A zinc-copper-titanium alloy rather than pure zinc. The copper raises strength and the titanium sharply improves creep resistance, which is what makes the material viable on a roof under sustained load and thermal cycling. Pure zinc creeps at ambient temperature and would deform over time in the same application.

Sheet given its grey patina at the factory by a controlled chemical process, so it arrives looking as bright rolled zinc will look after several years of exposure. It is specified where uniform appearance from day one matters, or where different phases of a building would otherwise weather at visibly different rates.

Roughly twice as much as steel, and that governs the detailing rather than being a footnote. Maximum panel and gutter lengths, the use of sliding versus fixed clips, and the position and size of expansion joints all follow from it. Restraining a long run rigidly causes buckling and fatigue cracking at fixings.

Alkaline run-off from fresh cement, mortar and concrete; tannins leached from unseasoned oak and western red cedar; and run-off from any copper surface upstream in the drainage path, which plates out and sets up a galvanic cell. Trapped moisture on the underside also causes corrosion, so ventilated substrates are standard.

Traditionally, yes - with a zinc chloride flux and a suitable solder, and it remains the way watertight joints are closed in gutters, flashings and rainwater goods. Most roofing joints are formed rather than soldered - folded, welted and seamed - with soldering reserved for details where a mechanical joint cannot be made watertight.

In cold conditions, yes. Below roughly 10 degrees Celsius zinc loses ductility noticeably and tight bends and welts can crack. Site practice is to warm the material or the work area before forming in winter, and to allow more generous radii where warming is impractical.

Typically many decades, and often the life of the building, because the patina is self-healing and continues to protect the metal. Actual life depends on the atmosphere - it is shorter in heavily polluted or marine environments - and on whether the underside is ventilated, since trapped moisture attacks the unpatinated face.