For centuries, zinc roofing materials have proven reliable in Europe’s marine environments and other extreme climates. In recent decades, the enduring qualities of zinc have gained interest and use in North America. Here are five aspects to consider when working with zinc in coastal roofing applications.
1. Natural Material
Zinc is an abundant natural resource. Based on known ore reserves, the world’s zinc supply is estimated in excess of 200 million tons and expected to last approximately 700 years.
Zinc’s inherent metallic properties allow the material to deliver non-corrosive, self-healing, low-maintenance and long-lasting performance. No paint, varnish or sealants are required, and its run-off is non-staining and non-toxic.
In North America, ASTM B69-16, “Standards Specification for Rolled Zinc,” is the primary reference document for both Type 1 and Type 2 alloys and their expected characteristics. Rolled zinc is efficiently produced by alloying Special High-Grade, 99.995 percent pure zinc with very small quantities of copper, titanium and aluminum. The zinc alloy composition determines whether the metal will tend toward a blue-gray or graphite-gray coloration.
2. Dynamic Appearance
A time-proven, dependable material, zinc roofing products complement both contemporary and traditional architectural styles, and foster a connection to their surrounding natural environment.
Untreated, architectural-grade zinc is bright, shiny and light reflective. Over time, a natural matte patina develops, creating a dynamic appearance as the material ages. A patina’s formation is a process of the gradual growing together of zinc carbonate “freckles.” The rate of its formation is related to the slope of the surface. The patina will form slower on a vertical wall surface than on a slightly pitched roof. The patination speed varies between six months and five years or more, depending on climatic conditions. The more exposure to wetting and drying cycles, the quicker the patina will develop.
Specific to coastal communities, the natural patina will appear lighter when used in marine locations where the air contains chlorides (salt). Deposits will not be as visible on lighter blue-gray zinc.
Some manufacturers offer pre-weathered zinc material that accelerates the patina formation under controlled conditions. Factory-finished options also are available to achieve an initial, uniform aesthetic.
3. Product Versatility and Variety
A soft, lightweight metal, zinc can be fabricated to fit almost any slope, curve or linear run, as well as perforated and fashioned into ornamental accents. Zinc roofing products can be installed on low sloped, steep sloped, flat and mansard roofs, and used for hip and ridge caps, drip edges, alleys, step flashing, dormers, cupolas, parapets and more.
Seam profiles can be customized to the project’s requirements. For example:
· Double-lock and single-lock seam joints between roof panels stand 1 inch or 1.5 inches up from the draining plane. A raised seam height can emphasize the roof as a design element and have a functional purpose in coastal climates with snow.
· Vertical standing seam profiles with mechanical lock connections are the most common zinc roofs.
· Flat seam profiles rely on gravity and at least a 4:12 slope to maintain weathertightness.
· Low-profile zinc shingles and interlocking or overlapping tiles applied parallel to the eave present another familiar aesthetic. They involve a technically easier installation method than vertical joints and always are applied as a “dry-joint” roof system without solder or sealant. Tiles can be small. They provide good wind resistance, but cannot provide the same level of weather protection as a vertical seam.
· For vertical seam profiles, vertical joints are attached to one vertical side joint, overlapped and closed on the opposite side. The soft metal simplifies the task of hand-seaming or power-seaming zinc panels. Long panel lengths can make this design more vulnerable to oil-canning (panel waviness), panel disengagement and wind uplift. Accommodating longer panels, taller seams and those with added capillary breaks offer better water and wind resistance, critical in many coastal applications.
4. Resilient Results
Installed properly, zinc roofing systems will resist corrosion, air and water infiltration, and withstand high winds reaching up to 150 mph. In marine environments that are susceptible to fires, zinc also offers a noncombustible solution.
Common installation considerations and cautions include:
· Zinc roof profiles should be applied as a ventilated dry-joint cladding or a “rainscreen” roof strategy, not as the primary waterproof barrier. This design alternative allows for pressure equalization, backside drying and moisture escape.
· Above-sheathing ventilation mats must be a requirement of every zinc roof assembly. Use an 8 to 10 mm structured underlayment comprised of entangled nylon wire to elevate the zinc roof panel, creating a capillary break with a 0.95 cm airspace to help keep the underside of the profile dry. Do not accept a substitution of this air space and capillary break with a backside paint coating or other barrier strategy.
· Self-adhered high-temperature roof underlayments are recommended. Synthetic felts may be utilized on steep pitch roofs in combination with self-adhered high-temperature underlayments at vulnerable roof conditions and roof penetrations.
· Red rosin paper, conventional felt and any other moisture-holding material should be prohibited in every zinc application and related specification.
· To facilitate moisture drainage from the vented space, the roof panel usually should have a soft bend past the drip edge (cleat). This open hook promotes water drainage from the end pocket formed by the panel hook. Zinc profile end folds also should be “soft” with the raw zinc edge parallel to the ground and not closed tight.
· Excessive use of sealants can plug weep holes, limit airflow, trap moisture, create adverse reactions or restrict the metal’s movement. For any proposed use of tube or tape sealants within laps or other concealed applications, first consult the zinc manufacturer.
5. Sustainability and Longevity
The sustainable benefits of architectural zinc products support criteria for several green building programs including BREEAM certification, the Green Globes system, the U.S. Green Building Council’s LEED rating system, and the Cradle to Cradle Products Innovation Institute.
Products that have earned Cradle to Cradle certification demonstrate their product’s material does not release any toxic substances during usage, deconstruction and recycling; that it retains its original properties without loss of performance; and that can be re-used as a new item of at least equal value. This is known as upcycling; whereas downcycling results in recycling material to become inferior products, and non-recyclable products will be sent to a landfill. More than 90 percent of zinc-containing products are recycled at the end of their lifecycle.
During their many years of use, zinc roofs do not rot, rust or need repainting. They require very little maintenance. For aesthetic reasons, it is recommended to clean the surface of the material with clean water (not seawater) at least twice a year in maritime climate zones, depending on local conditions. Follow the manufacturer’s cleaning instructions. If the metal is scratched, scuffed or fingerprinted, zinc will heal itself by re-patinating. With time and exposure to wetting and drying cycles, the former blemish will patinate and blend to match.
The resilient performance and natural beauty of zinc has been demonstrated for more than 200 years in marine environments and coastal communities. Collaboration between roofing contractors and zinc manufacturers will help ensure a roof that provides long-lasting functionality and appearance, achieving the best results for the building owner.
About the author: Charles “Chip” McGowan is president of RHEINZINK America, Inc., providing architectural-grade zinc materials for roofing and wall cladding systems throughout North America. He can be reached at firstname.lastname@example.org. For more information, visit www.rheinzink.us.