The history of copper in architecture can be linked to its durability, corrosion resistance, prestigious appearance, and ability to form complex shapes. For centuries, craftsmen and designers utilized these attributes to build aesthetically pleasing and long-lasting building systems.
For the past quarter century, copper has been designed into a much wider range of buildings, incorporating new styles, varieties of colors, and different shapes and textures. Copper clad walls are a modern design element in both indoor and outdoor environments.
Some of the world's most distinguished modern architects have relied on copper. Examples include Frank Lloyd Wright, who specified copper materials in all of his building projects; Michael Graves, an AIA Gold Medalist who designed over 350 buildings worldwide; Renzo Piano, who designed pre-patinated clad copper for the NEMO-Metropolis Museum of Science in Amsterdam; Malcolm Holzman, whose patinated copper shingles at the WCCO Television Communications Centre made the facility an architectural standout in Minneaoplis; and Marianne Dahlbäck and Göran Månsson, who designed the Vasa Museum, a prominent feature of Stockholm’s skyline, with 12,000-square metres copper cladding. Architect Frank O. Gehry’s enormous copper fish sculpture atop the Vila Olimpica in Barcelona is an example of the artistic use of copper.
Copper’s most famous trait is its display from a bright metallic colour to iridescent brown to near black and finally to a greenish verdigris patina. Architects describe the array of browns as russet, chocolate, plum, mahogany, and ebony. The metal’s distinctive green patina has long been coveted by architects and designers.
This article describes practical and aesthetic benefits of copper in architecture as well as its use in exterior applications, interior design elements, and green buildings.
Benefits
Corrosion resistance
As an architectural metal, copper provides excellent corrosion resistance. Copper surfaces form tough oxide-sulfate patina coatings that protect underlying copper surfaces and resist corrosion for a very long time.
Copper corrodes at negligible rates in unpolluted air, water, de-aerated non-oxidizing acids, and when exposed to saline solutions, alkaline solutions, and organic chemicals. Copper roofing in rural atmospheres corrodes at rates of less than 0.4 mm in 200 years.
Unlike most other metals, copper does not suffer from underside corrosion that can cause premature failures in roofing. With a copper roof, supporting substrates and structures usually fail long before the copper on the roof.
Architectural copper is, however, susceptible to corrosive attack under certain conditions. Oxidizing acids, oxidizing heavy-metal salts, alkalis, sulfur and nitrogen oxides, ammonia, and some sulfur and ammonium compounds can expedite copper corrosion. Precipitation in areas with a pH less than 5.5 may corrode copper, possibly before a patina or protective oxide film has the time to form. Acidic precipitation, known as acid rain, is due to emissions from fossil fuel combustion, chemical manufacturing, or other processes that release sulfur and nitrogen oxides into the atmosphere. Erosion corrosion may occur when acidic water from a non-copper roof that does not neutralise the acidity, such as tile, slate, wood, or asphalt, falls on a small area of copper. Line corrosion can occur if the drip edge of an inert roofing material rests directly on copper. A solution to this may be to raise the lower edge of the shingles with a cant strip, or to provide a replaceable reinforcing strip between the shingles and the copper. Proper water-shedding design and detailing, which reduces the dwell time of acidic water on metal surfaces, can prevent the majority of atmospheric corrosion problems.
Brass, an alloy of copper and zinc, has good resistance to atmospheric corrosion, alkalis, and organic acids. In some potable waters and in seawater, however, brass alloys with 20% or more zinc may suffer corrosive attack.
Durability/long-life
Copper roofs are extremely durable in most environments. They have performed well for over 700 years, primarily because of the protective patina that forms on copper surfaces. Tests conducted on 18th Century copper roofs in Europe showed that, in theory, they could last for one thousand years.
Low thermal movement
Properly designed copper roofs minimize movements due to thermal changes. Copper’s low thermal expansion, 40% less than zinc and lead, helps to prevent deterioration and failure. Also, copper’s high melting point ensures that it will not creep or stretch as some other metals do.
On small gable roofs, thermal movement is relatively minor and usually is not an issue. On wide-span buildings over 60 meters and when long panels are used, an allowance for thermal expansion may be necessary. This enables the roof to "float" over supporting substructures while remaining secure.
Low maintenance
Copper does not require cleaning or maintenance. It is particularly suited for areas that are difficult or dangerous to access after installation.
Lightweight
When used as a fully supported roof covering, copper is half the weight (including substrate) of lead and only a quarter of tiled roofs. This generally provides savings in supporting structure and materials costs. Copper cladding offers additional opportunities to reduce the weight of copper structures (For more details, see: Copper cladding and Wall cladding).
