Choosing between materials
Copper was chosen for the restoration of Toronto’s Old City Hall in the early 1990s. The original roof was clay-tiled, replaced in the early 1920s with a light-gauge copper to lower the expense associated with maintenance costs. While the light-gauge copper was much different from the clay tiles, the copper application was consistent with the building’s original character, and greatly reduced maintenance costs. The modern restoration continued the historical use of copper, but at a heavier gauge to extend the roof’s longevity.
In order to install the heavier-gauge copper, an additional 13 mm (0.5 in.) of plywood was installed over the existing wood deck to support the heavier weight. Load calculations become an important part of determining the feasibility of using alternative roofing materials on historical buildings.
The high cost of historical restoration makes the longevity of a roof an important factor in choosing new materials. In North America, there are many structures that feature copper that has been in place for over 200 years. In Europe, copper roofs have been in service for more than three or four centuries.
High maintenance costs related to tin roofing, for example, do not make it a wise choice for modern preservation efforts. Tin roofing deteriorates when the coating fades and the iron rusts. Historically, undercoating of tin roofing—which may delay deterioration—was not used, and the surfaces may not have been consistently repainted. The most obvious choices for maintenance-free metal applications are copper and zinc; their value is realized by their longevity.
In addition to the material, it is important to be able to preserve the historical integrity of buildings through the use of similar installation techniques and craft practices (e.g. standing seam, rauten tile, and replacement of dormers and decorative elements). This practice is particularly challenging because the parties have to preserve the history while implementing more contemporary installation techniques. Historical craft practices may be too expensive to follow or have been superseded by modern improvements. In this regard, it is important to find modern craftsmen capable of reproducing historic details.
Cases in point
Two Huntsville, Ala., projects highlight the potential of using zinc and copper in historical roofing rejuvenation. The Episcopal Church of Nativity was built in the Gothic Revival style in 1859. A century and a half later, the church was faced with a deteriorating roof that threatened to damage the historical building. Efforts to determine the original roofing material specified by renowned architect Frank Wills were made, but little or no documentation was found. Additionally, several intervening repairs masked the original materials and the application.
Working within U.S. historical preservation guidelines, which are similar to those in Canada, the church was able to support the installation of a new copper rauten tile roof. Both the choice of metal, and the installation practice, were deemed acceptable alternatives to the suspected original (stamped terne metal) because the modern solution matched as closely as possible the scale, texture, and colouration of the historic roofing material.
The need for new roofing and rainwater systems can be challenging for specifiers working on historical projects. The roof of the Cooper House, one of the very few antebellum structures to survive the U.S. Civil War, was originally terne metal, painted grey—the same application that was popular throughout Canada in the 18th century. To maintain the house’s historical look, the architect chose a proprietary form of pre-weathered zinc for its historically correct grey colour, strength, and durability.
The architect designed a standing-seam roofing system with stainless steel ridge caps, and specified European-style gutter and seamless weld downspout. The historical society governing the site readily approved the application as consistent with the building’s historical architecture.
By carefully weighing the interests of all parties, and by following the decision-making process of Standards and Guidelines for the Conservation of Historic Places, specifiers can be successful in employing new and different roofing materials and applications to historic buildings. The key is to emphasize a compromise between the past and the future by finding a solution that values a structure’s history while ensuring its place in Canada’s cultural landscape for years to come.
Erika Huber has been affiliated with the architectural sheet metal industry since 1993, when her husband, Guenther, a Master Craftsman, founded CopperWorks Corp. (Decatur, Ala.). Currently the CFO of Ornamentals Manufacturing LLC, Huber supports both companies’ efforts to assist stakeholders in the use of architectural sheet metal in the historical restoration and preservation of buildings. She can be reached via e-mail at email@example.com.