Architectural Zinc Roofing:
Product advantages and selection considerations
Zinc’s design flexibility, longevity, sustainability and natural beauty make it a highly desirable product for roofing. Often preferred for steep-sloped roofs, zinc also works well on valleys, hip and ridge caps, drip edges, step flashing, dormers, cupolas, parapets, gutter systems, downspouts, ornamental elements, and more.
Zinc is a natural, soft metal. Its natural metallic properties contribute to roofing products’ self-healing, low-maintenance, corrosion-resistant performance without the need of paint, varnish or sealants. Used in roofing systems, it has a potential lifespan of 80 years or more. At the end of its useful life, it remains 100 per cent recyclable.
Used in Europe since the 1800s, zinc roofing relies on a time-proven, dependable material and provides an attractive patina as it ages. Zinc’s character constantly evolves in its depth, complexity and rich appearance. Combining a timeless appearance with a natural patina and time-tested performance that can last generations, RHEINZINK America, Inc. offers architectural grade zinc roofing products in CLASSIC® bright rolled, prePATINA® blue-gray and graphite-gray, and artCOLOR® in an array of colors.
Just as copper ages from shiny orange to powdered green, zinc develops its distinctive patina based on the alloy composition. All of RHEINZINK America’s products rely on high-grade zinc with trace elements of titanium and copper. RHEINZINK products meet the ASTM standard specification B69-16 Architectural Rolled Zinc Type 1 and Type 2. Currently, RHEINZINK is the only manufacturer with a Type 2 designation, which was received for its prePATINA graphite-grey alloy. RHEINZINK prePATINA products are specially processed to begin achieving this aesthetic prior to installation.
The patination of zinc architectural products forms through a two-step chemical reaction: combining with water and oxygen to form zinc hydroxide, and combining with carbon dioxide in free-flowing air.
This generates a dense outer layer insoluble to water and a packed inner layer of alkaline zinc carbonate.
The weathering characteristics of a patina’s formation is a process of the gradual growing together of patinated ‘freckles’ and the rate of its formation is related to the slope of the surface.
The patina will form faster on a slightly pitched roof than on a vertical wall surface. Ultimately, the natural patina form to a more uniform color.
The slope-related patination speed can vary between six months and five years, depending on climatic conditions. The more exposure to wetting and drying cycles, the quicker the patina will develop.
While the basis of the patina is alkaline zinc carbonate, additional substances are incorporated from the local humidity, rainfall, snowfall, and air pollution levels. This is why the color of the patina can vary slightly from one place to another. The natural patina will appear lighter when used in marine locations where the air contains chlorides.
When used in environments where sulphur levels are higher, the patina may appear somewhat darker. In most environments, the surface does not typically require maintenance and only need minimal cleaning throughout its lifetime.
Designed in traditional or modern architectural styles, zinc roofing applications include double lock and single lock, interlocking tiles, and batten seam roofs. Roof slope and scale, local weather conditions, and warranty requirements influence the seam type selection.
Double-Lock Standing Seam pre-profiled panels are ideal for roof pitches greater than 5/8:12, for creating curves and custom shapes, and for integral snow-retention or photovoltaic systems.
Angle-Lock Standing Seam panels offer distinctive lines and shadows with a wider profile seam than the Double-Lock, and also can integrate snow-retention or photovoltaic systems. Along with a conventional vertical orientation, the panels can be installed horizontally or diagonally, and on rounded parapets or mansard roofs, and on roof pitches greater than 6:12.
Batten Seams are used in traditional wide-seamed applications, as an alternative to Double-Lock Standing Seam or in combination with standing seam panels. Available in up to 60-foot lengths, the batten seam panels form the boxlike joints by lengthwise connections with a wood batten or a RHEINZINK galvanized steel clip.
Interlocking tiles are individually sized in diamond and rectangular shapes to create a unique aesthetic for roofs with complex geometry, with curvilinear surfaces and with roof pitches greater than 3:12.
Specifications that outline seam style, height, panel widths, and closures will reduce confusion, as well as the potential for errors. A general specification recommendation for water-check folds at the top of the lap and staggering of traverse seams also should be prescribed.
Attachment of all zinc panels should accommodate panel movement of approximately six centimetres (0.25 inches) per 305 centimetres (120 inches) per 55ºC (100ºF) temperature change. The total design temperature fluctuation should be 67ºC (220ºF). Based on the metal temperature at the time of installation, the contractor should calculate the maximum movement and ensure that the panel ends do not disengage or ‘bottom out’ in extreme conditions. Please remember that differences in climate conditions and exposure also can produce different aesthetic results.
In order to achieve specified appearance and performance, you need to be aware that zinc manufacturers are not synonymous with system suppliers, fabricators, or installers of zinc products.
Working with experienced zinc manufacturer and regional fabricator through design, specification, and installation will help to ensure the project’s roof will provide the natural look, specified performance, and up to a century of use.
About the Author
Charles (Chip) McGowan is the president of RHEINZINK America, Inc., which led the introduction of architectural zinc in North America. McGowan has been involved with the distribution of natural metals for more than 30 years, specializing in manufacturing, sales and technical advisement. He can be reached at 781-729-0812 or firstname.lastname@example.org