Zinc Roofing and Wall Systems  

Architects have a number of choices when selecting architectural metal for roofing or siding based on the variety of design conditions in different building types. Many of those choices are rather energy intensive such as aluminum, copper, painted steel and stainless steel. However, zinc is emerging as an architectural metal of choice in the U.S. due in part to its comparatively low level of energy intensity and its widespread and long-term use in other parts of the world. Design professionals in European cities such as Paris, have specified zinc roofs since the late 1800s where the distinctive gray patina continues to crown over 80 percent of the rooftops there—some of which have been around for more than 100 years. Zinc building products, including roofing, wall cladding and rainwater systems, are thus enjoying new popularity in the U.S. due to recognition of its sustainability qualities and its long-lasting, low-maintenance benefits for owners.

Properties of Zinc

Zinc is a naturally occurring element (Zn is #30 on the periodic table) and a significant mineral that is prevalent throughout the world. In fact, it is reported to be the 23rd most abundant element in the earth's crust found not only in rocks, soil, air and water, but also in all living organisms including plants, animals and humans. Zinc is mined worldwide predominantly from extraction processes that avoid strip mining meaning that less land is disturbed and any potential environmental damage is minimized. Various projections have been made about the worldwide supply of zinc, but current estimates predict up to 750 years' worth of supply at current extraction levels. When recycling and reuse of zinc is considered, the projections are even longer.

Photo courtesy of VM Zinc Office building, Hoboken (Belgium) Designed by Sylvie Bruyninckx, Conix Architects

When zinc is used as a building material, it is actually fabricated as an alloy. Typically, it is 99.995 percent pure zinc, produced by an electrolytic process that introduces very controlled trace quantities of copper and titanium. The copper helps with mechanical resistance, making zinc easier to work with. The titanium is added to alleviate the tendency of material creep. Historically, it was observed that a sloped pure zinc roof on a building would become much thicker at the bottom of the roof than at the top in as little as five years. The zinc would literally “creep” down the roof over time, prompting the addition of titanium to overcome that problem.

The manufacturing of zinc into building products has been refined over the past 100 years or more to the point where it is quite efficiently and sustainably done. Once the metals are mined, they go through a casting process at a mill that obviously requires heat to form the metal into usable portions for processing. The environmental air emissions produced from zinc processing at these plants are minimized due in part to the use of up-to-date equipment and emission abatement processes. But compared to other metals, it is worth noting that zinc requires significantly less energy to process due to its relatively lower melting point of 786 °F compared to other metals like aluminum at 1,120 °F, copper at 1,983 °F, and steel at 2,372 °F. Following this process, the zinc is then rolled, cooled and transformed into large primary coils which are further rolled and cut into smaller, saleable coils to be formed into specific building products.

Photo courtesy of VM Zinc Zinc forms a natural gray protective patina and can be pre-weathered in a variety of colors.

ASTM B6-09 is the “Standard Specification for Zinc” as a metal and covers zinc processing from ore by a process of distillation or by electrolysis in five grades: LME grade (related to the London Metal Exchange standards), special high grade, high grade, intermediate grade, and prime western grade. Under this standard, the zinc metal is tested to conform to chemical composition requirements free of any surface corrosion and adhering foreign matter. The most common, but separate building-related standard for products then manufactured out of zinc metal is ASTM B69-09 “Standard Specification for Rolled Zinc.” This standard covers Type I coils or sheets cut from strip rolled zinc, and Type II zinc plates such as boiler and hull plates produced by any rolling method. This accepted standard dictates the dimensional tolerances for thickness, width, length, saber and flatness. It also dictates the quantity of the trace elements that can be contained in the product.

