Copper in architecture

Copper 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 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.

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 (6th century) 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 (hospitals, nursing homes, mass transit facilities) as well as in residential buildings because of the public health benefits. (For main article, see: Antimicrobial copper-alloy touch surfaces.)

Craftsmen and designers utilize copper’s inherent benefits to build aesthetically pleasing and long-lasting building systems. From cathedrals to castles and from homes to offices, copper is used in many products: low-sloped and pitched roofs, soffits, fascias, flashings, gutters, downspouts, building expansion joints, domes, spires, and vaults. Copper is also used to clad walls and other surfaces in the exterior and interior environment.

Copper offers a unique character and durability as a roofing material. Its appearance can complement any style of building, from traditional to modern. Its warmth and beauty make it a desirable material for many architects. Copper also satisfies demands of architects and building owners regarding lifetime cost, ease of fabrication, low maintenance, and environmental friendliness.

The installation of copper roofing is a craft requiring experienced installers. Its ductility and malleability make it a compatible material to form over irregular roof structures. It is easy to hammer or work into watertight designs without caulk or gaskets. Domes and other curved roof shapes are readily handled with copper.

When properly designed and installed, a copper roof provides an economical, long-term roofing solution. Tests on European copper roofs from the 18th century showed that, in theory, copper roofs can last one thousand years.

Another advantage of copper roofing systems is that they are relatively easy to repair. For small pits or cracks, affected areas can be cleaned and filled with solder. For larger areas, patches can be cut and soldered into place. For major areas, the affected copper can be cut out and replaced using a flat locked soldered seam.

Copper roofs can be designed to meet or surpass other materials in terms of energy savings. A vented copper roof assembly at Oak Ridge National Laboratories (U.S.) substantially reduced heat gain versus stone-coated steel shingle (SR246E90) or asphalt shingle (SR093E89), resulting in lower energy costs.

Types of copper roofs include:

Standing seam roofing is composed of preformed or field-formed pans. The pans run parallel to the slope of the roof and are joined to adjacent pans with double-locked standing seams. Copper cleats locked into these seams secure the roofing to the deck.

Batten seam roofing consists of copper pans running parallel to the roof slope, separated by wood battens. Battens are covered with copper caps that are loose-locked into adjacent pans to help to secure the roofing. Cleats attached to the battens secure the roofing pans. Transverse seams are required to join ends of preformed pans.

Horizontal seam roofs, also called the Bermuda style, consist of copper pans where the long dimension runs horizontally across a roof, attached to horizontal wood nailers. A step is used at each nailer to allow adjacent pans to lock effectively. The height and spacing of the steps enable different appearances.

A common design for a chevron roof is based on a batten seam construction to which auxiliary battens are attached. With proper design, decorative battens can have almost any shape or size and run in any direction.

Flat locked and soldered seam roofing systems are typically used on flat or low-pitched roofs. They are also used on curved surfaces such as domes and barrel vaults.

Flat seam unsoldered copper roofing is a shingle-like option for high slope applications.

Mansard roofs are used on vertical or nearly vertical surfaces. For the most part, these roofs are based on standing seam or batten seam construction.

Long-pan systems (pans and seam lengths greater than 10-feet) accommodate the cumulative expansion stress over long spans of copper sheets. These installations can be complicated due to the length of roof pan versus seam length, cleat design and spacing, and the physical expansion characteristics of copper sheets. This expansion must be accommodated by fixing the pan at one end (which accumulates the expansion at the loose end) or by fixing the center of the pan (which accumulates half of the expansion at both free ends). In addition to panels, copper roof tiles can add uniqueness to a roofing system. They can be used on any roof shape and in all types of climates.

While most modern construction materials are fairly resistant to moisture penetration, many joints between masonry units, panels, and architectural features are not. The effects of natural movement due to settlement, expansion, and contraction may eventually lead to leaks.

Copper is an excellent material for flashing because of its malleability, strength, solderability, workability, high resistance to the caustic effects of mortars and hostile environments, and long service life. This enables a roof to be built without weak points. Since flashing is expensive to replace if it fails, copper’s long life is a major cost advantage.

Cold rolled 1/8″-hard temper copper is recommended for most flashing applications. This material offers more resistance than soft copper to the stresses of expansion and contraction. Soft copper can be specified where extreme forming is required, such as in complicated roof shapes. Thermal movement in flashings is prevented or is permitted only at predetermined locations.

