As well as wide applications in contemporary architectural design, there is more to copper than meets the eye when it comes to recyclability, sustainability and longevity, explains Graeme Bell of Aurubis
Copper is a natural element found within the earth’s crust, and which has been incorporated into living organisms throughout evolution. The wide range of architectural copper surfaces and products available today replicate natural ‘mineralogical’ changes that otherwise occur over time in response to the local environment. They are produced in modern plants with strictly monitored environmental performance, and well-established recycling routes. The solutions available to architects include high levels of recycled materials, saving on energy and greenhouse gases, and contributing to the circular economy.
While offering a lightweight and flexible covering for building facades, copper can also reduce structural support demands, resulting in lower carbon and ‘whole of life’ costs. Then, at the end of a building’s life, the material retains a high scrap value which drives recovery and recycling. Copper can be recycled again and again without any loss of performance or qualities, and its lifespan can be regarded conservatively as 200 years when correctly installed. When copper roofs or facades are replaced, it is generally due to substrate or structure failure, rather than the copper.
Copper requires no decoration, maintenance or cleaning – saving resources, cleaning chemicals and cost. Its interaction with the environment has been assessed under the European REACH policy on chemicals, and has no classification or restrictions under that process.
Architectural & practical
The material’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 even repair itself if damaged, which accounts for the material’s longevity. A complex combination of factors determines the nature and speed of development of patina over time and this is much slower on vertical surfaces. It is not surprising that factory-applied surface treatments are popular to provide ‘straightaway’ oxidisation and patination of copper to a required level, particularly for facades.
Having an A1 (non-combustible material) fire classification to EN 13501-1, copper is suitable for cladding tall buildings, using appropriate constructions of course. Low thermal movement makes it safe and straightforward to use in any climates and locations. Also particularly important today, copper is non-toxic and its inherent antimicrobial qualities make it ideal for touch surfaces, including interiors.
Many of the processes involved with copper are very similar to those already taking place in the environment. Copper mineral compounds, rather than chemical interventions, bring forward 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). Ongoing changes will continue over time, depending on the local environment, defining copper’s ‘living character.’
These surface treatments include pre-oxidised copper, where the thickness of the oxide layer determines the colour lightness or darkness. Alternatively, pre-patination utilises the same ‘brochantite’ mineralogy found in natural patinas all over the world. In marine climates, the natural copper patina contains some copper chloride giving it a blue-green colour, and this is emulated using 100% brochantite mineral. Alternatively, using a hint of iron sulphate yellow replicates greener natural patinas. With pre-patination, the process can be accurately controlled so that, as well as the solid patina colours, other intensities of patina flecks can be created revealing some of the dark oxidised background material to give a ‘living’ surface.
Copper alloys have been used throughout history, with bronze and brass – which can also be pre-weathered – remaining popular for architectural applications. Innovative copper alloy gives a rich golden through-colour which is retained without developing a blue/green patina. It simply loses some of its sheen as the oxide layer thickens with exposure to the atmosphere, creating a protective matt finish.
Apart from traditionally jointed, rolled material supported by a substrate, various other forms of copper are increasingly being explored by designers. For example, copper can be supplied in profiled sheets or extremely flat honeycomb panels, pressed to provide surface textures and modulation, or perforated, expanded or woven as mesh, enabling transparency.
Graeme Bell is Nordic Copper sales and marketing manager at the Building, Construction and Architectural division of Aurubis