While two-thirds of the zinc manufactured worldwide is used for flashings and rainwater goods, zinc roofing and wall cladding have become attention grabbing design elements. Products are available in a full range of applications from low-sloped roofing, high-sloped decorative roofing, ornamental features such as eyebrows and dormers, wall panels, rain screens, and sun shading devices. As an exposed and visible part of the building envelope, it is distinguished by its beautiful patina characteristics that many building professionals are starting to understand and seek. When rolled zinc first comes out of the mill, it is shiny like mill-bright aluminum. As the material is exposed to air, humidity, and pollution, it weathers, naturally creating a gray-colored patina that develops over time, much the same way bright mill copper develops a brown and then green patina over time. With zinc, this natural patina is a layer of zinc hydroxy-carbonate that typically takes 2 to 5 years to develop fully depending on environmental factors such as air quality and humidity. So, in areas with a higher concentration of CO2, the patina appears more quickly while zinc used in protected interior applications may rarely, if ever, develop a patina. Once the patina develops, the zinc has a uniform and consistent color of gray for its lifespan. However, the patina layer also has unique characteristics that contribute to its sustainability. The patina layer is compact and insoluble to rainwater which thereafter controls the rate of corrosion. This patina is said to be a self-healing protection for the zinc. If it becomes scratched or is removed mechanically, it will naturally redevelop from continued exposure to rainwater and carbon dioxide. The scratch would appear first as a shiny area but would then appear to actually “heal” itself as the patina reforms.

Zinc manufacturers also offer pre-patina materials, sometimes called pre-weathered, with a gray look that is very true to the natural soft gray patina. To achieve this look, the shiny or natural zinc coils are run through an acidic bath giving the material a weathered appearance. The longer the period of time they are in the bath, the darker the resulting color. Manufacturers also offer factory-applied transparent organic coatings that include subtle blues, reds and greens. Over time these colored and darker shaded materials will still develop the natural gray zinc patina eventually. The length of time for this to happen, however, still varies with air quality but typically these colors will last up to 30 years before gradually changing to the natural gray.

Photo courtesy of VM Zinc Zinc metal is produced into rolls with an initial shiny bright appearance.

Many manufacturers work with building professionals during the design phase and even during construction to advise on installation, and many strongly recommend or even require training prior to installation. In the process, a misperception that zinc is hard to work with and install is being overcome. One aspect of working with zinc, similar to all architectural metals, is its expansion and contraction. Zinc will move approximately 1 inch in 30 feet so the design must be engineered to accommodate this normal thermal movement. To achieve this, a combination of sliding and fixed clips must be installed in zinc roofing while wall systems use similar measures to achieve the same results. The sliding clips consist of two parts in which one part can slide to accommodate thermal movement. Working temperature is another misunderstood aspect of working with zinc and is particularly important when bending the material on site. The material is malleable but can become cold and brittle at lower temperatures. Therefore, zinc should not be folded when the metal is at temperatures of less than 45 °F. Crazing, which is seen as long wrinkles in the material, can occur if this is attempted. When working in temperatures below 45 °F, installers can use a heat gun to warm the material to the right temperature for bending and installation or fold the material in a temperature-controlled environment before moving to the building site for installation. Pre-manufactured wall panels and flashings also limit the need for bending zinc on the job site. It is important to factor temperature into construction scheduling when planning to bend or fold the material prior to installation. Once the material is installed correctly, however, low temperatures do not create problems provided accommodations have been made for thermal expansion and contraction.

In addition to the strong historical track record of zinc, architects should also be aware that there are some emerging trends and practices of companies that manufacture zinc building products that will make it easier to specify and design zinc into buildings in the U.S. First is the offering of material in 48-inch-wide products instead of only the previously available meter-wide material. This coordination with American standard construction sizes will make it easier to design and install zinc wall and roofing products at new scales and with more economical installation. Second, is a global approach to the fabrication and service for a specific product. This means that a product can be specified in the U.S. for a project in Europe, China or the Middle East and have exactly the same make up and characteristics in any of those locations. Finally, zinc is being used innovatively to improve building performance such as rain screen products that harness air flow in parts of the building envelope for enhanced heating, cooling and ventilation. Coupling all of this with a growing awareness of an envelope that meets a strong and positive life-cycle cost analysis, architects and designers are becoming increasingly savvy in making long-term choices that allow for both contemporary and traditional aesthetics, even allowing a seamless flow from roofing to walls in some cases.

