Corrosion Protection for Sheet Metal Roofing (NAT)

When designing and specifying metal roofing it is important to take into account the location of the building and whether the roof will be exposed to either airborne salt in coastal areas or the effects of heavy industrial areas through airborne pollution.

Unless a material that is ‘fit for purpose’ is used the result may be corrosion of the metal roofing which may lead to costly repairs.

The Building Code of Australia (BCA) provides information on appropriate corrosion protection of metal roofing and it is required to follow these provisions to ensure compliance and proper protection of the roof.

This table has been taken from the BCA Volume 2 and provides information on the correct level of protection required depending on the environment.

Extract from BCA 2011, Australian Building Codes Board

It is important to note that it should not be assumed that the roofing you are using is suitable for the purpose. As stated under Metallic and organic coating the level of galvanised or zinc/aluminium coating will not be sufficient for severe areas.

The Australian Standard in relation to hot-dip zinc coated and aluminium/zinc coated steel, AS 1397, provides guidelines on the nature of various coating classes and typical applications for both galvanised and zinc/aluminium roofing or steel.

The Standard notes that a Z450 galvanised and an AZ 150 zinc/aluminium coating is the recommended coating for typical exterior applications e.g. roofing, claddings and accessories and a Z275 is acceptable for general purpose coatings, where an AZ 200 coating is heavy duty coating designed for culverts and box gutters.

In the case of the BCA the AZ200 (zinc/aluminium) is the only level of coating suitable in those coastal or industrial areas so it would be prudent to check with your supplier that the correct material is being provided for the appropriate application and location.
For further information HIA members can contact HIA’s Building Services staff on 1300 650 620 or hia_technical@hia.com.au.   

If you would like to become a HIA member, contact 1300 650 620 or enquiry@hia.com.au

The above is intended to provide general information in summary form. The contents do not constitute specific advice and should not be relied upon as such. Formal specific advice should be sought by members with respect to particular matters before taking action.  ABN 99 004 631 752