Flashing installed incorrectly can promote line corrosion and shorten the life of valley flashing, especially in acidic environments. The risk is most prevalent at the leading edge of shingles where the shingle edges rest on the copper flashing.

Through-wall flashing diverts moisture that has entered the wall before it can cause damage. Counterflashing diverts water to the base flashing, which, in turn, diverts it to other materials.

Various types of copper flashings and copings exist. Diagramatic explanations are available.

Gutters and downspouts
Leaking gutters and downspouts can cause serious damage to a building’s interior and exterior. Copper is a good choice for gutters and downspouts because it makes strong leak-proof joints. Gutters and downspouts made with copper are expected to outlast other metal materials and plastics. Even in corrosion-prone seacoast environments or in areas with acid rain or smog, copper gutters and downspouts can provide 50 years or more of service.

Downspouts can be plain or corrugated, round or rectangular. Sixteen- or twenty-ounce cold rolled copper is typically used. Decorative designs are also available.

Hung copper gutters are supported by brass- or copper brackets or hangers, or by brass straps. Copper gutter linings are often built into wood framed supporting structures. Scuppers are used to provide an outlet through parapet walls or gravel stops on flat and built-up roofs to allow drainage of excess water. They can be used in conjunction with gutters and downspouts to divert water flow to the desired location. Copper roof sumps are generally used for draining small roof areas such as canopies. Roof sump drains are not recommended for general roof drainage systems.

One of the disadvantages of copper is its propensity to stain light-colored building materials, such as marble or limestone. Green staining is particularly visible on light-colored surfaces. Lead-coated copper can result in a black or gray stain that may blend well with lighter building materials. Staining can be reduced by collecting runoff in gutters and directing it away from the building via downspouts or by designing drip edges to help reduce the amount of copper laden moisture that comes into contact with material below. Coating the adjacent surface of the porous material with a clear silicone sealant also reduces staining. Staining may not develop in areas of rapid run-off due to the short dwell time of water on the copper.

Domes, spires and vaults
Copper dome made with standing seam copper panels and with a copper finial pineapple mounted on top. The copper finial is handmade from uncoated copper and the pineapple leaves are patinated copper.

There are many types of copper domes, spires, and vaults, both with simple geometries or complex curved surfaces and multi-faceted designs. Examples include circular domes with diagonal flat seam systems, circular domes with standing seam systems, circular domes with flat seam systems, conical spires, flat seam roofing on octagonal spires, standing seam barrel vaults, and flat seam barrel vaults. Information about steps for dome panel layouts and specifications for copper constructions is available.

Wall cladding
Copper cladding has become popular in modern architecture. The technology enables architects to incorporate visually desirable features into their designs, such as embossed or shaped-metal cladding.

Cladding enables structures to be made with much less weight than solid copper. Four millimeter-thick composites weigh 2.08 pounds per square foot, only 35% as much as solid copper of the same thickness.

Copper cladding is used in building exteriors and indoor environments. On building exteriors, copper cladding sheets, shingles, and pre-fabricated panels shield buildings from the elements, acting as first line of defenses against wind, dust, and water. The cladding is lightweight, durable, and corrosion resistant, which is particularly important for large buildings. Common interior applications include lobby walls, soffits, column facings, and interior walls of elevator cabs.

Copper cladding can be cut, routed, sawed, filed, drilled, screwed, welded, and curved to form complex shapes. A variety of finishes and colors are available.

Flat, circular, and unusually shaped walls can be covered with copper cladding. Most are field-formed from sheet material. They can also be pre-manufactured. In addition, engineered systems such as insulated panels, non-insulated honeycomb panels, copper screen panels, and structural wall claddings are available. Horizontal copper siding provides a relatively flat appearance with fine horizontal lines. Beveled copper panels have depth for heavy-shadowed effects. Flat siding has minimal shadows. Structural panels are designed to be attached directly to a wall structure without the use of a continuous substrate. Diagonal flat lock panels are used on curved surfaces, such as domes, spires and vaults. Horizontal flat lock panels are basically identical to flat seam roofing applied on a vertical surface. Copper screen panels are a lightweight finish screen that can be perforated or have shaped openings to function as sun or decorative screens. A copper alloy curtain wall is a non-structural outer building covering that keeps out weather. Composite copper cladding is made by attaching copper sheeting to both sides of rigid thermoplastic sheet.