Ventilation
Copper does not require complex ventilation measures. It is suitable for both unventilated ‘warm’ and ventilated ‘cold’ roof constructions.
Radio frequency shielding
Sensitive electronic equipment are vulnerable to interference and unauthorized surveillance. These products also require protection from high voltages. Radio frequency (RF) shielding can address these issues by reducing the transmission of electric or magnetic fields from one space to another.
Copper is an excellent material for RF shielding because it absorbs radio and magnetic waves. Other useful properties for RF shielding is that copper has a high electrical conductivity, is ductile, malleable, and solders easily.
RF shielding enclosures filter a range of frequencies for specific conditions. Properly designed and constructed copper enclosures satisfy most RF shielding needs, from computer and electrical switching rooms to hospital CAT-scan and MRI facilities. Special attention needs to be addressed regarding potential shield penetrations, such as doors, vents, and cables.
A shield can be effective against one type of electromagnetic field but not against another. For example, a copper foil or screen RF shield will be minimally effective against power frequency magnetic fields. A power frequency magnetic shield could offer little reduction of radio frequency fields. The same is true for different RF frequencies. A simple large-mesh screen shield can work well for lower frequencies, but can be ineffective for microwaves.
Copper galleon finial.
Sheet copper for RF shielding can be formed into essentially any shape and size. Electrical connection to a grounding system provides an effective RF enclosure.
Lightning protection
Lightning strike protection minimizes damage to buildings during lightning terminations. This is usually accomplished by providing multiple interconnected pathways of low electrical impedance to the ground.
Copper and its alloys are the most common materials used in residential lightning protections, however in industrial, chemically corrosive environments, the copper may need to be clad in tin. Copper effectively facilitates the transmission of lightning energy to the ground because of its excellent electrical conductivity. Also, it bends easily compared to other conductor materials.
When copper roofing, gutters, and rain leaders are electrically bonded to an earth termination facility, a pathway of low electrical impedance to ground is provided, however without dedicated conduction pathways to concentrate the discharge channel, a disperse energized surface may not be the most desirable.
Because copper has a higher electrical conductivity than aluminium and its impedance during a lightning termination is less, copper allows for the use of less cross-sectional surface area per linear length, in its woven wires pathway than does aluminum. Also, aluminium cannot be used in poured concrete or for any component underground due to its galvanic properties.
To be effective, lightning protection systems generally maximize the surface area contact between the conductors and the earth through a ground grid of varying designs. To supplement grounding grids in low-conductivity earth, such as sand or rock, long, hollow copper tubes filled with metallic salts are available. These salts leach through holes in the tube, making the surrounding soil more conductive as well as increasing the overall surface area which decreases effective resistance.
Copper roofs may be used as part of a lightning protection scheme where the copper skin, gutters and rainwater pipes can be linked and bonded to an earth termination facility. The thickness of copper specified for roofing materials is usually adequate for lightning protection. A dedicated lightning protection system may be recommended to adequate lightning protection with an installed copper roof system. The system would include air terminals and intercepting conductors on the roof, a system of ground electrodes, and a system of down-conductors connecting the roof and ground components. It is recommended that the copper roof be bonded to the system of conductors. Bonding ensures that the conductors and roof remain at equipotential and reduce side flashing and possible roof damage.
Wide range of finishes
It is sometimes desirable to chemically alter the surface of copper or copper alloys to create a different color. The most common colors produced are brown or statuary finishes for brass or bronze and green or patina finishes for copper. Mechanical surface treatments, chemical coloring, and coatings are described elsewhere in this article at: Finishes.
Design continuity
Architects often look to architectural copper for continuity in design elements. For example, a copper roofing system may be designed with copper flashings, weatherings, vents, gutters, and downpipes. Cover details may include cornices, moldings, finials and sculptures.
With the growing use of vertical cladding, vertical and roofing surfaces can run into each other so that complete continuity of material and performance is maintained. Rain screens and curtain walling (often linked with transoms and mullions) are also gaining popularity in modern architectural design.
