The Contemporary Architecture with Zinc
Zinc is a non-ferrous metal that provides an effective solution for the coating of buildings that are exposed to adverse weather conditions, while at the same time providing an innovative response to program requirements and project users.
Zinc roof sheets create a self-protecting layer when in contact with humidity that isolates heat from indoor spaces during the summer. Rain and snow can easily slip over its surfaces and its modular panels can wrap curved shapes or be perforated according to the architectural design and mixed into various shades, brightness, and colours in façades and/or ceilings.
Relative to other sheet metal materials, zinc roof sheets are advertised for their low life cycle costs. Copper, aluminium, and stainless steel are comparable in material cost to sheet metal zinc. In general, the service life of zinc roofing is estimated to be 70 years; however, some buildings have sections of original zinc roofing that work well up to 120 years after installation.
Bring on the Water
The same process that allows the development of a protective patina on the surface of exposed zinc may be detrimental under unique conditions. To create a thin layer of zinc oxide, near-pure zinc exposed to the atmosphere can react with oxygen. It produces zinc hydroxide when the zinc oxide layer is exposed to humidity. Zinc hydroxide reacts with carbon dioxide in the atmosphere to form zinc hydroxyl carbonate as the moisture is drained from the surface of the metal.
A robust, well-bonded zinc hydroxyl carbonate layer is usually formed on the surface of the metal following repeated wetting and drying cycles. Zinc hydroxyl carbonate is a durable material that, in the presence of water, does not react and acts as a protective patina layer to regulate the exposed zinc's corrosion rate.
The Fight against Leaks
Although architectural zinc roof sheets are built to prevent leakage of bulk water, they are called water-shedding roof systems, and small amounts of water are likely to bypass the panels under some detailed conditions. For this purpose, metal panel roofs have traditionally been built to absorb and drain incidental leakage water from the structure with continuous roofing substratum. Most zinc roof sheets materials can withstand minor water leakage by thorough conditions of metal roofing without shortening the roofing material's service life.
The Issue of Backside Corrosion
In the event of minor roof leak or condensation, some zinc producers add a coating on the backside to protect the zinc roof sheets from backside corrosion. Usually, the coating is a factory-applied organic paint that differs between manufacturers in thickness. The coating is applied to avoid moisture from wetting the zinc. However, authors have found that this coating is not efficient in preventing corrosion where the oxidation of the coating was caused by moisture and then zinc in a manner consistent with normal uncoated zinc backside corrosion.
It is generally referred to as ventilation to provide airspace under zinc roofing, which means a certain amount of airflow through space. However, it is more important to lift the zinc off the substrate based on the experience of the authors to avoid contact between the zinc roof sheets and any accidental leakage of water, rather than to provide a certain amount of ventilation air exchanges inside the room. Misconceptions about the purpose of the ventilation system and how it works continue.
To reduce the risk of accidental leakage behind the roofing, the detailing of zinc roof sheets is important to prevent exposure of the panel to direct contact with water. Detailed panel closures, ridges, hips, and rising walls should receive special attention. To shape turned-up pans, panel closures at ridges and hips should not be cut as this results in reliance on sealant to protect against leakage. Panel closures can instead be manufactured using a bread-pan system that folds the panel in a way that produces a pan without cutting the panel.