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
Despite 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.
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.
Some of the processes involved are very similar to those taking place in the environment and utilise copper mineral compounds, not alien chemical actions. 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 thickness of the oxide layer determines the colour lightness or darkness. Then, pre-patination enables designers to determine both the colour and intensity of blue/green pfatina for each project with ‘living’ surfaces. Here, as well as a solid patina colour, other intensities can be created revealing some of the dark oxidised background material.
Of course, copper alloys have also been used throughout history and bronze and brass – which can also be pre-weathered – remain popular for architectural applications. In addition, a recently developed alloy of copper with aluminium and zinc gives a rich golden through-colour. Its surface retains the golden through-colour and simply loses some of its sheen, as the oxide layer thickens with exposure to the atmosphere to give a protective matt finish. This golden alloy behaves differently to other copper products over time and does not develop a blue/green patina.
Graeme Bell is Nordic Copper sales & marketing manager at Aurubis
The new Ram Quarter mixed-use development at the heart of the London Borough of Wandsworth is highlighted by its rooftop cladding of green pre-patinated copper, reflecting the site’s industrial heritage. It also demonstrates the capabilities of copper cladding for urban housing. The site was formerly home to the Young’s brewery and its regeneration has encompassed the restoration of historic buildings alongside the construction of stunning new-build apartments. The three phases of Ram Quarter will deliver 713 homes, nearly 100,000 sq ft of shops and community and leisure facilities over 8 acres. Greenland Group UK, the developer of Ram Quarter, was keen that the site’s material specification should help to reflect the history of the site and deliver high-quality design and long-term durability. EPR Architects, the appointed architectural practice for the scheme, commented: “The oldest fermenting and brewing vessels within the old brewery were copper. This inspired us to predominantly clad the upper two floors of the tallest residential buildings in Nordic Green Living 1 copper. Adjacent to the historic brewery complex we introduced a playful vertical expression to one of the new buildings – a nod to the industrial vats – raised from the ground with softer rounded corners and vertically-ribbed profiled copper cladding.”