The former British Overseas Aircraft Corporation headquarters building in Glasgow is clad with copper.

Peckham Library, in London, won the 2000 Stirling Award for Architectural Innovation, the 2001 Copper Cladding Award, and the 2002 Civic Trust Award for excellence in public architecture.
Several different copper facade cladding systems are available:

Seaming technique. This is a vertical or horizontal classical cladding construction used in copper roof and façade designs. Available in sheets and strips, the cladding is fixed with clips. Since water tightness may not be a concern on vertical surfaces, angle standing seams are often sufficient. Double lock standing seams are often not necessary. Links to photographs of horozontal and vertical standing and flat lock seams at the University of Debrecen’s Copper Gateway in Hungary and of pre-oxidized copper clad seamed facades at the Hotel Crowne Plaza Milano, in Milan, Italy, are available.

System shingles. Shingles are pre-manufactured rectangular or square flat tiles for roofs, walls, and individual building components. They have 1800 folds along all four borders – two folds towards the external side and two towards the internal side. The shingles are interlocked during installation. The fastening is hidden with stainless steel or copper clips on wood sheeting or trapezoidal panels. Machine notching and folding ensures that the shingles have uniform dimensions. Links to pictoral examples of copper shingles in an exterior and interior environment are available.

Panels. Panels are sheets of pre-profiled copper with lengths up to 4–5 meters and standard widths up to 500 mm. They are two-sided cladding elements that can be with or without an end base. Assembly is performed using the tongue and groove principle or by overlapping. Panels can be assembled vertically, horizontally, or diagonally. There are three basic forms: tongue and groove panels laid vertically as level surface facade cladding; tongue and groove panels laid horizontally as level surface facade cladding; and custom panels laid in different directions with visible or masked fastening, flush against the surface or overlapping. Links to representative photographs of golden-colored and patinated-green panels are available.

System cassettes. This is a rigid rectangular ventilated wall system consisting of curved or flat metal panels mounted and secured to a supporting structure. All four borders are pre-folded at the factory. Folded edges on every side allow large sheet metal parts to lie even with the cladding surface. Fixing is usually by riveting, screwing, or by using angle brackets or bolt hooks to fix the cassettes directly to the substrate. System cassettes are pre-profiled to meet specific architectural requirements. Links to representative photographs of cassette cladding are available.

Profiled sheets. Profiled sheets are well suited for covering large cladding surfaces without joints because of their regular, unimposing profiles. Available in a wide variety of shapes, they are well-suited for new flat roofs, façade and pitched roofs, and renovation work. Profiles available include: sinusoidal wave corrugated profiles; trapezoidal profiles with various geometries; and custom profiles with special geometry and edges. They can be pre-manufactured and specified with embossed patterns or other designs.

Special shapes. Special shaped façades are available to impart desired visual effects. Perforated metal sheets are available with a variety of shapes (round, square, oblong, etc.) and arrangements (rectangular, diagonal, parallel width, staggered, etc.). They can be designed to create subtle patterns, ‘super graphics,’ and text. Mesh and textile structures are also available. Links to photographs of special-shaped cladded buildings are available.

Building expansion joints
Designing for the movement of building components due to temperature, loads, and settlement is an important part of architectural detailing. Building expansion joints provide barriers to the exterior and cover spaces between components. Copper is an excellent material for expansion joints because it is easy to form and lasts a long time. Details regarding roof conditions, roof edges, floors, are available.

Indoor design

Architectural copper cladding in the interior of the Capital Museum, Beijing, People’s Republic of China.

Copper aesthetically enhances interior wall systems, ceilings, fixtures, furniture, and hardware by evoking an atmosphere of warmth, tranquility, and calm. Regarding performance advantages, it is lightweight, fire resistant, durable, workable, and non-organic (it does not off-gas). Typical copper-based interiors include panels, shingles, screens, ornaments, fixtures, and other decorative enhancements.

Since copper surfaces kill pathogenic microbes, architects who design public facilities, such as hospitals and mass transit facilities, look to copper products as a public health benefit. In recent years, copper countertops, range hoods, sinks, handles, doorknobs, faucets, and furniture embellishments have become trendy – both for their appearance as well as for their antimicrobial properties. (See main article: Antimicrobial copper-alloy touch surfaces).

