ABSTRACT In terms of durability, few offerings in the construction market even approach the service life expectancy of a properly installed . Much of this durability is corroborated by the preference for copper as a through-wall flashing for various wall assemblies. Indeed, copper roofing is often the benchmark for life-cycle analysis. Copper enjoys obvious architectural appeal; however, it is unique among the , and its use on any project merits consideration of these attributes and limitations. This article focuses on such aspects, with discussion on avoidance of

opper is the oldest low strength, heavier gauge material was stronger and is by far the most popular known to man.1 Few con­ required. Accordingly, soft-temper copper is variety of copper now used in construction. sumers understand the not recommended for most building appli­ The tempering windows are quite wide, chemistry and physics of cations. and they overlap. That is, if a particular mill copper cladding, but they do With the development many years ago of is making half hard at the high end, the seem eager to express opin­ cold-rolled copper, the gauge of the materi­ product may resemble three-quarter hard ionsC regarding how it looks. Copper has low al could be lightened without compromising in terms of its final engineering properties. “columnar rigidity.” There is nothing partic­ its function. Cold-rolled temper is less mal­ Dead-soft tempering is easy to work with, ularly wrong with this property, but cau­ leable than soft temper but is much but it literally droops when held. tions must be observed to avoid unappealing aesthetics and substan­ dard performance. Like several other metals, copper is tem­ pered at the mill to increase its hardness and toughness. If the sheet form complies with ASTM B 370, it consists of 99.9 percent copper and is available in six tempers. These are 060 (soft), H00 (cold-rolled, one-eighth hard), H01 (cold-rolled, high yield), H02 (half hard), H03 (three-quarter hard), and H04 (hard). Soft-temper copper is extremely mal­ leable and best suited for applications such as in ­ tricate ornamental work. It was historically used in building construction; Figure 1 – Introducing flat pans onto a curved surface can and will produce surface undulations. On curves however, because of its having a long radius, the susceptibility is lower.

F EBRUARY 2009 I NTERFACE • 5 Figure 3 – The author (years ago) atop a curved copper roof having no ridge interruption (the nature of safety gear shown can probably date the image). This roof continues to serve satisfactorily on a corporate headquarters facility.

Figure 2 – Almost any metal roof will exhibit some oil canning in direct angles of sunlight. The displeased party should exercise patience, as the eventual patina will obscure most of the oil canning.

In general, cold-rolled, one-eighth hard oversimplification, since weathering copper is recommended for roofing and may exhibit a wide spectrum of flash ing applications. Soft copper may be unusual colors for a number of rea­ used where extreme forming is required, sons as set out by Hunt.5 He postu­ such as in complex through-wall flashings. lates that, due to microclimates and lative dimensional change experienced by However, the cold-rolled version offers far other variables, a metal roof may not be long individual pans. more resistance than does soft to the weathering as intended, but it is probably Curiously, this movement behavior stresses induced by expansion and contrac­ weathering normally for its environment. takes quite a departure on curved surfaces tion. Copper sheet of higher temper should Copper moves – it is inherent in the (Figure 3). From the previous discussion be specified only if indicated for specific chemistry and cannot be dismissed. With about columnar rigidity, thermal movement engineering applications requiring such long panel runs (40 ft and beyond), the (which cannot be stopped) is accommodated properties.2 magnitude of movement becomes consider­ on curved surfaces by slight upward flexure Panel width, fluting, swaging, tension- able. Haddock postulates: of panels between clips. Accordingly, long leveling, seam height, and sheet gauge all panel runs can be used without a ridge have bearing on the tendency toward sur­ A dark-colored panel with low gloss detail (appealing to architects who desire face distortions, also called “oil canning.” at right angle to the summer sun the uninterrupted contours of barrel or Introducing flat pans onto a curved surface can approach temperatures of 200 curved roofs).7 can and will produce surface undulations degrees F. In cold winter nighttime The importance of soldering cannot be (Figure 1). On curves having a long radius, scenarios, the low extremes of sur­ overstated. Especially for low-slope, flat- the susceptibility is lower, but almost any face temperature can actually dip seamed copper (Figure 4), the time-honored metal roof will exhibit some oil canning in 25 or 30 degrees below ambient air. skill of soldering is absolutely central to sat­ direct angles of sunlight. Particularly when As a result, the “delta T” figure used isfactory performance. Even where auto­ pans are new and reflective, these undula­ in movement calculations can ap­ matic seaming is the predominant method tions have often prompted disapproval and proach 250 degrees in cold north­ of installation, soldering may be necessary debate regarding cause.3 The displeased ern climates.6 at features such as concealed gutters, party should be patient, as the eventual which are often problematic in the best of patina will obscure most of the oil canning Structural metal roofs use large, sturdy circumstances. (Figure 2). clips with considerable freedom of move­ Solder follows heat, and pretinning is The initial bright salmon-pink color is ment. Pitched copper roofing, however, usu­ crucial for laps and seams that are to per­ highly reflective but will mature into various ally has smaller, sheet-metal clips. These form in a watertight manner.8 There are four shades of brown as oxides and (later) sul­ may be seamed too tightly, restricting panel distinct steps to be followed when soldering. fides form on the surface. The very desir­ movement. At a minimum, oil canning is They are: able blue-green patina is actually copper likely. In extreme instances, fracturing of 1. Edges that are to be seamed should sulfate, which is the sole corrosion-resis­ seams can result. Breaking the work up be cleaned with an acid agent (flux). tant agent of copper roofing.4 This is an into shorter segments “manages” the cumu­ 2. Using an iron, edges should be

