The team selected copper for the restoration work, despite the fact it was not the original material used during either buildings’ original construction. Copper was recommended for the complete roof replacement due to its noble qualities, esthetic appearance, and its use of traditional material at the time when both structures were erected.
Although the upfront cost of the material was higher, it was deemed the best choice in the long run. Generally, any higher initial costs for copper applications typically are offset by low- to no maintenance costs over the operational life of the building. When properly designed and installed, a copper roof provides an economical, long-term solution. Its low life cycle costs are attributable to the low-maintenance, long life, and salvage value. Unlike many other metal roofing materials, copper requires no painting or finishing.
The overall multi-roof project encompassed many different copper roofing types, including a batten-seam assembly on the Currie Building, interlocking small pan on the Mackenzie Building, as well as standing-seam, soldered flat-seam, and barrel roofs. The heritage consultant designed a unique system of interlocking flat-seam small pans in order to improve both the esthetic and performance of the mansard roofs on the Mackenzie Building. The pans that were in place before the restoration were oddly sized and not esthetically pleasing. The newly designed and installed small pans on the mansard hips resolved in hip rolls—a reintroduced detail from the original construction. The team also replaced an unsightly roof-level stucco addition with seamed small copper pans to blend in with the historical mansard.
Additional restoration work on the Mackenzie Building included the replacement of all cornices, acanthus leaves, dormer cladding, and ornamentation. One of the most concerning problems was with the cornice gutters. The integration had been failing, causing decay in the roof structure and leakage into other metal and woodwork on the roof. The restoration team re-designed the gutters for proper function while allowing for thermal expansion. Further, the acanthus leaves needed to be reconstructed as they were deteriorating due to snow and rain accumulation, as well as from the nesting, munching, and burrowing from small animals. In an effort to provide the owner with a low-maintenance, but visually authentic, appearance on the extensive ornamental cornice work, the team used zinc-tin coated copper in place of painted lead or copper work. The former was also used for the individual-formed acanthus leaves.
The copper detailing on both buildings was carefully studied, replicated where appropriate, and improved at locations where issues of expansion or failure were apparent. The team expects the new copper roofing systems to last approximately 80 to 85 years. However, since the team left the new roofing system to age naturally, it will change dramatically over its lifetime. The bright copper penny appearance of the roofing systems will develop into a striking green patina over the decades.
Copper and its principal architectural alloys are relatively active metals, which tend to oxidize when left unprotected. Long-term atmospheric exposure in non-arid climates generally results in the formation of the naturally protective grey-green patina. The natural weathering of copper to the characteristic blue-green or grey-green patina is a direct consequence of the mild corrosive attack of airborne sulphur compounds. In the atmosphere, these compounds combine with water vapour to form dilute oxidizing acids, which react with copper surfaces. Since the Currie and Mackenzie Buildings are in a costal environment, these changes will likely occur in five to seven years. Copper usually weathers to a uniform russet brown within six to 12 months of initial exposure to the atmosphere, except in arid climates.
Although the roofing system may need to be replaced before 100 years—this might not be the case, since many copper roofs in Canada are well over a century old—the actual metal can be used time and again. Copper is one of the most sustainable building products, as it can be reused without any loss of its original properties. It is one of the most thoroughly recycled, structural, and architectural metals. Nearly half of copper used today has been used in the past. One reason for copper’s high recyclability is its durability. Unlike other metals, it corrodes exceedingly slow in natural environments. After the protective patina forms, corrosion drops to little more than a few millionths of an inch per year.
The extensive copper restoration work and attention to detail earned the Currie and Mackenzie Buildings a 2016 North American Copper in Architecture Award (NACIA) from the Canadian Copper and Brass Association (CCBDA) and the Copper Development Association (CDA). Historically, copper has long been used because of its great natural beauty and finish, performance and durability, long service life, and recyclability. Today, it is adapted and utilized for a wide variety of contemporary and cutting-edge applications. It is these characteristics that make it attractive for new construction as well as historic restoration projects throughout North America.
In the case of the RMC project, copper’s superior performance and longevity made it the obvious choice as the replacement material. Its appearance can complement any style of building, from the traditional to the modern. When properly designed and installed, a copper roof provides an economical, long-term roofing solution.
Stephen Knapp is the program manager of the Sheet, Strip, and Plate Council for the Copper Development Association (CDA), and executive director of the Canadian Copper and Brass Development Association (CCBDA), the national trade association in Canada for the copper industry. Knapp is also involved with guiding the market development and promotional efforts for a wide variety of copper and copper alloys applications, such as tube and plumbing, electrical, renewable energy systems, and energy-efficiency technologies. He can be reached via e-mail at email@example.com.