What is the difference between zinc and galvanized steel for roofing?

Zinc is a pure or near-pure zinc alloy rolled to precise thickness for architectural roofing. Galvanized steel is steel coated with a thin layer of zinc to prevent corrosion. Architectural zinc develops a consistent blue-grey patina and lasts 80 to 100 years. Galvanized steel does not develop the same patina and has a shorter service life. They are not substitutes.

Does zinc roofing turn green like copper?

No. Zinc develops a zinc carbonate patina — matte blue-grey, not green. The green patina on copper is copper sulfate, specific to copper chemistry. Zinc and copper weather by entirely different chemical processes and to entirely different colors.

Is zinc appropriate for gutters and downspouts as well as roofing?

Yes. Zinc half-round gutters and round downspouts are correct with zinc roofing and develop the same blue-grey patina. They should not be mixed with copper elements, as galvanic corrosion occurs where dissimilar metals contact each other in the presence of water.

Zinc — Old Canaan Building Materials

Zinc is not copper. It does not turn green. It turns blue-grey — a specific, quiet, matte blue-grey that is one of the most beautiful roof colors in a New England landscape — and it stays that way. It is a material that has found its correct place on traditional buildings where the warmth of copper is wrong and the coldness of painted steel is also wrong.

The Character

Freshly installed, zinc is a bright metallic silver. Over the first two to three years, the zinc carbonate patina develops — a matte, even blue-grey that absorbs rather than reflects light. It is not as warm as copper. It is not as industrial as galvanized steel. It is a refined, cool grey that recedes into a New England sky.

What It Is

Architectural zinc for roofing and cladding is a zinc-titanium alloy — primarily zinc with small additions of titanium and copper for improved strength and creep resistance. The standard product is VM Zinc or Rheinzink, in 0.8mm to 1.0mm thickness for standing seam roofing. It is available pre-weathered (QUARTZ-ZINC, already the matte grey) or bright, which weathers naturally over several years. Standing seam zinc is installed with concealed clips that allow thermal movement — zinc has a higher coefficient of thermal expansion than copper and must be detailed accordingly.

How It Behaves

Zinc is fully recyclable and self-healing at minor scratches — the patina reforms over surface abrasion. It should not be installed in contact with cedar, treated lumber, or in situations where copper-bearing water drains over it. It performs well in New England conditions and has a documented service life of 80 to 100 years on well-designed roofs. It requires a vented substrate — zinc should not be installed directly over impermeable sheathing without ventilation below.

Why It's Right

On buildings where copper reads too warm — a grey-shingled house, a building with a cool stone palette, a contemporary interpretation of a traditional vernacular — zinc is the correct metal roof. It does not compete with the building. It completes it.

How To Get It

Through architectural metal roofing contractors who work with zinc. Specify VM Zinc or Rheinzink pre-weathered (QUARTZ-ZINC finish) for immediate patina character, or natural finish if the weathering sequence is acceptable. Confirm the installer has specific zinc experience — zinc detailing is different from copper and steel.

The Old Canaan Standard

VM Zinc or Rheinzink, 0.8mm minimum thickness, pre-weathered QUARTZ-ZINC finish, standing seam profile, for roofing on traditional New England buildings where a cool grey metal roof is the correct specification. Vented substrate required. No contact with cedar or copper-bearing water. The blue-grey patina is the finish. It is not provisional.

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