page_title: Copper in architecture
section_title: Corrosion resistance
hierarchical_section_title: Copper in architecture / Benefits / Corrosion resistance
caption_attribution_description: Kresge Auditorium, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts. Architect Eero Saarinen, 1954. Detail of roofline. Photograph by me, August 2005.
context_page_description: 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.
context_section_description: 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 (¹⁄₆₄ in) 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.
caption: Detail of roofline at Kresge Auditorium, Massachusetts Institute of Technology, in the U.S.
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