Copper Roofing

Copper has been used on roofs for centuries because it is durable, easy to form and solder, and needs no coating. It is installed as standing seam, batten seam, flat seam and horizontal seam roofs, and is also common for flashings, gutters, domes, cupolas and bay roofs. Philadelphia's Christ Church (1727 to 1744) had a standing seam copper roof; until the end of the eighteenth century, sheet for American roofs was imported from England.

Material

North American specifications call for cold-rolled copper to ASTM B370, usually in temper H00. Copper is sold by weight per area:

• 16 oz/ft2: about 0.0216 in (0.55 mm), roughly 24 gauge.
• 20 oz/ft2: about 0.0270 in (0.69 mm), roughly 22 gauge.

Elsewhere copper sheet is specified directly in millimetres.

Installation basics

• Pans are held by concealed copper cleats, typically at about 12 in (300 mm) centres, so they can expand and contract.
• A rosin-sized paper slip sheet is laid over the underlayment so that heat-softened asphalt does not glue the copper to the deck.
• Nails are copper or bronze; screws and bolts are copper, bronze, brass or 300-series stainless steel.
• Contact with incompatible metals or corrosive substrates is prevented with a bituminous coating or another permanent separator.
• Joints on low-slope roofs are soldered; tinned edges are typically 1.5 in (38 mm) wide.

Weathering and run-off

Copper changes colour over years, from salmon pink through browns to a blue-green or grey-green patina whose timing depends on climate. Run-off can stain stone, brick and concrete and will attack aluminium and zinc-coated steel downstream.

Life and cost

Properly installed copper roofs are commonly cited at 100 years or more. The metal is expensive but fully recyclable, and old copper is usually salvaged.