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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; Accessories

4.19 Accessories 

4.19.1 Fastener Durability 

All cladding fasteners must be compatible with the material, suitable for the environment and a durability equivalent to that of the cladding material. All exposed fasteners must have a minimum durability of Class 4. (See 17 Testing and MRM Standards)

Only aluminium or stainless steel screws and washers should be used on pre-painted aluminium roof and wall cladding. Stainless steel fasteners must not be allowed to come into contact with the cladding and should be installed through oversize holes.

Sealing washers must be non-conductive to prevent electrical contact between the screw, the metal washer and the cladding surface.

Steel cladding screws can be subject to hydrogen embrittlement when they are hot dipped galvanised. Alternative methods of galvanising, such as peen plating and other metallic coatings, are generally used in combination with an organic coating.

Care should be taken to minimise damage to the head of the nail or screw when using colour matched painted hot-dipped galvanised nails, bolts and screws.

Sandblasting in exposed conditions can significantly reduce the coating thickness and the longevity of the fastener.

Premature failure can result when the shanks of the screws and the eaves purlin are exposed to sea spray, and a high-fronted gutter is recommended to help prevent this.

The performance of the shank of the fastener is also affected by internal environments when the contaminant is inside the building, e.g., animal shelters, fertiliser works.

 All fasteners should be easily identified by a code stamped on the head to identify the manufacturer and the coating class.

4.19.2 Screw Guns 

To avoid damage to the coating to the screw-head, drivers should not be of the impact type and should be fitted with a snug fitting driver bit.

4.19.3 Sealant 

Sealant should be neutral cure silicone or MS polymer.

4.19.4 Underlay 

Underlay should have durability no less than the cladding material, and be compatible in contact with the roofing material.

4.19.5 Underlay Support 

Galvanised wire netting or mesh can be used to support underlay where the internal environment is not aggressive, but is not to be used with painted aluminium.

Plastic mesh, tape or string may be used to give support at a maximum of 300 mm centres. These alternatives should be used when underlay support is required with aluminium cladding. Ensure that the underlay-support fasteners do not come in contact with the underside of the cladding.

For buildings with harsh internal environments, stainless steel, or PVC-coated mesh and netting are available.  PVC-coated mesh may suffer degradation from UV radiation if used externally or when it is exposed to high levels of direct or reflected sunlight.