Timeless architectural copper

Copper continues to intrigue and inspire architects. With limitless possibilities for innovative contemporary design, copper also provides exemplary recyclability, sustainability and longevity explains Chris Hodson from Aurubis

As one of our oldest building materials, copper’s unique, timeless architectural qualities are defined by its naturally changing patina – which cannot be successfully replicated using other materials with surface coatings. The patina film provides impressive protection against corrosion and can repair itself if damaged, giving it exceptional longevity. 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.

Developing visual characteristics

Continued weathering can then result in development of the distinctive green patina – or blue in coastal locations. This process is an expression of the metal’s propensity to revert to mineral compounds that resemble the ore from which it originally came. Some rainwater is needed for the patina to form and its rate of development will depend on the water “dwell time” on a surface. As a result, vertical cladding and sheltered surfaces will take much longer to patinate naturally than exposed roofs.

Airborne pollution also increases the rate of patination, which therefore takes longer in more remote, cleaner environments than in cities or industrial areas. The complex combination of factors determines the nature and speed of development of patination, giving copper unique, living visual characteristics developing over time in response to local conditions.

Natural material

Today, factory-applied surface treatments can provide oxidisation and patination of copper straight away to a selected level. This is particularly useful for vertical surfaces which 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. They 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, and 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. In addition to all these natural surfaces, copper alloys – including Bronze, Brass and a more recent golden material – add to the architectural copper palette.

For restoration projects, unique pre-patinated copper material can now be produced to match the naturally patinated copper on a building. An original sample from the building is used but initial development can be started with photographs. Often, the original copper removed from a project can be recycled for reuse on the same building.

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.

Sustainability credentials

Combinations of these numerous natural surfaces, diverse forms and innovative installation techniques offer architects a new design freedom – enhanced by copper’s exemplary sustainability credentials. Copper is a natural element within the earth’s crust which has been incorporated into living organisms throughout the evolutionary process. It is non-toxic and its inherent antimicrobial qualities make it ideal for touch surfaces, including interiors.

As a lightweight and flexible covering in buildings, structural support demands are reduced, resulting in lower carbon and ‘whole of life’ costs. Then, at the end of a building’s life, copper retains a high scrap value which drives recovery and recycling. In fact it 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.

And it requires no decoration, maintenance or cleaning – saving resources, cleaning chemicals and cost. Its interaction with the environment has been assessed under the European Reach chemical policy and has no classification/restriction. With an ‘A1 (non-combustible material)’ fire classification to EN 13501-1, copper is suitable for cladding tall buildings, using appropriate constructions. Low thermal movement makes it safe and straightforward to use in any climates and locations.

Chris Hodson is an architect, writer and consultant to Aurubis