Building and Sustainability Using Zinc

Zinc has emerged as a particularly pertinent choice for the construction of buildings that respect the environment. Apart from its natural and life essential aspect, rolled zinc is remarkable for its durability, its excellent recyclability and the moderate amount of energy required for its production. Further, some manufacturers offer solutions that meet sustainable building requirements by integrating solar collectors, enabling external insulation, keeping thermal bridges to a minimum or improving acoustics. These characteristics are supplemented by the long term sustainability of zinc products including a life expectancy of more than 100 years, little or no maintenance over the life-time of the product and even no replacement required over the life-time of building. To be a bit more specific, the following green building traits have been identified by the International Zinc Association and several manufacturers:

Life Cycle Analysis

Photo courtesy of VM Zinc The sustainable qualities of zinc exemplify how its use respects the environment.

Life Cycle Analysis (LCA) is a standardized tool used to assess the environmental characteristics of building products. An LCA starts with an inventory of natural resource consumption (mining and energy resources), substance emissions (into the air, water, soil) and waste produced at each stage of the product's life cycle. The second step consists of assessing the environmental impacts associated with these flows. LCA has received more attention in recent years, particularly during the process of developing the soon to be released International Green Construction Code (IGCC). Among the provisions of this emerging addition to the family of codes, Material Resource Conservation and Efficiency is a key piece which calls for a Building Service Life Plan to be included in the construction documents for the project. Of particular note is the identification of 100-year and 200-year service life elements. The long life expectancy of zinc and the ability to readily perform a LCA will readily support this requirement.

Separate from requirements of codes and standards, many clients look for very positive LCA study results for building material and product choices as well. Toward that end, the International Zinc Institute has used LCA as a standardized scientific method for systematic analysis of all mass and energy flows as well as environmental impacts attributed to a product system, from raw materials acquisition to end-of-life management. The terms “cradle to grave,” “cradle to cradle” and “total cost of ownership” describe this overall full life cycle concept of materials. Reviews of LCA studies are not only a matter of simple longevity, but also of the costs necessary in maintaining a material throughout its service life. To take zinc roofs as an example, a 2004 study conducted by Ducker International documented owners and property managers reporting little or no maintenance on their metal roofs (to be fair, the study included all types of metal roofs, not just zinc). Hence, metal roofs, including zinc, were found to have a Life Cycle cost of only 30 cents per square foot per year whereas asphalt cost 37 cents per square foot and single ply roofs cost 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 over the course of ten years, and adjusting for inflation. A comparison of maintenance costs to initial costs over the life of the roof showed that owners of metal roofs spent approximately 3 percent of total installed costs on maintenance, versus 28 percent for asphalt and 10 percent for single-ply membranes. More specific studies comparing zinc roofing to other long lasting roofing materials have shown that, when including a credit for recycling of material at the end of its useful life, zinc has a noticeably smaller environmental footprint and a more favorable life cycle result than aluminum, copper, stainless steel, or tiles.

Photo courtesy of VM Zinc 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.

Reducing Embodied Energy in Materials

Zinc production is friendlier to the environment than other metals through its comparatively low embodied energy. Embodied energy includes the total amount of non-renewable energy needed to create one unit of a finished product, including raw material extraction, transport, manufacturing, assembly and installation. Among the non-ferrous metals used in building, zinc has the lowest embodied energy. It is the least energy intensive to produce, requiring one fourth the energy of aluminum, and one third that of copper or stainless steel. Zinc is less energy intensive to extract than many other metals, and requires lower heat and therefore less energy to process. A complete embodied energy balance sheet must also take into account the energy value of labor to repair or remove old systems such as asphalt roofs, the energy cost of the replacement materials, the energy used in transportation of materials on each occasion, and impacts at landfills. Use of a longer lasting material such as zinc eliminates the cost and embodied energy of such removal or repairs of other roofing systems with shorter service lives. By contrast, at the end of the service life of zinc, an estimated 95 percent of the energy content embodied in a zinc product is conserved during recycling meaning that significantly less energy is used to produce zinc building products when recycled material is used instead of mining and processing new ore.