6• INTERFACE F EBRUARY 2009 tinned with a thin coat of solder. be provided when This should be done immediately, using stainless prior to folding or seaming, as the clips to solder oxidizes rapidly. secure copper 3. Once nested onto the adjoining piece panels. (and fastened as appropriate), solder Over its ser­ is then “sweated” into the seam to vice life, copper completely fill it. will eventually be 4. A “third” pass is made with addi­ subjected to some tional solder, perpendicular to the type of concentrat­ seam. This final pass is known as ed loading. Minor “stitching,” and the finished work indentations (such should barely (if at all) telegraph the as from hail) do edge being closed. (Some highly not compromise skilled mechanics maintain that water-shedding stitching is not needed. Indeed, they capability or ser­ argue that any solder flowing into vice-life expectan­ the joint during this step signals cy (Figure 5). A Figure 4 – Especially for low-slope, flat-seamed copper, the time- deviant work during step number 3. number of note­ honored skill of soldering is absolutely central to satisfactory This argument is compelling, but worthy and elabo­ performance. (Photo courtesy of Christopher Waites, ADC the author has not always enjoyed rate copper roofs Engineering, Inc.) association with highly skilled serve admirably in mechanics.) zones having rou­ tine hail exposure. If eventual hail dents will meaning in recent months. The author has Again, the great preference for this work be considered analogous to dents in the been a direct party to dump truck loads of is by iron, not by open-flame torch, which fender of an automobile, an alternative cov­ copper being taken to a landfill. At that time can destroy the flux; it can also destroy ering should be considered.11 (1982), it was not profitable to clean sal­ anything under the metal that happens to Pricing of copper has taken on new vaged metal (remove bituminous contami- be flammable.9 When soldering is rejected (for whatever reason), it may be wise to replace the work rather than to attempt repairs. Adding more heat and solder is not a viable remedy – it will seldom, if ever, res­ cue substandard workmanship. Other aspects are worthy of considera­ tion. Though sometimes omitted, underlay­ ments should be used in most (if not all) copper roofs, especially if panels are installed over wood decks. If self-adhering ice-and-water membrane is to be used, soft­ ening point of the bitumen must be consid­ ered (remember, copper panels can become quite hot during full solar gain). Condensation can sometimes occur, even below open mansard roofs. Some wood treatments (especially fire retardants) can induce corrosion of any metal roof, includ­ ing copper.10 This underscores the need for underlayment. Ventilation of the deck un ­ derside is an appealing attribute of virtual­ ly all pitched roofing. Potential for galvanic action will eventu­ ally be encountered in copper construction, so precautions are advisable. For instance, steel can drain onto copper, but the reverse should be avoided – copper gutters should be used to drain copper roofs. Beyond this, copper rivets should be used (instead of ) when crafting gutter joints and end caps. Physical separation should 3 Lyle D. Hogan, “Distorted Views: Oil-Canning on Metal Roofs Can Be a Common Problem,” Western Roof­ ing, January/February 1996, pp. 71-74. 4 Martin Eastman, “Metal Roofing Offers Wide Variety of Durable Choices,” Roofing Spec, November 1983, page 26. 