Zinc roofing has been extensively used in Europe for over two centuries, and was introduced into the U.S. market in the 1990s. Zinc is a naturally weathering material that many building designers admire due to its rich coloring and matte finish. However, zinc is prone to premature corrosion when the backside is exposed to repeated contact with water in the absence of air. Manufacturers and architects have used various methods to prevent water from causing accelerated backside corrosion of zinc products. It is relatively frequent practice to provide a ventilation space beneath zinc panels to allow airflow beneath the zinc panels to promote drying. Over the years, we have seen multiple zinc roof failures associated with backside corrosion due to material selection, and improper flashing and ventilation detailing. 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.
Zinc roofing has been used extensively in Europe for over two centuries and, more recently, has gained popularity in the U.S. 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). Architectural-grade zinc is malleable, relatively strong and can be field-soldered, lending itself to use in irregular architectural profiles. The material is also versatile, and can be used as both roofing and cladding allowing for smooth transitions between the assemblies, where desired.