Hoffmann Architects Journal of architectural technology published by Hoffmann Architects, specìalists in exterior rehabilitation First lssue 1997 Volume l5 Number I Copper Roofing: An Enduring Linl< Between Past and Future with theìr standard 7}-year warranty, Arthur L. Sanders, AIA Certainly, not all buildings are intended to last more than 30 or 40 years and C rrtor-..ufted copper roofìng, rich may not warrant a copper roof But in detailing, rich in history, speal<s to many are designed for longevity and mer- endurance and long life, its soft blue- it a roof that will endure equally well. green patina a testament to the passage of time, But as a building matedal, Without a doubt, copper was and is a copper shouldn't be relegated to the high initial cost item, typically two or past, despite competition overthe past more times the cost of other roolng few decades from lower-cost, pre-formed types, with the exception of slate and metal roofìng systems and other roofìng tile This high initial cost was a primary types. lf longevity, low maintenance, reason why copper traditionally was and a frong aesthetic statement are a selected only for "important" buildings building owner's goals, copper remains - public facilities, churches, libraries, the hands-down favorite. and other buildings of long-term value to their owners and their communities, When properly designed, detailed, and That cost came from the high level of installed, a copper roof can easily last craftsmansh ip required for instal lation, 50 years or more with relatively little along with the cost of the material itself maintenance or care. And there is Today, modern tools and equipment ample evidence of copper roofs have helped reduce installation costs \ enduring for a century or longer and material waste, Even so, copper as befits the historic, cultural, and- civic installation is still essentially a "f eld job' value of the buildings they so often requiring great skill and craftsmanship grace. For example, the standing seam - and properly detailed design copper roof installed in the I B30s on documents, Philadelphia s Old Christ Church lasted unttl 1967, One remaining section of Overthe long haul, however, a well- the original copper roof on the First designed and correctly installed copper Bank of the United States (also in roof will more than pay for itself One lnstallation of a batten seam copper roof Philadelphia) is still in service today,202 reason forthat is copper's durability, on a New York City high-rise office years later. Stacl< that up against today's which makes it likely to last the life of building. pre-fabricated metal roofì ng systems, the building. Regular maintenance is easrly implemented, as long as design documents and construction have As Senior Architectw¡th Hoffmonn addressed the few special requirements Architects, Arthur L. Sandert A/A oyenees of copper, particularly in planning for mosonry, plozo, ond roofing rehobílitotion thermal expansion and contraction. Þrojects, rncluding mony of the fum's coÞPer rooftng rehobilitotion efforts. ln contraf, today's low-slope membrane Copyright Hoffmann Architects I 997 Hoffmann Architects / Journal roof or steep-slope shingle roof needs Deterioration the runoff from either of these metals regular maintenance, patchìng, and . Copper is susceptible to corrosion will eventually stain the copper darl<- repai¡ and usually requires full replace- from contacl with all<alis, ammonia, brown or blacl<. ment after 25 years. The opportunities some bituminous roof ng cements, . Copper is also subject to erosion from for deterioration are greater with these masonry cleaners, and acidic rainwater rubbing by cables and ropes, abrasion, other roofìng systems, due to the nature (run-offwater in contact with moss, excess handling, foot traffìc, or the of the materials, And that's not to lichen, algae, wood shingles, or airborne constant ddpping of water from above, mention the losses on the aesthetic side, sulfur dioxide) While the copper Coppers distinctive color and appear- patina provides some level of protec- Mechanical failure ance offer design atlributes unmatched tion from acidic moisture, copper roof . Failing to provide adequately for in other roofìng sylems, Whether in a valleys, gutters, and sllylight frames are copper's natural expansion and hìstoric setting or in newer structures, a particularly susceptible to its damaging contraction is the leading cause of copper roof is well wodh restoring or effects. That's because moisture tends mechanical breal<down in sheet copper replacing with the same or comparable to linger in these vulnerable areas, giving roof ng, along with improperly securing custom-crafted design, the acid more time to act on the the roofto the substrate, . copper, Flexure - the bending back and It's All ln The Details . Some early generations of the f re- forth of the copper sheet that occurs A roof is only as good as it's designed retardant chemicals used in dimen- during thermal expansion and contrac- to be, and