Antimicrobial
Extensive worldwide tests have proved that uncoated copper and copper alloys (e.g., brass, bronze, copper nickel, copper-nickel-zinc) have strong intrinsic antimicrobial properties with efficacies against a wide range of disease-resistant bacteria, molds, fungi and viruses. After years of testing, the U.S. approved the registration of over 300 different copper alloys (copper, brasses, bronzes, copper-nickels, and nickel-silvers) as antimicrobial materials. These developments are creating markets for antimicrobial copper and copper alloys in interior architecture. To meet the design needs for building surfaces, structures, fixtures, and components, antimicrobial copper-based products are available in a wide range of colors, finishes, and mechanical properties. Copper handrails, counter tops, hallways, doors, push plates, kitchens, and bathrooms are just some of the antimicrobial products approved for hospitals, airports, offices, schools, and army barracks to kill harmful bacteria. See: a list of products approved in the U.S.
Sustainability
While a universally accepted definition of sustainability remains elusive, the Brundtland Commission of the United Nations defined sustainable development as development that meets the needs of the present without compromising the ability of future generations to meet their own needs. Sustainability, the long-term maintenance of responsibility, requires the reconciliation of environmental, social equity and economic demands. These "three pillars" of sustainability encompass the responsible management of resource use. Also, it can mean that we can use a resource which won't cease to be abundant despite increasing intake.
Copper is a sustainable material. Its durability offers long service with little maintenance. Its high electrical and thermal energy efficiencies reduce the waste of electrical energy. Its antimicrobial properties destroy pathogenic microorganisms that cause disease. And its high scrap value and ability to be continuously recycled without any loss in performance ensure its responsible management as a valuable resource.
Life cycle inventory (LCI) information on copper tube, sheet, and wire products, using ISO standards and covering the mining and primary copper production sectors (i.e., smelting and refining) is available. Used in life cycle assessments (LCAs), particularly in the building and construction sector, LCI datasets assist manufacturers of copper-containing products with compliance and voluntary improvement initiatives. They also support policy makers in the development of environmental guidelines and regulations with the aim of fostering sustainable development.
The long lifetime of copper roofing and cladding has a significant positive effect on whole life assessments of copper versus other materials in terms of embodied energy consumption (i.e., the total energy consumed during every phase of each lifecycle in MJ/m2), CO2 generation, and cost.
Comparison of lifespan, embodied energy, and embodied CO2 emissions of copper, stainless steel, and aluminum in roofing and cladding materials. (Source: German Ministry for Environmental Affairs, 2004)
| Copper | Stainless steel | Aluminum | |
|---|---|---|---|
| Typical thicknesses (mm) | 0.6 | 0.4 | 0.7 |
| Lifespan (years) | 200 | 100 | 100 |
| Embodied Energy (MJ/m2) | 103.3 | 157.2 | 115.4 |
| CO2 equivalent emissions (kg/m2) | 6.6 | 10.9 | 7.5 |
Recyclability
Recyclability is a key factor of a sustainable material. It reduces the need to mine new resources and requires less energy than mining. Copper and its alloys are virtually 100% recyclable and can be recycled infinitely without any loss of quality (i.e., copper does not degrade (i.e., downcycle) after each recycling loop as do most non-metallic materials, if they are recyclable at all). Copper retains much of its primary metal value: premium-grade scrap normally contains at least 95% of the value of primary metal from newly mined ore. Scrap values for competing materials range from about 60% down to 0%. And copper recycling requires only around 20% of the energy needed to extract and process primary metal.
Currently, around 40% of Europe’s annual copper demand and about 55% of copper used in architecture come from recycled sources. New copper coil and sheet often have 75%-100% recycled content.
By 1985, more copper was recycled than the total amount of copper that was consumed in 1950. This is due to the relative ease of reusing processing waste and salvaging copper from products after their useful life.
Cost effectiveness
Performance, maintenance, service life, and recovery costs from recycling are factors that determine the cost effectiveness of building components. While copper’s initial cost is higher than some other architectural metals, it usually does not need to be replaced during the life of a building. Due to its durability, low maintenance, and ultimate salvage value, the additional cost for copper may be insignificant over the life of a roofing system.
Copper roofing is considerably less expensive than lead, slate, or hand-made clay tiles. Its costs are comparable with zinc, stainless steel, aluminum and even some clay and concrete tiles when considering overall roofing costs (including structure).
Some studies indicate that copper is a more cost-effective material on a life cycle basis than other roof materials with a lifetime of 30 years or more. A European study comparing roofing costs of copper with other metals, concrete and clay tiles, slate, and bitumen found that in the medium to long-term (for lives of 60 to 80 years and 100 years and over), copper and stainless steel were the most cost effective roofing materials of all materials examined.
