Zinc Roofing (Titanium-Zinc)

Architectural zinc, often called titanium-zinc, is nearly pure zinc alloyed with small additions of copper and titanium. It is used for standing seam roofs, wall cladding, gutters and flashings, and is especially traditional in France, Belgium, Germany and the Netherlands. Paris rooftops, many dating from the late nineteenth century under Napoleon III, are still largely zinc.

Alloy and standard

Building zinc is made to the European standard EN 988. Typical trace contents are copper about 0.08 to 1.0%, titanium about 0.06 to 0.2% and aluminium under 0.015%. Copper raises strength; titanium improves resistance to creep, the slow downhill stretching that soft metals suffer on a roof.

Patina

Bright zinc reacts with moisture and carbon dioxide to form a grey layer of zinc hydroxy-carbonate, typically over 2 to 5 years and faster in polluted air. The layer heals itself when scratched. Factory pre-weathered zinc gives the grey colour from the start.

Design rules

• Ventilation: moisture trapped on the underside causes white corrosion. Zinc is laid over ventilated decks, drainage mats or skip sheathing, or uses a factory backside coating.
• Thermal movement: zinc moves about 1 in per 30 ft (roughly 25 mm per 9 m); roofs combine a fixed zone with sliding clips.
• Cold forming: zinc can crack if folded below about 7 degrees C (45 degrees F); installers warm it in cold weather.
• Contamination: salt spray, acid rain and masonry dust can mark or accelerate corrosion.
• Compatibility: copper run-off and contact with copper should be avoided.

Life and environment

A properly installed zinc roof is commonly cited at 60 to 100 years, with weathering rates of about 1 to 7 micrometres per year depending on pollution. Zinc is widely recycled and needs less energy to refine than aluminium, copper or steel.