Photo courtesy of VM Zinc, USA https://www.vmzinc-us.com/Sustainability.aspx Embodied energy in different types of architectural metals

Recyclability

Very few common building materials, including those considered to have low embodied energy, can match the recyclability of zinc material. Architectural-grade zinc must be very pure, and so it contains higher percentages of pure ore than industrial-grade zinc. However, once the pure architectural alloy has been created, it can be recovered and reprocessed for use in new architectural products. Zinc is 100 percent recyclable and in Europe 95 percent is recovered during demolition or renovation work. Used rolled zinc is re-used in different applications including brass production and foundries. With this exceptional level of recycling, in environmental terms, rolled zinc is one of the most efficient materials among the metallic solutions used for building envelopes.

Durability

Since zinc is a non-ferrous metal, it is not subject to the rust and corrosion found in iron, steel, and other ferrous materials. According to the International Zinc Association's “Zinc for Life” program, “Zinc material requires little maintenance over its service life; its (natural) patina constantly renews itself as it weathers and ages and will 'heal over' scratches and imperfections, requiring no touch-up or repainting. Because the metal is uncoated, there is no possibility of the fading, chipping or peeling that otherwise needs recurrent attention. A single zinc roof, with a lifespan of 80 to 100 years may well outlast the building it has been sheltering.” It should be noted that wall panels using zinc, without the environmental rigors of roofing applications, may have service lives of 200 to 300 years, depending on the product used and local conditions. Of course, 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, building owners and managers can avoid corrosion and other issues that might negatively affect maintenance and longevity.

Ability to Recover and Recycle at End of Useful Life

Removal and disposal of typical building materials can be a complex and costly job, and the resulting debris may have low or no value ending up in a landfill producing the associated costs for freight and disposal plus the long-term cost to the environment. However, of the millions of tons of discarded building materials taken to landfills every year, there is hardly a scrap of architectural zinc. This is because metallic zinc can be recycled indefinitely without loss of its chemical or physical properties. This theoretically infinite recyclability is, in fact, being approached in reality in the case of zinc used in buildings. The overall recycling rate for architectural zinc recovered from renovations and removal from old building is over 90 percent in some countries because of its high value. In Europe, buildings whose zinc parts outlasted them are numerous yet virtually no zinc on a building ever goes to a landfill. Recycling of zinc is a well-established industry because products can be recovered easily at the end of their life and there is an extensive network of buyers offering advantageous prices.

Photo courtesy of VM Zinc, USA https://www.vmzinc-us.com/Sustainability.aspx The ability to recycle and re-use zinc at the end of the service life of a building.

Reducing Construction Waste

The standardization of sizes of zinc products means that less cutting and scrap material may be produced during any given project. Nonetheless, any zinc construction wastes can easily be separated from other metals and sent to any local metal scrap dealer. In the United States, zinc is commonly reused by the galvanization industry or may be fabricated into other products such as paints and sunscreen. Even small amounts of scrap zinc generated on jobs are valuable and readily sold.

Selecting Low-Emitting or No-Emitting Materials

Part of the beauty of zinc metal comes from its natural coloration which means that no additional paints, sprays, or other treatment is needed. As a result, manufacturers, fabricators, installers, and users will never need to apply any other coatings on the metal. Consequently, no Volatile Organic Compounds (VOCs) ever need to be introduced that might generate emissions which are contrary to healthy indoor environmental quality.

Innovation in Applications

Because of the versatility and wide range of possible building applications of zinc, it is possible to be very creative in its use to achieve sustainable building designs. Some of these innovations can take the form of advanced building envelope solutions such as rain screen designs, roofing variations, sun screens, etc. Zinc based batteries and fuel cells can be a contributing portion of an onsite renewable energy solution for buildings. Architects looking for advancing the state of green building design through innovation will find plenty of opportunity to pursue creative solutions when considering zinc for those solutions.

