Essential Zinc: Building For The Future

Low-maintenance zinc gains popularity for buildings that last
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Sponsored by Umicore Building Products
Janet Zaso

For walls, standing seams - either vertical or horizontal - are popular styles for zinc applications. Often, manufacturers will recommend a single lock versus double lock for the seam because this allows for using a thicker gauge material than typically used for a roof. While a double lock standing seam roof might use a 0.7 mm thick zinc, the single lock standing seam allows for increasing that to 0.8 mm on walls. According to Umicore, design professionals should refer to the manufacturer regarding product thickness for zinc projects because it will vary depending on the panel and sought-after aesthetic.

"[Zinc] can easily be used for flashing details on façades and roofs made from zinc panels and shingles, according to Dean Marchetto. "This allows the designer flexibility to design a façade detail in which the flashing can become part of the designed pattern, all in the same material and color."

Textural walls are another application of zinc that is gaining attention for both interior and exterior walls. Corrugated material is perhaps one of the oldest wall cladding applications, one that has a familiar look in rural and marine settings. Exterior corrugated zinc cladding requires a few extra considerations. First, when panels are laid in a shingled style or separated by a reveal, that reveal must include a drainage system behind it. Reveals can be detailed in a similar fashion to a rainscreen system and mounted on galvanized steel hat channels.

LOW MAINTENANCE MEETS LONGEVITY

An assessment of zinc's potential for a favorable return on investment requires examining more than just material purchase and installation costs. In the case of zinc, these upfront costs are typically higher compared to other choices of material. However, compared to similar metal choices, zinc is priced lower than copper, stainless steel, lead-coated copper and zinc-coated copper. As for installation costs, zinc is comparable to other metals such as stainless steel and copper and is more expensive than painted metal. However, some zinc products, such as pre-formed shingles, cost no more to install than other similar choices. More notable is that zinc is cost effective when the total service life and maintenance costs of the product are considered.

Zinc roofs have been used in Europe since the late 1800s and historical results point towards a high rate of longevity. Today's metal alloy has been standardized and improved and, presumably, is an even more durable product than what was installed years ago in Europe. In the U.S, zinc is newer to the market and less long-term data is available. While the longevity of a properly-installed zinc roof will vary depending on such factors as climate and pollution, a zinc roof can have a service life of 60 to 100 years. Comparatively, an asphalt roof has a life expectancy of 18 to 25 years. For wall applications, the service life is even longer due to less exposure to weathering. In fact, some estimates indicate zinc walls can last
300 years.

University of North Carolina

The sloped roof on the Hall for Humanities & Research Administration at the University of North Carolina in Greensboro features a zinc roof that was chosen for the beauty of the metal as well as expected long life span. New campus construction projects must undergo a formal lifecycle cost analysis prior to approval. For architecture firm Calloway Johnson Moore & West in Winston-Salem, that meant designing a project with a contemporary feel that would fit into the traditional character of the mostly-brick campus andfit within the goal of a 100-year life span.

This is the second zinc roof project the University has undertaken, and like many universities, the buildings are monitored for performance. The school acknowledges that construction budgets tend to be well-funded but maintenance budgets are not, thereby leading to choices that are long-lasting and low maintenance. The self-healing characteristic of zinc and its pleasing natural color were factors in the decision.

Photo courtesy of Umicore Building Products

 

Building professionals should keep in mind that when used in exterior applications, small amounts of zinc are removed from the surface due to weathering from rainfall. The protective patina reforms and the process beings again, however, pollutants in the air will accelerate this process and affect the life span. Replacement of a zinc roof is recommended when 40 percent of the material has been removed.  Measuring this weathering is generally done in microns and can vary from 7 microns a year in a heavy industrial area to 1 or 2 microns a year in a very clean environment. The manufacturer can assist building professionals in estimating the life cycle of a particular application based on climate and pollution.

According to a 2004 U.S. study by Ducker Research Company that sought to measure life cycle costs of three types of roofing systems, metal roofs, including zinc, were found to cost 30 cents per square foot per year whereas asphalt cost 37 cents per square foot per year. Single ply roofs studied were 57 cents per square foot per year. Life cycle costs were determined by adding initial installed costs to annual energy costs and annual maintenance costs, and adjusting figures for inflation.

What factors contributed to the difference in life cycle costs? Owners and property managers reported spending little or no maintenance on their metal roofs. As mentioned earlier, the natural, protective zinc patina allows the metal to heal itself after damage from scratching. This eliminates the need for paints and other coatings. In fact, owners often report needing to do little or no maintenance on zinc. Periodic inspections and seasonal gutter cleaning are among the simple steps owners report taking to maintain their zinc roofs. Maintenance needs will vary and should be discussed with the manufacturer, and as is standard practice for all roofs, owners are advised not to walk on the roof after installation.

Some public institutions are turning to zinc in part for its durability and life cycle cost advantages. At the State University of North Carolina, for example, new campus construction projects must be evaluated using a formal life cycle cost analysis. The requirement led the University of North Carolina to look at building new
structures with a goal of a 100-year-life span. That goal led to two new campus buildings with zinc roofs. Andy Sykes of Calloway Johnson Moore & West, PA in North Carolina was project manager for the Hall for Humanities Research and Administration. "Longevity was reason one," he said about recommending a zinc roof. "Reason two was aesthetics. Zinc worked well because of the appearance, the color was more similar to what historical turn-coated lead roofs looked like and blended with the traditional campus roofs." Sykes also said that zinc's self-healing patina was a factor in the decision.

Zinc's longevity is a factor for architect Bruce Norelius when he considers roofing materials. He said that zinc offers his clients the low maintenance they desire with a longevity that's better than asphalt and other materials.

Two obvious factors in the longevity of a zinc application are the quality of installation and experience of the installer. By working closely with a manufacturer's representative and adhering to guidelines, such as those described herein, building owners and managers can avoid corrosion and other issues that might negatively affect maintenance and longevity.

 

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Originally published in Architectural Record
Originally published in April 2009

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