![]() ![]() ![]() Several variations of separation mats have been used over the years in zinc roofing installations in an attempt to “ventilate” beneath the zinc panel. Common methods to prevent backside corrosion include: providing a “ventilation” space beneath the roofing, using three-dimensional polymer separation mats for venting, and applying organic coatings to the backside of the zinc sheets, resulting in variable degrees of success. Since the major introduction of zinc roofing, manufacturers have used various methods to control accelerated backside corrosion of zinc products. The same corrosion process occurs on galvanized steel (steel coated with nearly pure zinc coating), and occurrences of “wet storage stain”, and its prevention, have been well documented in the industry for decades. This process of zinc corrosion on the backside of metal roofing panels has been well documented in the industry for many years. However, zinc products do not tolerate minor roof leakage or condensation without allowing corrosion that can eventually lead to failure of the roofing material. Most metal roofing materials can tolerate minor water leakage through metal roofing detail conditions without shortening the service life of the roofing material. ![]() For this reason, metal panel roofs have historically been designed with continuous roofing underlayment to collect and drain incidental leakage water from the system. While architectural-grade zinc has many properties that make it a natural choice for use on building enclosures, the material is susceptible to premature corrosion if not designed and installed properly.Īlthough architectural metal roofs are designed to prevent bulk water leakage, they are considered “water-shedding” roof systems, and it is anticipated that small amounts of water may bypass the panels at certain detail conditions. At the end of service, virtually all the zinc material can be recycled and recovered for use in galvanizing. While some metals may require recoating over time, if zinc panels are scratched new patina will form on the exposed freshly exposed zinc. While in service, zinc panels require minimal maintenance due to the natural formation of a protective patina when exposed to the atmosphere. The service life of zinc roofing is generally estimated at 70 years however, some buildings in Europe have portions of original zinc roofing performing well up to 120 years after installation. Material costs for sheet metal zinc are similar to copper, aluminum, and stainless steel. Zinc roofing and cladding is marketed for its low-life cycle costs relative to other sheet metal products. ![]() The material is also versatile, and can be used as both roofing and cladding allowing for smooth transitions between the assemblies, where desired. Architectural-grade zinc is malleable, relatively strong and can be field-soldered, lending itself to use in irregular architectural profiles. Zinc is a naturally weathering material that many building designers admire due to its rich blue-gray coloring, matte finish and natural appearance ( Photo 1). Zinc roofing has been used extensively in Europe for over two centuries and, more recently, has gained popularity in the U.S. This article will provide a comprehensive explanation of the zinc corrosion mechanism, and will discuss the nuances of properly designing zinc roofs and cladding to minimize leakage and the risk of backside corrosion. Over the years, we have seen multiple zinc roof failures associated with backside corrosion due to material selection, and improper flashing and ventilation detailing. It is relatively frequent practice to provide a ventilation space beneath zinc panels to allow airflow beneath the zinc panels to promote drying. Manufacturers and architects have used various methods to prevent water from causing accelerated backside corrosion of zinc products. However, zinc is prone to premature corrosion when the backside is exposed to repeated contact with water in the absence of air. Zinc is a naturally weathering material that many building designers admire due to its rich coloring and matte finish. Zinc roofing has been extensively used in Europe for over two centuries, and was introduced into the U.S. ![]()
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