Zinc Roofing Applications

The success of zinc roofing can be summed up in a few words: long-lasting, malleable, flexible, aesthetic and prestigious. Because zinc roofing is suitable for all roof pitches above 1:12 and for all types of shapes (straight, curved, folded, etc.), it offers a great deal of freedom of expression for roof design. Further, as with wall panels, product manufacturers provide a variety of choices and options to suit different conditions and design criteria:

• Rolled cap: This traditional longitudinal assembly technique involves timber battens and capping strips. The zinc sheets and long zinc strips are held in place by a zinc batten clip supporting the peripheral upstands. The capping strips are placed into position by overlapping, thus ensuring that the roof is watertight. This style has the key performance advantage of being adaptable to complex shapes and roof penetrations. From a design standpoint, it provides expression of strong, conspicuous contours, shadow effects and urban character. From a construction standpoint, installation is straightforward and easy with the ability for easy dismantling for repair, changes, or end of life deconstruction. This style is suitable for virtually all building types.

Traditional and contemporary zinc roofing applications Photo: VM Zinc, USA

 

• Standing seam: The traditional standing seam system allows long strips of zinc metal to be assembled by forming double folds on the upstands. The sheets of zinc are laid on continuous decking and anchored using stainless steel fixing clips. Ideally suited to large roofing areas, this style of roofing will readily adapt to almost any design with very discreet joins. Since it provides maximum water and wind resistance, it is well suited to areas with harsh climates, strong winds, or heavy rains. This well known technology provides for a fairly easy and cost effective installation and it is possible to optimize metal consumption and minimize waste with the judicious layout of the seams.

• Decorative shingles: In steep roof situations (greater than 25 percent) zinc metal shingles can be used for a more decorative solution. As with shingle installations, the intent is to shed water, not repel it, so consideration should be given to the weather and climate conditions when considering this style.

• Coordination with other building elements: The zinc metal roofing will provide the outer weathering barrier of the roofing system, but obviously coordination with other building components is critically important. Trained and experienced installers are a must as with any roofing installation, but architects and designers should take care to understand the appropriate substrate, insulation, and framing support systems that are suitable for a given design. Product manufacturers have typically developed specific information on these points and even have entire product systems that are designed to work with particular insulation materials, provide a more structural support of their own, or be assembled in smaller panels to allow for greater flexibility. Certain products when placed in contact with zinc can have detrimental effects on the appearance and/or structural integrity of the zinc. There are no issues with zinc in combination with metals other than copper and mild steel. When zinc contacts copper in the presence of an electrolyte (such as water) a galvanic reaction would lead to corrosion of the zinc and subsequent failure of the roof or wall. Run off from a copper surface to a zinc surface must be avoided under all circumstances. Zinc in contact with mild steel is not desirable either, due to similar electron transfers between the metal resulting in zinc corrosion and deterioration.

In general, water should not be allowed to run from a higher potential metal to a metal with a lower one. Install metals in the following order (from top to bottom):

• Aluminum
• Zinc
• Galvanized steel
• Lead
• Copper

Zinc can be installed adjacent to limestone; limestone buildings in Paris have numerous zinc protective flashing located between floors. The run off from limestone onto zinc material is acceptable. However, limestone dust and gypsum dust that are generated during cutting operations can react with zinc in the presence of water and form a superficial coating. The zinc surface must be cleaned of any limestone and gypsum dust. No dust should be in contact with unprotected zinc and good construction practices should be used to limit the amount of dust.

Examples of acceptable contact products for zinc include lead, aluminum (painted, anodized, or bare), galvanized steel, stainless steel and compatible woods including pine, spruce, scotch pine, and poplar. Examples of unacceptable contact products and run off for zinc include but is not limited to copper, steel (non galvanized), gypsum dust/ limestone dust, mortar, rosin paper, bituminous membranes, products with fire retardant and preservation treatments, acidic cleaners, and non-compatible woods including larch, oak, chestnut, red cedar, Douglas fir, white cedar, and all woods with a pH less than 5.

Installed correctly, a building that is clad with zinc wall or roofing panels will have the potential to be a long lasting, durable, attractive, and truly sustainable building over the course of its very long full service life.