Installation techniques such as prefabrication, in-situ machine forming, mechanized seaming, and the long-strip system help to reduce the installation costs of copper roofing. By lowering installation costs, these techniques permit designers to specify copper into a wider array of building types, not just large prestigious projects as had been common in the past.
Since scrap copper retains much of its primary value, copper’s life cycle costs are reduced when accounting for its salvage value. For more information, see Recyclability section in this article.
Pure vs. alloyed copper
Pure copper. Unlike other metals, copper is frequently used in its pure (99.9% Cu) unalloyed form for sheet and strip applications in roofing, exterior cladding, and flashing.
Tempering is a heat treatment technique used to increase the toughness of metals. Tempers determine the ductility of the metal, and therefore how well it forms and will hold its shape without additional support. In the U.S., copper is available in six tempers: 060 soft, 1/8 hard cold rolled, 1/4 cold rolled high yield, half hard, three quarter hard, and hard. In the U.K., only three designations exist: soft, half-hard, and hard. Copper and its alloys are defined in the U.S. in Standard Designations for Copper and Copper Alloys by ASTM; in Europe by BS EN 1172: 1997 - 'Copper and Copper Alloys in Europe’; and in the U.K. by the British Standard Code of Practice CP143: Part12: 1970.
Cold rolled copper temper is by far the most popular in building construction in the U.S. It is less malleable than soft copper but is far stronger. Cold rolled 1/8-hard tempered copper is often recommended for roofing and flashing installations. Roof sheets with higher tempers may be specified for certain applications.
Soft tempered copper is extremely malleable and offers far less resistance than cold rolled copper to the stresses induced by expansion and contraction. It is used for intricate ornamental work and where extreme forming is required, such as in complicated thru-wall flashing conditions.
The major use for high-yield copper is in flashing products, where malleability and strength are both important.
The thickness of sheet and strip copper is measured by its weight in ounces per square foot. Thicknesses commonly used in construction in the U.S. are between 12ounces and 48 ounces. Since the industry often uses gauge numbers or actual thicknesses for sheet metal or other building materials, it is necessary to convert between the different measurement systems.
In Europe, phosphorus de-oxidized non-arsenical copper is used with the designation C106. The copper is rolled to thicknesses ranging between 0.5 and 1.0 millimeters (1.5 - 3.0 millimeters for curtain walling) but a 0.6 - 0.7 millimeters thickness is usually used for roofing.
Alloyed copper. Copper alloys, such as brass and bronze, are also used in residential and commercial building structures. Variations in color stem primarily from differences in the alloy chemical composition.
Some of the more popular copper alloys and their associated Unified Numbering System (UNS) numbers developed by ASTM and SAE are as follows:
| Copper alloy | Common term | Composition | Natural color | Weathered color |
|---|---|---|---|---|
| C11000 / C12500 | Copper | 99.90% copper | Salmon red | Reddish-brown to gray-green patina |
| C12200 | Copper | 99.90% copper; 0.02% phosphorus | Salmon red | Reddish-brown to gray-green patina |
| C22000 | Commercial bronze | 90% copper; 10% zinc | Red gold | Brown to gray-green patina in six years |
| C23000 | Red brass | 85% copper; 15% zinc | Reddish yellow | Chocolate brown to gray-green patina |
| C26000 | Cartridge brass | 70% copper; 30% zinc | Yellow | Yellowish, gray-green |
| C28000 | Muntz metal | 60% copper; 40% zinc | Reddish yellow | Red-brown to gray-brown |
| C38500 | Architectural bronze | 57% copper; 3% lead; 40% zinc | Reddish yellow | Russet brown to dark brown |
| C65500 | Silicon bronze | 97% copper; 3% silicon | Reddish old gold | Russet brown to finely mottled gray-brown |
| C74500 | Nickel silver | 65% copper; 25% zinc; 10% nickel | Warm silver | Gray-brown to finely mottled gray-green |
| C79600 | Leaded nickel silver | 45% copper; 42% zinc; 10% nickel; 2% manganese; 1% lead | Warm silver | Gray-brown to finely mottled gray-green |
Further information on architectural copper alloys is available.
Selection criteria
The criteria by which copper and copper alloys are selected for architectural projects include color, strength, hardness, resistance to fatigue and corrosion, electrical and thermal conductivity, and ease of fabrication. Appropriate thicknesses and tempers for specific applications are essential; substitutions can lead to inadequate performance.
Architectural copper is generally used in sheet and strip. Strip is 24-inches or less in width, while sheet is over 24-inches in width, up to 48-inches in width by 96- or 120-inches long, plus in coil form.
Source From Wikipedia
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