by Katie Daniel | November 25, 2015 12:24 pm
By Stephen Knapp and Larry Peters
Structures across Canada are turning green in more ways than one. The Beaty Lundin Visitor Centre (Britannia Beach, B.C.), the University of Toronto at Mississauga Campus Instructional Centre, and Oshawa’s University of Ontario Institute of Technology (UOIT) are examples of buildings clad in copper—a material that naturally turns green, and is 100 per cent recyclable as it can be used over and over without losing its engineering properties.
Trends have shown ‘green’ building is percolating in the minds of architects and contractors across Canada. There has been an increase in the number of Leadership in Energy & Environmental Design (LEED)-certified buildings in the country and a surge in copper cladding submissions for the North American Copper in Architecture (NACIA) awards program.
Sustainability is not copper’s only asset. The metal is also durable, flexible, malleable, lightweight, fire-resistant, corrosion-resistant, and available in an array of finishes and colours. These attributes have given building professionals the opportunity to expand their creativity and go beyond the limits of traditional wall cladding materials.
Typically, when left unprotected, copper and its principal architectural alloys naturally oxidize. This causes the metal to change in hue from the natural salmon pink colour through a series of russet brown shades to light and dark chocolate browns. From there, it will develop a dark, dull slate grey or dull black from which the blue-green or grey-green patinas emerge.
The Beaty Lundin Visitor Centre, a 2011 NACIA award winner, has developed a very site-specific blue-green patina due to the microclimate around its Pacific West Coast location and the choice of prepatinated copper cladding. The high humidity has caused the panels to vary in colour daily and create a lively and active response to the oceanside settings. In industrial and seacoast atmospheres, the natural patina generally forms in as little as seven to 10 years.
The protective chemical reaction occurs when a corrosive attack of airborne sulphur compounds leads to a gradual change in the surface colour until equilibrium is reached and the change is stabilized. When the quantity of airborne sulphur dioxide is relatively low, patina formation may not reach a dominate state for 10 to 15 years. In arid environments, the basic sulphate patina may never form due to the lack of sufficient moisture to carry the chemical conversion process to completion. To achieve the mature blue-green hue at the initial phase of a project’s life, architects can opt for prepatinated copper.
The University of Toronto Mississauga Instruction Centre, a 2012 NACIA award-winner, displays a prepatinated finish that is highly responsive to conditions of light and humidity. As a result, the building presents subtle variations in colour and texture from day to day and hour to hour. The same copper was also installed in the interior of the facility. To secure the desired colour, a clear, matt, acrylic sealer was applied, preventing direct human contact with the patina.
Achieving desired esthetics does not require sealers or paints. A wide variety of copper alloys are available for architectural use, including commercial bronze, red brass, cartridge brass, muntz metal, architectural bronze, silicon bronze, and nickel sliver. Technically, alloys composed primarily of copper and tin are considered bronzes, and those composed chiefly of copper and zinc are brasses. Copper, brass, and bronze are ideally suited for wall cladding applications. These materials are strong, lightweight, malleable, highly corrosion-resistant, and available in numerous factory-applied alloys to achieve unique finishes and colours.
When considering copper system, designers should reference ASTM B370, Standard Specification for Copper Sheet and Strip for Building Construction, which defines composition, dimensional tolerances, and mechanical properties of acceptable building material. The most popular temper designations for sheet copper used in wall cladding systems are ‘H00’ or ‘H01’ (i.e.‘Cold Rolled’ or ‘1/8 to 1/4 Hard’) as well as ‘H02’ (i.e. ‘1/2 Hard’). With its many attributes, this family of metals can be the solution to many innovative building designs—especially those seeking to accentuate the natural environment.
The aforementioned Beaty Lundin Centre is clad in a combination of dark-stained horizontal wood cladding and prepatinated copper panels (75 per cent recycled content). The design team deliberately chose materials and forms that respond to the many elements onsite.
Wood is carried through the building and overall site in different guises. The rectilinear prepatinated copper panels of the visitor centre speak to the modernity of the historic Concentrator Building—a wonder of technology when originally built. The footprint of the new visitor centre was expanded to embrace the neighbouring buildings and structures, creating intimate interstitial spaces to juxtapose old and new.
The UOIT building, another 2012 award-winner, also had a sustainability goal—to create a campus that limited energy and resource consumption while providing a supportive and inspiring environment for students. It took great effort to create an organization of compact and efficient buildings integrated into a coherent vision of the campus.
The building encloses the primary space of the campus, including a formal landscaped quadrangle and an informal park space. These elements are interconnected with the landscaped routes and covered colonnades between the buildings. The organization of the buildings on campus was devised to preserve site area and promote an urban setting for students, while also establishing a sustainable connection to the Oshawa Creek Ravine. In accordance with ‘going green,’ the university meets the LEED Gold requirements of environmental design, and the lifespan of copper ensures a long service life consistent and supportive of this goal.
