Maintenance & Refurbishment
Architectural copper for the long term
There is more to architectural copper than meets the eye, with an unrivalled lifespan counted in hundreds of years, no maintenance and full recyclability as Graeme Bell of Aurubis explains
D
espite its heritage, roofing some of our oldest buildings, continuing developments make copper and its alloys thoroughly modern and sustainable cladding materials for today’s urban housing.
Copper’s longevity is due to a complex patination process. It ensures extreme
durability with no maintenance and resistance to corrosion in virtually any atmospheric conditions. And, unlike some other architectural metals, copper does not suffer from underside corrosion. The empirical evidence of copper’s longevity cannot be matched by more recently developed cladding materials. The rate of reduction of a copper roof surface decreases with patination and equates to no more than 5 per cent reduction over 100 years.
WHOLE LIFE BENEFITS The lifespan of copper roofing and cladding can therefore be regarded conservatively as 200 years, subject to substrate and structure – and this is endorsed by experience. Naturally, this longevity has a significant effect upon comparative whole of life assessments. With copper, it is invariably the supporting substrate or structure which eventually fails, rather than the copper cladding itself. Therefore, the selection of appropriate substrate and build-up are essential. In addition, copper requires no maintenance or decoration. As a lightweight and flexible covering, structural support demands are reduced, resulting in lower carbon and ‘whole of life’ costs. Copper is also fully recyclable utilising long-established practices – 97 per cent of copper in construction comes from recycling – and has other impressive sustainability and environmental credentials. And, of course, copper retains a high scrap value at demolition.
SAFE MATERIAL With a melting point of 1083˚C and ‘A1 (non-combustible material)’ fire classification to EN 13501-1, copper is also suitable for cladding tall buildings, using appropriate constructions. Low thermal movement makes it appropriate for any climate and location, and it is non-toxic and safe to handle, as well as non-brittle and safe to work. Its inherent antimicrobial qualities make it ideal for touch surfaces internally as well. Copper’s unique architectural qualities are defined by its naturally
developing patina – which cannot be replicated successfully using other materials with surface coatings. Within a few days of exposure to the atmosphere, a copper surface begins to oxidise, changing from the ‘bright’ mill finish to a chestnut brown, which gradually darkens over several years to a chocolate brown. Continued weathering can eventually result in the distinctive green or blue patina seen on older roofs. The patina film provides impressive protection against corrosion and can
repair itself if damaged, giving its exceptional longevity. A complex combination of factors determines the nature and speed of development of patina over the years. So, it is not surprising that factory-applied surface treatments are popular to provide straightaway oxidisation and patination of copper surfaces to a selected level, particularly for facades.
NATURAL PROCESSES Some of the processes involved are very similar to those taking place in the environment and utilise copper mineral compounds, not alien chemical actions.
38 | HMM April/May 2019 |
www.housingmmonline.co.uk
Cladding & External Finishes Feature
Essentially, they bring forward the environmental changes without taking away the integrity of copper as a natural, living material. They form an integral part of the copper and are not coatings or paint, and on-going changes will continue over time depending on the local environment. These surface treatments include pre-oxidised copper, where the
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