Copper Roofing: an Enduring Link Between Past and Future
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Volume 15 Number 1 Journal of architectural technology published by Hoffmann Architects, specialists in exterior rehabilitation First Issue 1997 Volume 15 Number 1 Copper Roofing: An Enduring Link Between Past and Future with their standard 20-year warranty. Arthur L. Sanders, AIA Certainly, not all buildings are intended to last more than 30 or 40 years and C ustom-crafted copper roofing, rich may not warrant a copper roof. But in detailing, rich in history, speaks to many are designed for longevity and endurance and long life, its soft blue- merit a roof that will endure equally well. green patina a testament to the passage of time. But as a building material, 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 over the past more times the cost of other roofing few decades from lower-cost, pre-formed types, with the exception of slate and metal roofing systems and other roofing tile. This high initial cost was a primary types. If longevity, low maintenance, reason why copper traditionally was and a strong 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 craftsmanship required for installation, 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 “field 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 1830s on documents. Philadelphia’s Old Christ Church lasted until 1967. One remaining section of Over the 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 Installation of a batten seam copper roof Philadelphia) is still in service today, 202 reason for that is copper’s durability, on a New York City high-rise office years later. Stack that up against today’s which makes it likely to last the life of building. pre-fabricated metal roofing systems, the building. Regular maintenance is easily implemented, as long as design documents and construction have As Senior Architect with Hoffmann addressed the few special requirements Architects, Arthur L. Sanders, AIA oversees of copper, particularly in planning for masonry, plaza, and roofing rehabilitation thermal expansion and contraction. projects, including many of the firm’s copper roofing rehabilitation efforts. In contrast, today’s low-slope membrane 1 Copyright Hoffmann Architects 1997 Hoffmann Architects / Journal roof or steep-slope shingle roof needs Deterioration the runoff from either of these metals regular maintenance, patching, and • Copper is susceptible to corrosion will eventually stain the copper dark- repair, and usually requires full replace- from contact with alkalis, ammonia, brown or black. ment after 25 years. The opportunities some bituminous roofing 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 roofing systems, due to the nature (run-off water in contact with moss, excess handling, foot traffic, or the of the materials. And that’s not to lichen, algae, wood shingles, or airborne constant dripping of water from above. mention the losses on the aesthetic side. sulfur dioxide). While the copper Copper’s distinctive color and appear- patina provides some level of protec- Mechanical failure ance offer design attributes unmatched tion from acidic moisture, copper roof • Failing to provide adequately for in other roofing systems. Whether in a valleys, gutters, and skylight frames are copper’s natural expansion and historic setting or in newer structures, a particularly susceptible to its damaging contraction is the leading cause of copper roof is well worth restoring or effects. That’s because moisture tends mechanical breakdown in sheet copper replacing with the same or comparable to linger in these vulnerable areas, giving roofing, along with improperly securing custom-crafted design. the acid more time to act on the the roof to the substrate. copper. • Flexure — the bending back and It’s All In The Details • Some early generations of the fire- 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 roofing 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 cracks in the sheet address specific 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. roofing, it’s vital to create details that come in sustained contact with the • An inappropriate or improperly shed, rather than trap, water. The copper, or to avoid use of these prepared substrate can also lead to following section looks at some of woods altogether. roof failure. For example, copper copper’s specific problem areas and ways • Iron and steel should not be placed sheets installed over cupped wood will to avoid these during installation or repair. above copper, as the interaction of eventually tear along the sharp, upturned edges of the sheathing, while the high points of a rough concrete surface will telegraph through the copper and lead to pinpoint holes in the roof. • Secondary causes of copper 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 integrity of the cleat. Protecting other building materials Copper can hasten the deterioration of other metal building materials through galvanic action. Galvanic action occurs when a vulnerable metal, such as aluminum, zinc, steel, iron, 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 Volume 15 Number 1 are the most susceptible to this type of corrosion. Protective measures in- clude painting the aluminum, steel, or iron with a bituminous or zinc chro- The Many Virtues of Copper mate primer. Since antiquity, copper has been a prized building material used for roofing, flashing, and intricate ornamentation. It 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 runoff from copper surfaces from rolled, hammered, or beaten into sheets without cracking or breaking. reaching adjacent surfaces, 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 roofing surface. Copper is easily soldered, staining of metal, marble, limestone, welded, or brazed, making it a very accommodating material for on-site granite, and brick. A properly detailed installation. It is fire-resistant, and has passed the Underwriters Labora- drip edge between 3/4" and 1-1/2" tory’s most rigorous test for wind-resistance, making it an excellent wide can help prevent this. Gasketing choice for hurricane- and tornado-prone areas. with sealants, membranes, or other non-absorptive materials is another Another benefit is the relative ease of care that copper requires over the 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 Installation Requirements prevents further interaction with the atmosphere. This protective patina In 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 first appears as a dull brown and then feasible or reliable. Attempting to re- gradually changes to blue-green. This weathering process takes only 8 to solder seams, for example, will serve 10 years to achieve in our highly acidic atmosphere. Lead-coated copper only to aggravate the problem of failed will develop an equally desirable soft gray color over time. 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, making it ideal for decorative uses and help ensure the best performance: intricate ornamentation. It should never be used for other building • Check the substrate: Concrete, construction purposes. stone, brick, stucco, and terra cotta can all provide a smooth installation Cold-rolled copper is the most frequently used for roofing and flashing, surface when properly prepared. offering less malleability than soft copper, but much greater strength. • Determine the best seam type based Lead-coated copper (cold-rolled copper coated with lead on both sides) on specific conditions: Soldered seams is often used for roofing and flashing, where the soft grays of the lead provide the best water-tightness, and coating are desired.