CPD: Copper shows it’s an ore-inspiring choice

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Shining example: Copper alloy panels at Bristol's Colston Hall music venue provide a striking exterior

Copper roofs feature in the historic skylines of many cities. But today, designers see copper as a modern, sustainable material, says Sandy Harrison.

Copper is widely available in sheets or strips, but prefabricated rolled profiles, shingles, cassettes, flashings, gutters and downpipes are also available. It is easy to form manually or mechanically to suit virtually any three-dimensional shape, including complex curves and details. Roof pitches from 1^o to 90^o can be accommodated. Well-established jointing and forming techniques make it a robust, weatherproof covering for virtually any external surface, offering designers real freedom of architectural form.

For architectural applications, copper is rolled to thicknesses ranging between 0.5 and 3.0mm but a 0.6 or 0.7mm thickness is typical for roofing and 1.5 or 3.0mm for self-supporting curtain walling. Copper can be worked at any temperature and does not become brittle in cold weather (see case study overleaf).

With a thermal expansion value around 50% less than both zinc and lead, properly-designed copper roofs minimise movements due to thermal changes, avoiding deterioration and failure.

The electrical potential of copper is comparatively high, which means that it could form a tiny electrical circuit with certain other metals, causing corrosion to accelerate. Copper can, therefore, cause corrosion to other metals such as steel, aluminium or zinc if there is direct contact between the metals and an electrolyte (such as water) is present. But the copper itself is not affected by the metals.

Furthermore, if rainwater from copper surfaces runs onto other metals with a lower electrical potential, there may be interaction unless they are protected and maintained by established methods. Unaffected metals are lead, stainless steel and brass, which can all be joined to copper without any corrosion problems.

Rainwater running off bitumen exposed to the sun can cause corrosion problems for various materials, including copper, and certain residues washed out of concrete or mortar can cause copper to take on a blue-green colour. Wash-off from red cedar shingles can also cause metals to corrode.

A few coppers: Freya’s Cabin at Kielder Water in Northumberland features Luvata Nordic Gold

Copper installation

The more traditional copper techniques use sheets or strips, jointed using angle standing seams or batten rolls and fully supported on a substrate. A basic plumber’s tool kit will be adequate for small jobs. Other items include swivel bending machines and folding benches for folding 1-2m long copper sheets.

Portable hand-formers, as well as motorised deforming machines with various ancillary tools, are available for drawing and upsetting standing seams for curved areas such as domes. One popular, modern variant is the long-strip method, using preformed “trays” to minimise or eliminate horizontal joints, enabling extensive prefabrication to reduce work at height and cut costs. Machines continue to be developed for factory or site prefabrication, including edging and folding machines for the production of double lock standing seams.

Machines can also form single and double-sided upstands on copper strip in one operation, with variable upstands. 

On some models, the copper strip is delivered from the roller pre-profiled on both sides, with allowance made for lateral transverse expansion within the standing seams. With the increasing popularity of copper, specialist roofing contractors are increasingly investing in mechanisation systems.

Fully supported roofs require a decking underneath and the most common material used is timber, although other materials can be used provided that clips can be fixed securely. An underlay is recommended between the substrate and copper, which can allow movement in the copper, provide a temporary weathering for the building during construction, deal with irregularities on the substrate surface and offer some sound absorption.

Copper is not affected by underside corrosion, a problem which can cause premature failure in some alternative metal roofing materials. It therefore does not require complex ventilation measures and is suitable for use on either non-ventilated or ventilated roofs.

For non-ventilated roofs, adequate vapour control layers should be installed with sufficient insulation. For ventilated roofs, to meet Building Regulations, gaps should be provided at the upper and lower edges of the roof or, if these are not feasible, by formed copper hoods.

Copper cladding

In recent years, copper has grown in popularity as a vertical cladding material. Facade cladding can use either self-supporting copper panels or thinner copper bonded to a substrate. Other techniques are growing in popularity, such as copper shingles that offer a distinctive “fish scale” appearance with shapes including squares and diamonds.

For a more linear appearance, copper panels pre-formed on two sides can be used vertically, horizontally or diagonally. For larger areas of flat copper surface, cassettes are available in squarer proportions with folded edges to all four sides and generally fabricated to suit particular requirements.

A growing range of copper surface finishes and colours offers designers diversity and choice. The natural development of copper patina, with colours changing from bright copper to chestnut brown and eventually to the distinctive blue-green, is one of the material’s unique characteristics. In the open, this patina can take years to develop and in some circumstances may never appear at all – for example on sheltered vertical facades.

