ASTM B370

ASTM B370, Standard Specification for Copper Sheet and Strip for Building Construction, covers rolled copper sheet and strip in flat lengths or coils for roofing, cladding, flashings, gutters, downspouts and general sheet metal work. The active edition is ASTM B370-22. The standard notes that products made to it are not intended for electrical uses.

Tempers

Copper's hardness (temper) affects how easily it can be formed and how well it holds its shape. B370 lists tempers including:

• O60 – soft
• H00 – cold-rolled (often called eighth-hard)
• H01 – cold-rolled, high-yield (quarter-hard)
• H02 – half-hard
• H03 – three-quarter hard
• H04 – hard

Cold-rolled copper is the most common temper in US building construction because it is much stronger than soft copper while still workable. Eighth-hard cold-rolled copper is often recommended for roofing and flashing, and quarter-hard high-yield copper is used mainly for flashing where strength and some formability are both needed. Soft copper is used for intricate forming and where it must conform to irregular shapes.

Thickness by weight

In the United States, architectural copper thickness is usually stated as weight in ounces per square foot. Common construction weights range from about 12 oz to 48 oz per square foot; gutters and downspouts often use 16 oz or 20 oz copper. In Europe, roofing copper is usually specified by thickness, typically 0.6 to 0.7 mm (about 0.024 to 0.028 in).

Durability

Copper forms a protective patina that progresses from oxides to darker sulfides and eventually to the green basic sulfate familiar on old roofs. Full green patina may take around 7 to 9 years in marine air and 15 to 25 years in industrial settings, and longer in clean rural air. Once formed, corrosion is very slow, so properly detailed copper roofs can last for centuries.

Related standards

In Europe, copper sheet for building is covered by a separate European Standard. Copper roofing systems such as standing seam, batten seam and flat-lock soldered roofs are installed following trade guidance rather than B370 itself.