Copper is joined in indoor environments by butt welding, soldering, rivets, nails, screws, bolting, standing seams, lap seams (with and without fasteners), flat seams, bolted flanges, splines, flush laps, and batten seams.

Green buildings
Sustainable materials are key elements of green buildings. Some benefits of sustainable materials include durability, long life, recyclability, and energy and thermal efficiency. Copper ranks highly in all of these categories.

Copper is one of nature’s most efficient thermal and electrical conductors, which helps to conserve energy. Because of its high thermal conductivity, it is used extensively in building heating systems, direct exchange heat pumps, and solar power and hot water equipment. Its high electrical conductivity increases the efficiency of lighting, electrical motors, fans, and appliances, making a building’s operation more cost effective with less energy and environmental impact.

Because copper has a better thermal conductivity rating than usual façade and roofing materials, it is well-suited to solar thermal façade systems. The first commercial application of a fully integrated solar thermal copper façade system was installed at the Pori Public Swimming Complex in Finland. The installation is an urban example of sustainability and carbon emissions reduction. The solar façade works in conjunction with roof collectors and is supplemented by roof-mounted photovoltaics that provide 120,000 kWh of heat, an amount of energy equivalent to that used annually by six average family houses in cold-climate Finland.

One standard in the United States Green Building Council (USGBC)’s Leadership in Energy and Environmental Design rating system (LEED) requires that newly constructed buildings include materials containing pre- and post-consumer recycled content. Most copper products used in construction (except electrical materials that require highly refined virgin copper) contain a large percentage of recycled content. See: Copper in architecture#Recycling.

Copper and its alloys are readily joined by mechanical techniques, such as crimping, staking, riveting, and bolting; or by bonding techniques, such as soldering, brazing and welding. Selection of the best joining technique is determined by service requirements, joint configuration, thickness of components, and alloy composition.

Soldering is the preferred joining method where strong, watertight joints are required, such as for internal gutters, roofing, and flashing applications. A soldered seam joins two pieces of copper into a cohesive unit that expands and contracts as one piece. Well-soldered seams are often stronger than the original base material and provide many years of service.

Mechanical fasteners, such as screws, bolts, and rivets, are often used to strengthen the joints and seams. Continuous, long runs of soldered seams can cause stress fractures and should therefore be avoided. Common 50-50 tin-lead bar solder is often used for uncoated copper; 60-40 tin-lead solder is used for lead-coated copper. Many lead-free solders are also acceptable.

Adhesives can be used in certain applications. Relatively thin sheet alloys can be bonded to plywood or certain types of foam which act as rigid insulation.

Brazing is the preferred method for joining pipe and tube copper alloys. Copper metal sections are joined with a non-ferrous filler material with a melting point above 800 degrees Fahrenheit but below the melting point of the base metals. Blind or concealed joints are recommended since the color match of silver filler material is fair to poor.

Welding is a process where pieces of copper are effectively melted together, either by flame, electricity, or high pressure. With increasing availability of modern TIG welding equipment, welding of even light-gauge copper decorative elements is gaining acceptance.

Instructional videos are available regarding fluxing and soldering techniques; how to make flat seam solder joints, double-lock standing seams, lap seams, soldering vertical sheet copper lap seams, and stitches (including the butterfly stitch); as well as copper tinning, bending, flaring, and brazing.

Sealants are an alternative to solder where additional strength is not required. In most cases, sealants should not be necessary with a properly designed copper installation. They are at best a relatively short-term solution requiring frequent maintenance. Regardless, sealant-filled joints have been used successfully as a secondary waterproofing measure for standing seam and batten seam roofing applications where low-sloped roofs are less than three inches per foot. Sealants can also be used in joints that are primarily designed to accommodate thermal movement of the copper.

The sealants used should be tested by the manufacturer and designated as compatible for use with copper.

In general, butyl, polysulfide, polyurethane, and other inorganic or rubber-based sealants are reasonably compatible with copper. Acrylic, neoprene, and nitrile-based sealants actively corrode copper. Silicone sealants are somewhat successful with copper but their suitability should be verified before application.

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.

Structural considerations
Structural considerations play an important role in the proper design of copper applications. The primary concern is about thermal effects: movement and stresses related to temperature variations. Thermal effects can be accommodated by preventing movement and resisting cumulative stresses or by allowing movement at predetermined locations, thereby relieving anticipated thermal stresses.

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