Copper’s unique architectural qualities are defined by its naturally-developing patina – which cannot be successfully replicated 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 it exceptional longevity.

Natural surface treatments

Today, factory-applied surface treatments can provide oxidisation and patination of copper straightaway to a selected level. This is particularly useful for vertical surfaces that might not otherwise ever develop a blue/green patina. The processes involved are very similar to those taking place in the environment – not alien chemical reactions – to bring forward environmental changes without taking away the integrity of copper as a natural, living material.

These surface treatments form an integral part of the copper and are not coatings or paint. They utilise the same brochantite mineralogy found in natural patinas all over the world. Oxidisation can be light or dark. With pre-patination, the process can be accurately controlled so that, as well as the solid blue/green patina colours, other intensities of patina flecks can be created, revealing some of the dark oxidised background material to give a ‘living’ surface. And, of course, copper alloys – including bronze, brass and a more recent golden material – add to the architectural copper palette.

Forms and systems

Traditionally, copper cladding and roofing utilise thin sheets, or strips, with formed joints and fully supported by a substrate. But modern techniques, such as copper shingles, panels and cassettes, add to its potential. And copper is also being used to clad distinct elements such as fins, screens and brise-soleil. One of the most exciting developments today is experimentation with diverse forms, apart from flat-rolled material. For example, copper can be pressed to provide surface textures and modulation, and perforated, expanded or woven as mesh for transparency.

Combinations of copper’s numerous natural surfaces, diverse forms and innovative installation techniques offer architects new freedom in design materiality, exemplified here with an international selection of contemporary interventions to historic buildings.

Referencing historic building fabric

Part of the transformation of the Old Post Office building (picture 1) in Gothenburg, Sweden, into a luxury hotel, a new 13-storey tower takes literal reference from existing materials. The tower comprises a pair of contemporary monolithic forms, separated by a vertical sliver of glass, one wing clad in patinated copper, the other slate – both materials used on the Old Post Office roof. The architects selected three different intensities of ‘living’ pre-patinated surfaces for the new cladding panels, which pick up on the natural green patina of roof detailing to the original building.

Shared materiality

A different approach was taken with a striking contemporary rooftop extension clad in pre-oxidised brown copper, announcing the rejuvenated Aberdeen Art Gallery (picture 2) – just named winner of the 2021 Andrew Doolan ‘Best Building in Scotland’ Award. It is defined by vertical, scalloped panel facades of brown pre-oxidised copper, some perforated for transparency.

The extension was designed as a sculptural element, responding to the proportions and colours of the existing granite frontages but also reinforcing copper’s historic presence on the city’s civic roofscape. This thoroughly contemporary design approach shares materiality with the buildings’ classical green patina copper dome without copying its colour. Having said that, repairs to the dome itself were carried out using pre-patinated copper, carefully matched to the existing historic patination.

Lunar inspiration

At the heart of the renovation and upgrading of ‘the Moon’ children’s art centre (picture 3) in the Belgian city of Mechelen is a small theatre complex – a golden cube defined by its extraordinary, creased golden copper alloy cladding. Despite its architects’ inspiration by associations with the Apollo 11 Lunar Module and its crumpled golden metal underside, the building’s aesthetic is presented as a contemporary reflection on the intricate stone tracery of the neighbouring medieval cathedral tower.

This innovative alloy of copper with aluminium and zinc gives 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, resulting in a protective matt finish. Over time, it behaves differently from other copper products and does not develop a blue or green patina.

Contextually responsive

Envisaged as a delicate, jewel-like crown, capturing the spirit and excitement of the golden era of film, chevron screens formed from copper tiles announce a contextually responsive Sydney hotel conversion (picture 4). Created from the regeneration of an 80-year-old warehouse, the building regeneration references neighbouring Art Deco buildings and its film precinct location. With some tiles perforated and others tactically omitted, the system comprises three scenarios, adding richness and visual interest.