Terne Plate

Terne plate (terneplate) was thin iron, and later steel, coated by hot-dipping in an alloy of lead and tin. The coating was typically 10 to 20% tin and the rest lead. The name is usually traced to a French word for dull, describing its matte look compared with bright tinplate, which carried a pure tin coating.

Use in roofing

Because the low tin content made it cheaper than tinplate, terne became a common roofing metal in the nineteenth and twentieth centuries, often installed as flat seam or standing seam roofs and as flashings and gutters. Old records frequently describe terne roofs as "tin" roofs, and the two are easy to confuse.

Maintenance

Terne roofs are iron-based and must be painted. Preservation guidance stresses that the underside should be primed before installation and the exposed face kept painted. With paint maintained, terne roofs are reported to last 90 years or more; neglected roofs rust through.

End of production

Lead's toxicity led manufacturers to replace it with a tin-zinc alloy, and traditional terne-coated carbon steel is no longer sold. Repairs and replacements on historic buildings now generally use terne-coated stainless steel (a tin coating over stainless) or copper.

Conservation notes

When an old terne roof is repaired, matching the seam type, pan size and colour of the original helps keep the building's character. Lead-based coatings on surviving sheets require appropriate care during removal or soldering.

Related materials

Terne plate sat between tinplate and galvanized iron in cost and appearance. Zinc-coated (galvanized) iron, developed in France in 1837, gradually took over many uses because it did not need constant painting, while copper remained the premium choice for important buildings.