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cladding & facades 29 Copper kerb appeal

Copper producer Aurubis discusses the wide variety of copper surfaces available for cladding today and how they can be used in conjunction with other materials to add architectural quality to housing

and characteristics. We have witnessed its trans- formation from an historic role as a durable roofing material to a flexible architectural skin over any surfaces, notably facades. Its growth in popularity amongst architects has been signifi- cant and it is often used extensively throughout facades as the predominant material, effectively defining the architecture of high quality build- ings of all types. But it can also be applied more sparingly in


housing projects to complement other, perhaps lower-cost, materials, adding kerb appeal. Here, it can act as a highlight, perhaps defining entrances and vertical circulation areas, where the material will continue to develop its natural appearance over time adding distinctive character to developments.

Impressive protection

The natural development of a blue or green patina is one of copper’s unique characteristics. Within a few days of exposure to the atmosphere, the surface begins to oxidise, changing its colour from the ‘bright’ mill finish to a chestnut brown, which gradually darkens over several years to a

opper was one of the first metals used by man and is one of our oldest build- ing materials, with unique properties

chocolate brown. Continued weathering can eventually result in the distinctive green or blue patina seen on older roofs. The patina film pro- vides impressive protection against corrosion and can repair itself if damaged, defining the excep- tional longevity of copper cladding and roofing.

“The material will continue to develop its natural appearance over time adding distinctive character to developments”

A complex combination of factors determines

the nature and speed of development of patina. Some rainwater is needed for the patina to form and its rate of development will depend on the water ‘dwell time’ on a surface. So, vertical cladding and sheltered surfaces will take much longer to patinate naturally than exposed roofs and might not turn blue or green over the life- time of the building. Not surprisingly, factory applied surface treatments have been popular for some time to provide straightaway oxidisation and patination of copper surfaces, particularly for facades. Some of the processes involved are very similar

to those taking place over time in the environ- ment and utilise copper mineral compounds, not alien chemical actions. Essentially, they bring for- ward the environmental changes without taking away the integrity of copper as a natural, living material. All these surfaces form an integral part of the copper and are not coatings or paint, and ongoing changes will continue over time depend- ing on the local environment. They include pre-oxidised copper, where the thickness of the oxide layer determines the degree of lightness or darkness, and pre-patination to provide straight- away the blue or green patina that otherwise takes many years to develop in the atmosphere. Pre-patination processes have moved on and

can now enable designers to determine both the colour and intensity of patina for each project with ‘living’ surfaces. As well as a solid patina colour, other intensities can be created revealing some of the dark oxidised background material. ‘Living’ pre-patinated copper was used very successfully on a mixed-tenure housing

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development of 280 apartments on an histori- cally sensitive West London site.

Breaking up the elevations

The design aims to create good modern buildings that relate to the context of this sensitive site. External materials were selected that are durable and have integral, rather than applied, finishes with ‘natural’ hue and colour. The pre-patinated copper was specified to give the finished impres- sion and to blend immediately with the surrounding older buildings. The use of high quality, subtle materials – brickwork, grey roof- ing and pre-patinated copper – aims to soften the visual impact of the buildings. Lift and stair cores are expressed as vertical stacks equivalent to traditional features such as chimneys, emphasised through the green copper cladding. They provide a rhythmic punctuation breaking up the street elevations.

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