Kevin Jones, business manager of Aperam Stainless Steel Service UK Ltd, explains why stainless steel is a cost-effective building envelope material and how new surface finishes and coloured grades are widening its aesthetic appeal.
The increasing emphasis of design life value in commercial projects has prompted the development of metal facade and roofing systems of greater durability and lower maintenance. Despite its technical advantages, however, more widespread specification of stainless steel has been held back by the belief that it is expensive. Comparison of metal prices per tonne would certainly preclude selection in most situations but its enhanced strength means that thinner gauges are used, giving a completely different picture.
A typical minimum facade thickness for aluminium and copper is 1mm while that for zinc is 0.8mm and stainless steel just 0.5mm. Though roofing systems can be slightly thinner, a simple 300 sq m area requiring around 1 tonne of stainless steel will still weigh 1.5 tonnes or more in zinc or copper (and more than 10 tonnes in lead). In terms of large facade projects such as the new £45 million, 80,000 sq ft Marks and Spencer store on the Glasgow Fort retail development, 0.6mm stainless steel shingles specified by Cooper Cromar have saved up to 18 tonnes in facade weight. The design, described by the architects as ‘an elegant stainless steel-clad box’, has been designed to form a distinctive new entrance feature for the motorway frontage.
In total contrast, Wrap House (pictured) is a large 1960s family home in Godalming, Surrey, which Edgley Design was commissioned to ‘upcycle’. Their ultimate proposal extended and re-articulated its strong external forms using stainless steel cladding. Such finishes are among the most commonly associated with the metal and reflections on walls of the rural land- scape have brought colour and changing patterns to them throughout the day, creating a dynamic facade. This was achieved using a material with a relatively dull but uniform appearance combined with exceptional smoothness. It provides a shimmering envelope; in this case partly through use of an installation technique which creates visible waviness in flat areas of the standing seams and consequent abstraction of reflected forms. A standard mill surface was used but greater reflectivity could have been achieved by bright annealing and full mirror polishing.
The choice of visual effects which stainless steel can now provide includes linen, lozenge, leather and chequer patterns in a palette of different colours. Processes such as bead and sand blasting are used with rolling techniques which provide consis- tency of surface finish as well as lower cost. A roofing surface which takes on the patination of aged lead sheet has been approved by English Heritage as an alternative to lead where metal theft is considered a threat. A 0.5mm system weighing 4kg/m2 compares with zinc at 5.04kg and lead at 30kg or more. Introduction of a nickel-free ferritic grade has also done much to enhance price stability and competitiveness without com- promising performance. A material low in weight and as thin as 0.4mm can be used for standing seam, self-supporting and cleated seam systems.
The specification of compact, non-ventilated systems in warm roof build-ups has brought with it problems of underside corrosion with metals such as lead and zinc. Moisture trapped during installation or which passes through an inadequate vapour barrier provides the source for condensation to develop. Consequent failures are all the more costly as the problem invariably goes unnoticed until it is too late. Of the many reasons, therefore, why stainless steel is enjoying resurgence, its corrosion resistance in such situations is undoubtedly one of the most compelling. Once installed, stainless steel presents no risk to potable water, rainwater harvesting systems or water run-off, and will not stain masonry or timber. It is 100 per cent recyclable which means material can be re-used to manufacture roofing, facade, rainscreen or rainwater products rather than as a raw material for other industries. An exceptionally high melting point gives high fire resistance, while tensile strength is twice that of copper and more than four times that of aluminium. Surfaces offer the benefit of extremely low surface roughness and maximum resist- ance to the accumulation of contaminants. For over 100 years, the metal’s high performance has prompted use in the most demanding industries and environments. Outstanding corrosion resistance and design life is prompting its use in increasingly complex construction specifications and with demands for extended service life and low maintenance, stainless steel is surely set for a greater proportion of high profile projects.