Galvanic corrosion
Galvanic corrosion occurs when dissimilar metals contact in the presence of moisture, accelerating decay. Prohibited metal pairings are listed in NCC 2022 HP 7.2.
Ask Chalkline about this →Galvanic corrosion is the accelerated decay of one metal caused by contact with a dissimilar metal in the presence of an electrolyte (typically moisture or rainwater). The more reactive (anodic) metal corrodes faster than it would alone; the less reactive (cathodic) metal is protected. In building, the effect is most pronounced on roofing and flashings where dissimilar metals are physically adjacent and regularly wetted.
Common problem pairings on residential sites include lead flashings against Colorbond or Zincalume steel (prohibited under NCC 2022 HP 7.2.3), copper gutters or downpipes paired with zinc-aluminium (Zincalume) or galvanised steel roofing (copper ions in runoff accelerate corrosion of the steel downstream), and steel screws in aluminium sheeting. NCC 2022 Housing Provisions Part 7.2 Table 7.2.2b sets out compatible fastener and material pairings to prevent this.
Also known as: galvanic action, bimetallic corrosion.
Category: Materials / building envelope.
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Last updated: 2026-05-08. Verified: 2026-05-08. Quarterly review for currency.