One of the most popular recent innovations has been the development of pre-patination treatments to provide a green, textured surface immediately, with similar characteristics to the natural patina. Pre-oxidised copper sheets are also popular and have a darker colour than bright, mill-finished copper.

Copper cladding on Barratt’s Green House at the BRE

Environmental performance

Copper’s environmental credentials are particularly important to designers and contractors. It is a long-life, minimal maintenance material and recycling is an integral part of copper’s long history: today, copper scrap is re-used ad infinitum and around 70% of copper used in architecture is from recycled sources.

The copper industry has worked with BRE to assess the most popular copper-based roofing and facade specifications for consideration in the BRE’s Green Guide, together with the latest Life Cycle Analysis (LCA) data. The Green Guide rates building elements from A+ for best environmental performance to E for the worst within particular specification categories, using LCA techniques.

In 1996, when the Green Guide was first published, all copper-finished roofs and most copper facade specifications achieved A+ or A summary ratings. Where a few cladding specifications had lower ratings, these could be improved easily by replacing particular components – without affecting the copper itself – with more sustainable alternatives.

Copper’s longevity is a major strength in terms of sustainability. This longevity results from the complex patination process, which ensures durability with no maintenance and resistance to corrosion in virtually any atmospheric condition. In this respect, the latest Green Guide is arguably misleading in suggesting low typical replacement intervals that are not justified by experience: some copper roofs are known to have performed well for more than 700 years. The lifespan of copper roofing and cladding is conservatively thought to be around 200 years, subject to substrate and structure.

This longevity has a significant effect on comparative whole of life assessments in terms of carbon emissions, embodied energy and cost. This is illustrated in a comparison of architectural metals considered over whole of life, taken from a 2004 study by Germany’s Fraunhofer Institute. This shows that copper offers the lowest embodied energy compared to stainless steel and aluminium, at 103 megajoules per square metre compared with 157MJ/m² for stainless steel and 115 MJ/m² for aluminium. The same source also shows copper to also have the lowest embodied carbon. 

Sandy Harrison is chairman of Copper in Architecture, part of the European Copper in Architecture Campaign. For more information visit www.copperinfo.co.uk or www.copperconcept.org

Copper alloy mesh cladding at Plymouth Theatre Royal’s TR2 building

Copper’s arctic role in the land of the northern lights

Copper’s capabilities have been tested at the Svalbard Science Centre, halfway between mainland Norway and the North Pole. Here, temperatures as low as -50^oC are encountered during fierce winter storms, the ground is permanently frozen and mid-November to January is spent in total darkness.

So constructing an 8,500m² extension to a university research building presented some unusual challenges, even before considering the “organic” design featuring sloping facades and shallow pitched roofs.

An insulated copper-clad skin is wrapped around the complex spaces demanded by the brief, creating an outer shell adjusted to the wind and driving snow.

Copper was chosen for its flexibility in adapting to complex shapes, as well as its durability, long life and absence of maintenance. Luvata’s mill finish Nordic Standard copper was used throughout.

Roofs are clad with 0.7mm thick copper trays jointed with 50mm high, raised single-lock seams. All the jointing details were preformed in a workshop in minimise work on the roofs and facades themselves.

The project was built by main contractor Skanska and Norwegian company Erling Freitag carried out the copper work. Four sheet metal workers took around a year to install 10,000m² of copper to roofs and facades.

Copper can be worked at all temperatures and, unlike metals such as zinc, does not become brittle and break in cold weather. Work at the Svalbard Science Centre was carried out during biting cold winter storms, but the copper cladding retained good workability even at these extreme temperatures, thereby extending the construction period into the cold season.

Copper installation contractor Svein Freitag said: “Wind chill was the worst aspect as wearing so many clothes made it difficult to move around and work. But the continuous darkness was never a problem – actually the pale blue Arctic light is very beautiful. The project went well overall and we would do it all again if we could.”

In addition to the Nordic Standard copper used at Svalbard, Luvata offers a constantly expanding range of surfaces. Nordic Royal is an alloy of copper using aluminium and zinc to give a permanent, warm golden surface. Pre-patinated Nordic Green Living, meanwhile, offers architects and designers the ability to specify the type and intensity of patina.

www.luvata.com

CPD test paper

An introduction to copper

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