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Although the information contained in this Code has been obtained from sources believed to be reliable, New Zealand Metal Roofing Manufacturers Inc. makes no warranties or representations of any kind (express or implied) regarding the accuracy, adequacy, currency or completeness of the information, or that it is suitable for the intended use.

Compliance with this Code does not guarantee immunity from breach of any statutory requirements, the New Zealand Building Code or relevant Standards. The final responsibility for the correct design and specification rests with the designer and for its satisfactory execution with the contractor.

While most data have been compiled from case histories, trade experience and testing, small changes in the environment can produce marked differences in performance. The decision to use a particular material, and in what manner, is made at your own risk. The use of a particular material and method may, therefore, need to be modified to its intended end use and environment.

New Zealand Metal Roofing Manufacturers Inc., its directors, officers or employees shall not be responsible for any direct, indirect or special loss or damage arising from, as a consequence of, use of or reliance upon any information contained in this Code.

New Zealand Metal Roofing Manufacturers Inc. expressly disclaims any liability which is based on or arises out of the information or any errors, omissions or misstatements.

If reprinted, reproduced or used in any form, the New Zealand Metal Roofing Manufacturers Inc. (NZMRM) should be acknowledged as the source of information.

You should always refer to the current online Code of Practicefor the most recent updates on information contained in this Code.


This Code of Practice provides requirements, information and guidelines, to the Building Consent Authorities, the Building Certifier, Specifier, Designer, Licensed Building Practitioner, Trade Trainee, Installer and the end user on the design, installation, performance, and transportation of all metal roof and wall cladding used in New Zealand.

The calculations and the details contained in this Code of Practice provide a means of complying with the performance provisions of the NZBC and the requirements of the Health and Safety at Work Act 2015.

The scope of this document includes all buildings covered by NZS 3604, AS/NZS 1170 and those designed and built under specific engineering design.

It has been written and compiled from proven performance and cites a standard of acceptable practice agreed between manufacturers and roofing contractors.

The drawings and requirements contained in this Code illustrate acceptable trade practice, but recommended or better trade practice is also quoted as being a preferred alternative.

Because the environment and wind categories vary throughout New Zealand, acceptable trade practice must be altered accordingly; in severe environments and high wind design load categories, the requirements of the NZBC will only be met by using specific detailing as described in this Code.

The purpose of this Code of Practice is to present both Acceptable Trade Practice and Recommended Trade Practice, in a user-friendly format to ensure that the roof and wall cladding, flashings, drainage accessories, and fastenings will:

  • comply with the requirements of B1, B2, E1 E2 and E3 of the NZBC;
  • comply with the design loading requirements of AS/NZS 1170 and NZS 3604 and with AS/NZS 1562;
  • have and optimised lifespan; and
  • be weathertight.

COP v24.03:Durability; Special-Climates

4.7 Special Climates 

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.

4.7.1 West Coast, South Island, South Coast, North Island 

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.

4.7.2 Geothermal 

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.

4.7.3 Internal Environments 

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.

4.7.4 Fossil Fuel Residue 

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.