University of North Carolina at Greensboro: Building for a 100-year Life Span

As a public institution more than a century old, the University of North Carolina Greensboro has assumed its place among top tier universities in North Carolina. On the longevity of its buildings and their construction, Fred Patrick, Director of Facilities Design and Construction, is very discerning in the selection of materials. He states, "There is, by design, a consistency of colors and materials that contribute to the campus environment. We build our structures for the long term with an eye at a 100-year life. We are in the center of the brick capitol of the United States and that is not lost on our campus. Our exterior wall materials are typically constructed with brick and precast or limestone. Our roofs are built with zinc and slate. Both, with proper installation and monitoring, will meet our design life goals." Each new construction project on the campus is reviewed for total cost of ownership. These costs include first costs, projected and actual maintenance costs, and warranty costs. The State of North Carolina requires that each project be evaluated with a formal lifecycle cost analysis program. Preferred roof construction at the university has gone through a learning process originating with flat roofs that have been problematic with maintenance issues and premature replacement costs. Studies have shown that flat roofs have a typical useful life of only about 17 years and the experience at UNCG is no different. Subsequently, flat roofs have been discarded for a sloped roof design in new construction and modernization. Recent examples of the University's sloped roofing preference can be found in the new Science Building completed in 2003 and, more recently, the Hall for Humanities& Research Administration completed in 2006. Both buildings feature double lock standing seam roofing formed from pre-weathered zinc. It was during the 1997 architectural interview for the Science Building that Andy Zwiacher of Durham, NC-based O'Brien/Atkins Architects first learned of the University's priorities with regard to building materials and roofing in particular. The roof was viewed as a significant part of the design intent to keep within the context of the campus which was moving towards more sloped roof designs. The University also wanted to use materials that would stand the test of time although the selection of such materials is not always an easy decision. Many elements must come together including design, function, color, budgets, the balance of initial costs and long-term costs. "In the case of the University of North Carolina at Greensboro, those priorities came together to construct a building with a zinc roof that should last for a good long time" said Zwiacher. "We continue to specify zinc in the private sector on the right projects." The Hall for Humanities & Research Administration was designed by Calloway Johnston Moore & West of Winston Salem, NC, and completed in April 2006. The firm's Andy Sykes was the project manager. He recalls UNCG's desire to be sure the building had a contemporary feel while still fitting into the context of the campus with its traditional character and pitched roof designs. Once again the life cycle costs were an overriding concern with roofing materials. "Zinc is a very natural material with a self-healing characteristic that protects it from scratches and mars. The color is more natural than other metals which look quite machined and typically do not share the same life span as zinc." The new building provides space for teaching, research, and administrative functions for five of the humanities departments of the College of Arts and Sciences. In addition, space is provided for externally funded research projects and the administration of research at UNCG. Like many universities, the buildings are monitored for performance. While initial construction budgets may come from bonds or grants, many of the University's buildings are self liquidating, which means they must pay for themselves over time. Money is borrowed for construction costs and repaid just as in the private sector. According to Facilities Director Fred Patrick again, "Typically our new construction budgets are ample but our maintenance budgets are scarce. Utilizing better materials that will meet our long-term goals also saves money for us in the long run. The University is willing to pay a little more up front for quality materials that will meet our standards. It is my job to justify these costs to the Board of Trustees. Once they see how products like zinc actually save us money in the long run, we usually get the green light."

University of North Carolina at Greensboro zinc roofing blends in with the context of the campus and meets the life cycle goals of the University. Photo: VM Zinc, USA

 

Peter J. Arsenault, FAIA, NCARB, LEED-AP is an architect and green building consultant based in New York State focused on sustainable design and practice solutions nationwide. He can be reached at www.linkedin.com/in/pjaarch

Umicore Building Products is the world's leading producer of zinc construction products, which have been used successfully for more than 150 years throughout Europe and now for more than a decade in North America. Umicore's line of VM ZINC® panels for roofs and wall systems has been used on a wide range of projects including colleges and universities, museums, airports, libraries and an array of prestigious buildings across the country. www.vmzinc-us.com