Myths and misconceptions regarding copper: It is amazing how many people in the construction field believe: Copper expands more than other metals Copper is a soft, weak metal Copper attracts lightning. NONE of these Myths are correct.
The Science: The coefficient of expansion for copper (0.0000098 per degree F) is the same as that of type 302/304 stainless steel; the coefficient for aluminum is 50 percent greater (0.0000138) while coefficient for zinc is almost double that of copper (0.0000164). Of the materials commonly used for gutters, only mild steel (galvanized, Galvalume, etc.) has a lower coefficient of expansion than copper (0.0000070).
When subjected to temperature changes gutters must transfer expansion movement from a fixed point (outlet or downspout) to a point of release (an expansion joint) without buckling. The ability of a gutter to do this is a function of its columnar strength.
During the early 1940s Revere Copper of Rome, N.Y., conducted tests that established the columnar strength of a gutter is dependent on its temper, thickness and shape. When a copper gutter is properly designed and correctly installed, it has more than enough strength to withstand the forces of nature without failure.
It is true that copper conducts electricity (as does aluminum) but, it does NOT attract it! If a copper roof is struck by lightning, it is typically because it is the tallest/highest item in the immediate area — not because it is copper.
The case for Copper Gutters
Lets take a look at some of the reasons a contractor, architect and building owner should insist on copper rainwater goods: durability, compatibility, self-healing properties, harsh environmental exposures, multiple sources and methods of fabrication, large selection of products and styles, custom designs, environmental issues, recycled value and, of course, cost.
Durability: With the possible exceptions of adobe, thatch and stone, no building material in common use today has a longer or better track record than copper. It is unclear when copper was first used for gutters but, at least 3,000 years before the great cathedrals of Europe were rising (many with copper roof, flashings, and gutters), the Egyptians used wrought copper pipe to transport water at a burial complex located in Abusir
in Northern Egypt. (The pipes, believed to date from the reign of King Sahure, the second King of Egypts 5th Dynasty, who ruled from 2517 to 2505 B.C., were discovered during a 1994 archeological dig.)
Compatibility: When selecting roof flashings and gutters there are at least two compatibility issues to consider:
1) Will the expected life of the flashings and gutter be at least equal that of the roof?
2) Is run-off from the roof (and flashings) compatible with the gutter?
What is the sense in installing a high-end slate (real or simulated), tile, architectural-grade shingle or other 50- to 100- (or more) year roof, if the flashings are made of a material that is subject to corrosion (unless it is maintained with paint or other coating)?
What is the best material for flashing high-end roofs? — Hands down it is copper!
Copper is a noble metal at the high-end of the galvanic series. In this position, copper is highly resistant to corrosion from other materials. However, run-off from copper will attack metals at the lower end of the series: aluminum, mild steel, galvanized steel, Galvalume and zinc.
Self-healing properties: Unlike painted products, if left alone, the aesthetics of copper are self-healing.
Scratches, nicks and other physical damage that expose the unprotected base metal of aluminum or steel gutters must be repaired (field painted or replaced) or corrosion may follow. Similar damage to copper rainwater goods is not a problem.
Within a very short time period (hours), of being exposed to the atmosphere copper begins to oxidize. As time progresses the oxide film builds and thickens to protect the copper from further deterioration. Depending upon the severity of the scratch or ding, age of the copper, how far its natural patination process has progressed and the local weathering factors, the damage may disappear within a few weeks or months.
The important thing, however, is that copper requires no help or maintenance to preserve its aesthetics and weather-proofing function.
Harsh environmental exposures: No metal is better suited for use in marine and harsh urban or industrial environments than copper. Rather than review long dissertations on the tests to determine the durability of copper just consider the Statue of Liberty.
On October 28, 2011, Lady Liberty will celebrate her official 125th birthday. For all that time she has stood in one of the harshest urban, industrial, marine environments in the world — New York Harbor.
Large selection of products and styles: The majority of copper rainwater goods are fabricated from plain, red copper. However, for aesthetic purposes other finishes are available from the copper mills. These include tin/zinc alloy coated copper and pre-oxidized copper.
Eventually all newly exposed plain or red copper will develop a uniform brown or bronze coloration, the rate at which this color forms is dependent on local (micro) environmental conditions and degree or severity of exposure. All other things being equal, sloping surfaces (roofs) age faster than vertical surfaces (walls and downspouts) which, in turn, weather faster than soffits, the bottoms of gutters, and other reverse slope applications.
While the natural oxidation process used to create ContinentalBronze only turns the clock ahead, in the case of gutter bottoms, downspouts and other sheltered locations, the time may be significant.
Custom designs: No architectural metal is easier to cut, bend and solder than copper. As a result, architectural sheet metal shops will be happy to produce custom gutters, collection boxes, leader heads, downspouts and other decorative and functional rainwater control devices out of copper. Many contractors not only work with copper as a business, but design and create interesting artworks as a hobby!
Environmental issues: Despite myths and misconceptions to the contrary, architectural copper is an environmentally friendly material. In fact, because of its source, manufacturing process, durability, recyclable properties and appearance, copper has been referred to as The first green metal (literally and figuratively).
Recycled value: Recycling and reusing copper and copper alloys is not a new, 21st century idea.
This continuous process of use, recycle and re-use of copper is not only possible but also practical because copper is easy to work with and does not down-cycle. Smelting and refining is not required to convert clean, bare-bright copper scrap into new, high quality sheets and coils for the construction, electrical and other markets.
As a result, nearly all of the copper that has been mined (from the Bronze Age to the present) is believed to still be in service today.
Cost: If a copper drainage system is correctly designed and correctly installed, it can provide many decades (centuries?) of maintenance-free and trouble-free service. The first cost of the system will be its last cost.
When the structure serves it useful life and is demolished or is modified in such a manner that the original rainwater system is of no further use, the copper will be salvaged and recycled. While it is impossible to predict the future value of copper, in the past, when 50- to 100-year old copper was recycled its value often exceeded its original cost.
Source: Anne Schade, Revere Copper
Anne Schade is the manager, architectural services at Revere Copper Products, Rome, N.Y.