With all of these sustainability and durability qualities, zinc has become commonly used as a stand-alone metal product or in combination with other metals for a variety of uses that most designers are probably already familiar with. This includes mixing zinc with copper to form brass or using it to galvanize steel based on a chemical reaction that protects the steel from rust and corrosion. Zinc is also used in batteries and recently in fuel cells for alternative energy solutions. Metal flashings and roof accessories including historical building ornaments (such as metal finials, vanes, campaniles, dormers, etc.) can all be fabricated from zinc as an alternative to copper and other less sustainable metals. Similarly, rainwater collection gutters and downspouts made from zinc are a popular non corroding alternative to other metals. Finally, when formed into rolls and sheets zinc is ideal for fabrication into roof panel systems and interior and exterior wall panel products.

Zinc Roofing Applications

Photo courtesy of VM Zinc The ability to use zinc on low sloped and steep sloped applications makes it suitable for a variety of building forms.

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. It is important however, to address zinc corrosion properly which can be impacted by environmental conditions such as salt spray, acid rain and construction or masonry dust. Generally, one of three approaches is used to prevent zinc corrosion from moisture. Skip sheathing is the oldest method and involves placing pine boards beneath the zinc roofing. The boards are spaced apart so that when condensation on the back side of the metal forms and drips off, it will drip behind the pine boards where it can dry from air flow behind it. This approach is still followed in Europe in some places and contributes to the longevity of some European buildings. A newer approach calls for installing a drainage mat beneath the zinc roofing. And the latest protection approach is a special backside polymer coating. These coatings range from 30 to 60 microns thick and protect the zinc metal from coming into contact with moisture from condensation. The first generation of coatings was white in color, but today gray coatings can be found to aesthetically match the natural patina color of zinc.

What about protecting zinc from corrosion due to salt spray? Sea salt can alter the chemical patina process and result in a lighter or streaked color. Therefore, in seaside locations, zinc products may need regular rinsing with fresh water.

Based on all of these roofing properties, manufacturers offer a variety of choices and options to suit different conditions and design criteria:

Batten Seams

Batten seam roofs are one roofing style option that is suitable for virtually all building types, particularly complex shapes. Experienced installers only need simple tools for the work which involves fastening a strip or bar to the structural deck and then attaching the zinc roofing panels to it. The zinc sheets 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. When working with zinc in this manner, if the batten cap is to be bent downward, the legs of the cap must be bent at an angle less than 90 degrees. The angle is important to accommodate for thermal expansion and contraction. A straight 90 degrees could not allow enough play for this movement. The proper leg angle is a common mistake made by inexperienced installers. In some cases the leg is not bent down at all, but is simply capped off.

Standing Seam

Zinc roofing is also very suitable for standing seam applications. In a standing seam roof, the long seams on adjacent zinc panels are bent up, overlapped or folded to create the weathering surface. Note that the seam is fabricated in a manner to allow for the expansion and contraction of the material. The height of the seam is typically one inch however heights up to one-and-a-half inches are common for snowy areas or low slope roofing applications. This traditional standing seam system allows long strips of zinc panels to be assembled over a sizable area. 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.

Given the design flexibility, aesthetic diversity, and sustainable durability of zinc roofing, it is easy to see why it has become a material of choice for metal roofing, particularly on green buildings. For similar reasons, the use of zinc for wall systems is on the rise.

Zinc Wall Panel Applications

Metal wall and façade panels are often selected to create a durable exterior skin that contributes to an overall high quality building envelope. Accordingly, wall panel manufacturers have developed innovative systems which use all the material qualities of zinc described above plus they have developed a range of systems supplied with preformed finishing accessories produced specifically for covering facades, for both new construction and renovation. Several types of wall panels include:

Flat Wall Panels

For walls, standing seam systems, either vertical or horizontal, are popular when using zinc. This traditional system allows long strips of profiled zinc panels to be assembled by forming single folds on the upstands. The sheets are laid on continuous sheathing and anchored using a combination of fixed and sliding clips. This system provides maximum water and wind resistance and is generally found to be an easy and cost effective installation. Further, it can be integrated with roofing systems for visual continuity, installed on curved surfaces, and applied to new or renovation projects. Smaller sized panels are also available primarily for flat facades that simplify installation but have more visible seams which may be desirable only in certain designs. 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.