5 David L. Hunt, “Weathering of Architectural Metals – the Ultimate Dichotomy,” Interface, May 2003, page 30. 6 Rob Haddock, “Metal Roofing from A(luminum) to Z(inc), Part IV, Attachment of Metal Panels,” metal- mag, July/August 2003, page 5. 7 Raymond K. Heisey, “Metal Roof Applications and Details,” February Figure 5 – Minor hail indentations in a copper roof do not compromise water-shedding 2008 seminar in Charlotte, NC, capability (or service life expectancy). If eventual hail dents in copper cladding will be sponsored by Butler Manufacturing considered analogous to dents in the fender of an automobile, an alternative covering Company, Overland Park, KS. should be considered. 8 “Section 14, Specifications,” Copper & Common Sense, Revere Copper Products, Inc., 7th edition, 1982, nants) before its acceptance at a reclama­ As outlined above, copper enjoys good pp. 82-83. tion center. Today, however: architectural appeal. If the unique attri b­ 9 Barry Smith, “Flat-Lock Soldered ut es of this material are recognized, its use Copper Roofing, Traditional Roofing, On three occasions in 2007 (early can bring added value to many projects. Grove City, PA, 2007, page 7. May, July, and early October), With sustainability now being all the rage, 10 Paul Anderson, “Rediscovering the the LME copper price has gone copper holds considerable advantage over Age-Old Beauty of Copper Roofing,” above U.S. $8,000 per tonne several alternative roofing types. If exam­ Roof Design, July/August 1985, before falling back to around U.S. ined under a true life-cycle analysis, copper page 32. $7,000/t. During 2007, the price would emerge the victor in many instances. 11 Lyle D. Hogan, “A Proposal for didn’t surpass the peak level of Uniformly Assessing Hail Damage to U.S. $8,500 per tonne that was Roofs,” Interface, October 2006, pp. touched in May 2006. The copper Footnotes 36-37. price tumbled to a 9-month low of 1 John R. Walker, “Metals We Use,” 12 “Raw Material Price Trends,” Inter ­ U.S. $6,330/t in December 2007, Modern Metalworking, 1968, Page 1­ national Cablemakers Federation, but has been climbing again in 14. www.icf.at/en/6043 January 2008, back to U.S. 2 Design Handbook, Section 1, Fun­ /raw_materials_price_trends.html. $7,280/t. The lowest level damentals: Types of Copper and 13 Anne L. Schade, “Copper in a reached in the last 18 months Properties, Copper Develop ment Sustainable Context,” The Con ­ was in early 2007, when the price Asso ciation Inc., 2008. struction Specifier, November 2007. dropped below U.S. $5,300/t. Even this “low” price is, of course, much higher than the price level that prevailed before copper prices began to rise steeply in Lyle D. Hogan, PE, RRC 2005.12 Lyle Hogan is owner and principal engineer with Fincastle Yet today, most copper manufactured in Engineering, Inc., Swansboro, NC. He is a registered engineer the United States is from scrap (recycled) in six states, a Registered Roof Consultant, a Fellow of RCI, material. Anne Schade reports that a 2006 and an ICC structural masonry inspector. Lyle has designed Copper Development Association (CDA) and administered roofing projects using a variety of systems mar ket study, conducted for a ten-year time across the United States. He is a two-time recipient of RCI’s frame, suggests that at least 70% of the prestigious Richard M. Horowitz Award and chairman of the material used domestically in architectural association’s Interface Peer Review Committee. copper is recycled.13

8• INTERFACE F EBRUARY 2009