The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
To understand metal performance in any specific environment, the unique properties of each metal should be considered in conjunction with other metals it is used with.
All metals react differently to the atmosphere and to any contaminants that come into contact with their surface by rain, wind or condensation. The indicator of acidity or alkalinity is pH, measured from 0 – 14; acidity/alkalinity is an important corrosion factor. pH 7 is neutral, below 7 is more acidic, above 7 is more alkaline.
As can be seen from the graph above, zinc performs better in alkaline environments, and aluminium performs better in acidic environments.
Aluminium-zinc coatings should be avoided in buildings such as closed animal shelters or fertiliser storage sheds, where alkalinity may be high.