Copper in architecture
has earned a respected place in the related fields of architecture, building construction, and interior design. From cathedrals to castles and from homes to offices, copper is used for a variety of architectural elements, including roofs, flashings, gutters, downspouts, domes, spires, vaults, wall cladding, and building expansion joints.
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 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 noteworthy aesthetic trait is its range of hues, 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.
History
Copper has played a role in architecture for thousands of years. For example, in ancient Egypt, massive doors to the temple of Amen-Re at Karnak were clad with copper. In the 3rd Century B.C., copper roof shingles were installed atop of the Lowa Maha Paya Temple in Sri Lanka. And the Romans used copper as roof covering for the Pantheon in 27 B.C.Centuries later, copper and its alloys were integral in medieval architecture. The doors of the Church of the Nativity at Bethlehem are covered with plates of bronze, cut out in patterns. Those of Hagia Sophia at Constantinople, of the 8th and 9th century, are wrought in bronze. Bronze doors on the Aachen Cathedral in Germany date back to about 800 A.D. Bronze baptistery doors at the Cathedral of Florence were completed in 1423 A.D. by Ghiberti.
The copper roof of Hildesheim Cathedral, installed in 1280 A.D., survives to this day. And the roof at Kronborg, one of northern Europe's most important Renaissance castles that was immortalized as Elsinore Castle in Shakespeare's Hamlet, was installed in 1585 A.D. The copper on the tower was renovated in 2009.
For years, copper was reserved mainly for public institutions, such as churches, government buildings, and universities. Copper roofs are often one of the most architecturally distinguishable features of these structures.
Today, architectural copper is used in roofing systems, flashings and copings, rain gutters and downspouts, building expansion joints, wall cladding, domes, spires, vaults, and various other design elements. Simultaneously, the metal has evolved from a weather barrier and exterior design element into indoor building environments where it is changing the way commercial and residential interiors are decorated.
In the 21st century, the use of copper continues to evolve in the indoor environment. Its recently proven antimicrobial properties reduce pathogenic bacterial loads on such products as handrails, bedrails, bathroom fixtures, counter tops, etc. These antimicrobial copper-based products are now being incorporated into public facilities as well as in residential buildings because of the public health benefits. ''''
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 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.
File:Kresge Auditorium, MIT.JPG|thumb|left|Detail of roofline at Kresge Auditorium, Massachusetts Institute of Technology, in the U.S.
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 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 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 ''.''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 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.
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
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.