.

With the additional benefit of BRE certification (VM Zinc -BRE137/07) for interlocking facade panels the scope for cladding, roofing and drainage projects using zinc is greater than ever before. Its long term cost, low maintenance and colour retention are major distinguishable benefits against other metals. With a typical design life exceeding 50 years and the virtual guarantee that material will be fully recycled when refurbishment is necessary, there is clear evidence that the metal combines sustainability with durability.

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