In areas where humidity or local conditions create an increased likelihood of corrosion, special consideration should be given to the specification and use of metal roof and wall cladding and accessories.
COP v23.09:Durability; Special-Climates
The West Coast is characterised by high rainfall and a very severe coastal environment between the sea and the Southern Alps; many households have coal burning fires that produce sulphur dioxide that is detrimental to metals.The combination of these factors means that either a shorter performance life should be accepted or the use of more durable metals and coatings considered.
The North Island’s south coast not only has strong onshore prevailing winds, but strong current flows increase wave action and the amount of salt-laden air, creating a particularly harsh marine environment.
Buildings within 50 m of a geothermal fumarole are considered to have a geothermal microclimate, which causes increased corrosion due to higher humidity levels combined with hydrogen sulphide.
Highly active geothermal areas, such as much of Rotorua, are considered geothermal, even in the absence of a local fumarole.
Corrosive internal environments with high humidity, causing condensation, and pollutants generated within the building can also affect neighbouring buildings. These include:
- covered swimming pools;
- fertiliser works;
- meat works;
- animal sheds or shelters;
- pulp and paper manufacturing; and
- vehicle exhaust fumes.
Sulphur dioxide develops when burning fossil fuels. After oxidation and reaction with water it forms sulphuric acid (H2SO4) that can contribute considerably to the atmospheric corrosion of zinc and steel.
Burning resinous woods, CCA-treated timber, low-grade coal or oils with a high sulphur content can increase the fall-out deposit or condensate from flue gas.
Exhaust fans can cause similar problems when corrosive gases are not filtered at their source.