Rain Screen Panels

Rainscreen applications are increasingly popular with design professionals and zinc is an excellent choice for this type of system. As with masonry rainscreen, flashing and weep holes need to be provided at the base, as well as the head details, of the exterior wall. An advantage with zinc wall construction is that it doesn't require caulking in the joints. This system utilizes an air cavity between the wall and cladding to produce a type of chimney effect that provides air flow and may improve energy efficiency. The wall behind the rainscreen is treated as the water barrier layer of the wall assembly with the anticipation that some water is allowed to penetrate the rainscreen surface. The flow of air in the cavity between the rainscreen and the water barrier allows for evaporation while also providing a means of drainage in this cavity down to the bottom. For rainscreen applications, both flatlock and interlocking systems are common. Flatlock panels are square or rectangular units that are attached to a substrate with their corners left open in order to allow condensation to drain or dry. These panels can be designed into facades using a running bond pattern, a stacked bond pattern, or even a diagonal diamond shaped pattern. The size and scale of the patterns will depend on which panels are selected, of course. Interlocking panels are mounted on hat channels placed either vertically (for horizontal panels) or horizontally (for vertical panels). These channels provide the required air flow as well as ability for water and condensation to weep out. They are intended to be fixed onto a framework of galvanized Z girts or hat channels as appropriate to the design using metal clips which are concealed in the inside edge of the groove. Many have the advantage of requiring no sealants, gaskets or butyl tape in the panel joints meaning no dirty streaks will be created from them and maintenance is notably reduced or eliminated. Regardless of the type of panel used, rainscreens are suited for both new and renovation projects since the fabricated metal panels give them great structural rigidity over long vertical and horizontal distances. Further, some panels can be designed and specified to be fully pressure equalized assuring the best ongoing performance over the life of the building. Finally, since the zinc metal panels are not laminated nor a composite, they will never delaminate.

Photo courtesy of VM Zinc, USA https://www.vmzinc-us.com/Sustainability.aspx Zinc wall panels installed as a rain screen with deep reveal joints in a stacked bond.

Decorative Shingles

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. 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. In some peaked roof applications, the gable end wall is enhanced by the use of decorative zinc shingles. These pre-formed, pieces are typically designed for overlapping, easy installation that produce very good weatherproofing on vertical wall surfaces and can be integrated with a full range of flashings for an all metal envelope where desired.

Using Zinc With Other Building Materials

Zinc metal products will provide the outer weathering barrier of the roofing or wall system, but obviously coordination with other building components is critically important. Trained and experienced installers are a must as with any 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 more structural support of their own, or be assembled in smaller panels to allow for greater flexibility. This is significant because certain products when placed in contact with zinc can have detrimental effects on the appearance and/or structural integrity of the zinc. In particular, zinc used in combination with copper and mild steel needs to be addressed, although there are no reactions with other metals. 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 due to the fact that zinc will become stained by the runoff. 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.

When looking at non-metallic products, zinc has been proven suitable adjacent to limestone since a number of limestone buildings in Paris have numerous zinc protective flashings 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.

Conclusion

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. Across the United States, design professionals increasingly turn to zinc for its inherent beauty, malleability and long-lasting appeal for commercial, public and residential projects. These buildings will stand the test of time, lasting for many, many years while reflecting their natural zinc patina for people to admire. Meanwhile, their owners will also enjoy these investments for their low-cost maintenance needs. Architectural zinc roofs and walls contribute to the industry's sustainable building ideals and the possibilities of unique design forms. As the misconceptions about zinc are cleared away, more professionals are choosing it for meeting customer demand for long-lasting, low maintenance products that can have a low impact on the environment.

Peter J. Arsenault, FAIA, NCARB, LEED-AP practices, consults, and writes about sustainable design and practice solutions nationwide. www.linkedin.com/in/pjaarch

Umicore Building Products is the world's leading producer of zinc construction products. Their roof panels and wall systems have been used on a wide array of prestigious buildings across the country. www.vmzinc-us.com