Redefining copper

Sometimes we need to look back to understand the dynamics of developments in architectural materials – particularly metals – and where they might lead in the future. Copper cladding is one example with a growing and diverse presence in contemporary design. Chris Hodson, architect and consultant to international copper specialist Aurubis Architectural, explains

One of our oldest building materials, copper displays unique properties and characteristics. We may still think of it in terms of historic city roofscapes but with the modern movement came a transformation from copper’s historic role as a durable roofing material into a flexible architectural skin covering any external surface, including walls. The malleability of copper sheet allows it to be used as a covering for architectural elements of all shapes with minimal constraints. Surfaces can be flat, curved or faceted and used at any inclination or pitch – and in any environment. As a result, architects have focused on copper as a wrapping for building forms with material continuity.

Continuity covering complexity

Built within the Arctic Circle, Jarmund/Vigsnæs’ Svalbard Science Centre exemplifies this approach with its ‘form follows function’ design – informed by wind flow projections – using an external skin of ‘mill-finish’ copper. Designers continue to exploit this capability today, fired by the complex forms made possible and encouraged by CAD and, now, BIM techniques. But, following on from postmodernism, architects are now keen to explore other possibilities of the material as well.

Copper’s continuously changing surface appearance and the natural development of its distinctive patina in the environment still fascinates. Within a few days of exposure to the atmosphere the surface begins to oxidise, changing from the ‘bright’ mill finish to a chestnut brown, which gradually darkens over several years to anthracite. Continued weathering can then result in the appearance of the distinctive green patina – or blue in coastal locations. This patina film provides impressive protection against corrosion and can repair itself if damaged, defining the exceptional longevity of copper cladding, which can be counted in hundreds of years.

New surfaces

A complex combination of factors determines the nature and speed of patination, taking years or even decades to develop naturally. Not surprisingly, factory applied surface treatments have been popular for some time to provide straightaway the brown oxidisation or blue/green patination that occurs in the environment. Far more choice is available today including different levels of brown pre-oxidisation and various intensities of green or blue patina. These new opportunities are demonstrated by modern interventions to the Hotel Post at the heart of Gothenburg, Sweden, animated with rich, striated surfaces of copper panels, patinated to varying levels.

In addition, copper alloys have been used throughout history but bronze and brass are growing in popularity for architectural applications today. Most recently, an innovative alloy of copper with aluminium and zinc adds to the palette with a rich golden through-colour that is very stable. The surface retains its golden colour and simply loses some of its sheen as the oxide layer thickens with exposure to the atmosphere to give a protective matt finish. It behaves differently to other copper products over time and does not develop a blue or green patina.

New forms

Probably the most exciting developments in metals generally today are with new material forms, creating extra dimensions of modulation, texture and transparency for architectural surfaces – and copper is well suited to this approach. Designers are now working with embossed and pressed shapes, and profiled sheets to add an extra dimension, as well as with perforated or expanded sheets and mesh for transparency and veiled effects. This is illustrated in the Deptford Lounge community building, which includes a rooftop sports pitch, wrapped in horizontal, golden copper alloy panels – some exhibiting varying degrees of transparency.

But designers are also working with new installation techniques for different forms of copper. Traditionally, copper has been used as a lightweight, fully supported covering with joints defining ‘bays’, determining its structured look. A more modern interpretation is the ‘long strip’ system where copper trays up to around 10m in length eliminate cross-welts, creating a strong linear appearance.

New systems

More recently, other, generally prefabricated and self-supporting, systems have appeared. For facades, copper panels pre-formed on two sides can be used vertically, horizontally or diagonally. For larger flat areas, cassettes have squarer proportions with folded edges to all four sides, while shingles offer a distinctive ‘fish scale’ appearance with shapes including squares, diamonds and rhomboids. These installation techniques or systems give ‘grain’ and structure to the external skin of a building, helping to define its character.

Today, we can see that copper is effectively being redefined in terms of new surfaces, forms and systems and how they can be combined. There is a real impetus for more exploration of the wider design opportunities offered by copper and its alloys for contemporary architecture, with a definite sense of freedom, and this is driven by architects.