copper roofìng is no excep- sional lumber and plywood sheathing tion, or through movement caused by tion. Detailing must be exacting, and can also corrode copper, The roof wind - will eventually cause distinc- go beyond industry standard details to should be detailed to minimize tive star-shaped cracl<s in the sheet address specifìc field conditions to opportunities for salt-laden moisture surface, compromising its water- achieve the best result, For copper leaching from the treated wood to tightness. roofìng, it's vital to create details that come in sustained contact with the . An inappropriate or improperly shed, rather than trap, water, The copper, orlo avoid use ofthese prepared substrate can also lead to following section looks at some of woods altogether, roof failure. For example, copper coppers specific problem areas and ways . lron and steel should not be placed sheets installed over cupped wood to avoid these durìng installation or repair. above copper, as the interaction of will eventually tear along the sharp, upturned edges of the sheathing, while the high points of a rough concrete surlace will telegraph through the copper and lead to pinpoint holes in the roof . Secondary causes ofcopper roof failure can include the use of inappro- priate materials, such as using steel nails to secure cleats, The galvanic interac- tion between the steel and the copper will eventually corrode the steel nail and undermine the structural integdty ofthe cleat, Protecting other building materials Copper can hasten the deterioration of other metal buildìng materials through galvanic action, Galvanic action occurs when a vulnerable metal, such as aluminum, zinc, steel, inon, tin, or lead, comes in contact with copper in the A previous attempt to solder over these failed flat seam joints was not successful presence of water. Aluminum and zinc 2 a Volume l5 Number I are the most susceptible to this type of corrosion, Proteclive measures in- clude painting the aluminum, steel, or The ManyVirtues of Copper iron with a bituminous or zinc chro- mate primer, S'n." antiquity, copper has been aprizedbuilding material used for roofìng, flashing, and intricate ornamentation. lt is a highly durable metal The roof should be detailed to prevent which can easily be shaped, stretched, or drawn for use in wiring, or runofffrom copper surfaces from rolled, hammered, or beaten into sheets without cracl<ing or breal<ing, reaching adjacent sur-faces, as traces of Its malleability allows it to be easily folded on-site into waterproof seams copper salts in the run-off can cause to create a weather-tight roofìng surface. Copper is easily soldered, staining of metal, marble, limestone, welded, or brazed, making it a very accommodating material for on-site granite, and bricl<. A properly detailed installation, lt is Íre-resistant, and has passed the Underwriters Labora- ddp edge between 314" and l-112" tory's most rigorous test for wind-resistance, making it an excellent wide can help prevent this, Gasl<eting choice for hurricane- and tornado-prone areas, with sealants, membranes, or other non-absorptive materials is another Another beneflt is the relative ease of care that copper requires overthe isolation technique, years, One reason for that is the distinctive blue-green patina that forms on bright copper over time, creating a tough protective layer which lnstallation Requirements pnevents further interaction with the atmosphere, This protective patina ln most situations, deteriorated copper is created when airborne sulfur dioxide (a product of burning fossil fuels) should be removed and replaced with settles on the bright copper surface and reacts with the metal to create new material, as patching is not usually basic copper sulfate. The patina fìrsl appears as a dull brown and then feasible or reliable, Atlempting to re- gradually changes to blue-green, This weathering process takes only B to solder seams, for example, will serve l0 years to achieve in our highly acidic atmosphere. Lead-coated copper only to aggravate the problem failed of will develop an equally desirable soft gray color overtime, seams, Whether installing a new copper roof or replacing an old one, There are three types of copper: the following recommendations will Soft copper is highly malleable, mal<ing it ideal for decorative uses and help ensure the best performance: intricate ornamentation. lt should never be used for other building . Checl< the substrate: Concrete, construction purposes. stone, bricl<, stucco, and terra cotla can all provide a smooth installation Cold+olled coÞÞer is the most frequently used for roofìng and flashing, surface when properly prepared. offering less malleability than soft copper, but much greater strength. Determine the best seam type based Leod-cooted coÞÞer (cold-rolled coppen coated with lead on both sides) on specifìc conditions: Soldered seams is often used for roofìng and flashing, where the soft grays of the lead provide the best water-tightness, and coating are desired.