To achieve the desired look, both flat seam and standing seam detailing was utilized within the rainscreen cladding and soffit systems. The cladding is typically mounted off of concrete masonry units (CMUs), with an assembly of galvanized adjustable Z-grits and perforated acoustic deck to accommodate ventilation within the wall assembly.
Flat and standing seam cladding systems are two of the most popular types of installation, both of which were used to clad the UOIT and the Beaty Lundin Visitor Centre, and can be grouped into the ‘traditional’ category, as opposed to the ‘engineered’ category.
Traditional systems typically make use of relatively thin sheet copper panels attached to a solid, smooth, nailable substrate. On the other hand, engineered systems vary in appearance and capability from smooth, flat systems of thick copper to composite copper clad material. They also include deeply brake-formed and textured systems to perforated copper panels allowing diffused light to reach inhabited areas. Two of the most popular engineered systems are curtain wall and copper screen panels. Flat, circular, and uniquely shaped walls can easily be covered with copper because of the different cladding assemblies available.
This type of siding is usually fabricated from 680-g (24-oz) copper. Its profile is designed to provide very tight joints between panels, and results in an extremely flat wall appearance with minimal shadows. Panel depth is approximately 6 mm (1/4 in.). This system is self-flashed at horizontal seams using a double-fold detail.
The panels are installed from the top down. The bottoms of the panels are fastened to the substrate with screws through slotted holes in the siding. The screws are not fully tightened to allow the siding to expand and contract.
Transverse seams are lap joints with a minimum of 152-mm (6-in.) lap. The seams should be staggered on successive runs to prevent buildup of copper material. Lock strips and flashing are of the same weight as the siding.
Profiled copper panels can have a variety of shapes and sizes. They can be formed onsite with a brake or powered forming equipment, or they can be pre-manufactured and specified with embossed patterns or other designs.
The minimum recommended weight for copper used on profiled panels is 453 g (16 oz), but some panel profiles may require heavier material. Support blocking behind the panels may be required depending on panel thickness and dimension, along with the wall configuration (i.e. straight or curved). A continuous nailable substrate is used with profiled panels. Cleats screwed or nailed to the substrate are used as a fastening method.
This type of siding is typically fabricated with 3-mm (1/8-in.) thick muntz metal spandrel panels at each floor slab. The result is a uniform colour among the exterior materials. These details demonstrate the approach used to construct a copper alloy curtain wall in a historically significant building. Modern construction methods and materials would certainly improve the moisture and thermal control of the exterior skin. This system supports itself from floor slab to floor slab—meaning no substrate is required. However, steel brackets are used at every slab as a fastening method.
Copper screen panels are part of a manufacturer’s engineered system. The details illustrate the main concepts in the design of copper screen panels. The system uses metal support brackets and channel tracks to carry the copper panels. The support brackets can be attached to virtually any kind of building structure.
The copper screen panels act as a lightweight finish screen. The system is designed to be a water-shedding rainscreen. Alternatively, the panels can be perforated or have shaped openings acting as sun or decorative screens. The backup wall system should always be designed to be watertight.
Isolator clips are used between the metal support system and the copper panels to separate dissimilar metals. The minimum gauge of the copper panels is dependent on the size of the panels and the design of the specific system used. The manufacturer’s recommendations should be followed. Any substrate or structure is specified by the system manufacturer. The fastening method typically specifies screws or bolts, but is ultimately determined by the system manufacturer.
‘Going green’ is not just a trend. With an increased demand on natural resources, numerous design/construction professionals and building owners are realizing the importance of sustainable principles. Copper and its many alloys offer esthetically stunning qualities along with unique physical and mechanical properties. This ensures designers and building owners not only achieve their visual aspirations and performance specifications, but also meet their environmental and cost-performance goals. While no one can exactly predict what the building and construction market will do in the future, it is evident copper will remain an important building material for years to come.
Stephen Knapp is the program manager of the Sheet, Strip, and Plate Council for the Copper Development Association (CDA), and the executive director of the Canadian Copper & Brass Development Association (CCBDA), the national trade association in Canada for the copper industry. He is also involved with guiding the market development and promotional efforts for a wide variety of copper and copper alloys applications—tube and plumbing, electrical, renewable energy systems, energy-efficiency technologies. Knapp can be reached via e-mail at email@example.com.
Larry Peters is project manager for CDA. His responsibilities include providing training and technical assistance to architects, interior designers, contractors, engineers, and others interested in copper and copper alloy material for building construction. A 1987 graduate of West Point, Peters has spent almost two decades working exclusively with architectural metals. He travels extensively for the CDA—educating the industry on benefits and proper uses of copper in construction. Peters can be reached at firstname.lastname@example.org.
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