An internal monologue on copper

Copper has seen a dramatic change in use from its historic place roofing prestigious buildings to being a thoroughly modern external skin for contemporary architecture. But its role as an interior surfacing material is also growing, presenting new opportunities and challenges, explains architect Chris Hodson

Architectural copper is characterised by the natural development of a distinctive patina with colours changing over time, dependent upon local environmental conditions and air quality. 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 darkens over several years to a chocolate brown. A complex combination of factors determines the nature and speed of development of patina externally. Continued weathering can eventually result in the distinctive green or blue patina seen on older roofs. Some rainwater is needed for the patina to form and its rate of development will depend on the water ‘dwell time’ on each surface.

So, vertical cladding and sheltered surfaces will take much longer to patinate naturally than exposed roofs – while protected areas such as soffits may not patinate at all. Obviously, copper used internally and away from the outside environment will not change and develop in this way. Modern factory-applied surface treatments can provide ‘straightaway’ oxidisation and patination of copper surfaces to a selected level. Essentially, they bring forward the environmental changes without taking away the integrity of copper as a natural, living material and are not coatings or paint. It’s important to remember that on-going changes to pre-oxidised and pre-patinated copper, as well as alloys such as brass and bronze, will continue over time depending on the local environment. Again, this does not generally apply to interior applications. Copper and its alloys already enjoy a long heritage inside buildings, contributing a distinctive tactility to door furniture and handrails, and visual richness to lighting and other fittings. Now they are also used as high-quality coverings for walls, doors, ceilings and other interior surfaces, exploiting the materials’ inherent antimicrobial and fire-safe performance. Internally, copper can be used in a wider range of forms, enjoying freedom from the constraints of weather-proof detailing.

Having said that, material continuity is a recurring architectural theme, with external copper cladding continuing inside, simply separated by glazing. Here, it is essential for designers to understand and, indeed, celebrate the divergent developments of internal and external copper. This approach is demonstrated in a recent commercial HQ redevelopment in Guildford. Here, the updated, glazed entrance atrium now incorporates feature walls – including inset doors – faced with horizontal copper panels, alternating in three different surfaces: bright ‘mill finish’ alongside light and dark brown pre-oxidised copper. Structural columns are similarly enwrapped with alternating finish copper bands and the copper detailing is even continued into elements of bespoke furniture. This internal copper cladding had a post-lacquer finish to arrest further oxidisation, retaining the three colours, protecting the surface and giving a reflective surface. The same horizontal copper panel composition of three surfaces continues past glazing to the outside.

Here, the building’s entrance has been transformed with new copper-clad canopies to create a strong, easily recognised identity. Externally, the copper has not received a lacquer finish, as its architects explain: “We consider copper’s natural surface development outside, reflecting the local environment, to be one of the material’s key attributes. An attractive, gradual weathering and softening of the differentiation between the three different copper surfaces on the canopies has already begun – and will continue over time – as we anticipated.” An alternative approach is to consider today’s wide range of copper surfaces and alloys, material forms and installation systems separately for external or interior applications. And the latest developments in abraded and embossed mechanical surface treatments are particularly suited to interior design, adding another level of ‘close-up’ visual richness, texture and tactility.

This is demonstrated in the redesign and remodelling of a legendary 1980s spa hotel overlooking Lake Lucerne. Externally, it is clad in vertically arranged brass cassettes creating a flat surface, interspersed with generous glazing. Over time, the brass will weather naturally to complement the brown copper facades of the original building. But copper also forms an integral part of the interior design, particularly in the hotel’s grand entrance which welcomes guests with a blend of natural, warm and soft tones. Here, walls and columns are surfaced in continuous copper with a brushed, semi-matt finish. Different copper surfaces are used to highlight fireplaces in individual suites, creating a feeling of richness and warmth. To fully realise the potential of copper and its alloys – both as architectural and interior surfacing materials – designers need to understand their differing characteristics.

The dedicated expertise of copper suppliers will prove to be essential.

Chris Hodson is a member of RIBA and consultant to Aurubis