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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 v23.12:Installation; Accepting-Delivery

14.3 Accepting Delivery 

Check the delivery to make sure you have the right product, delivered in prime condition. If there is any concern about the condition of the product, the supplier should be contacted before installation commences.

Ensure all components needed to complete the installation, including fasteners and accessories, are onsite before commencing installation.

14.3.1 Unloading 

Set out a flat area and supporting dunnage to ensure sheets will not be damaged by site debris.

When unloading by crane, ensure the lifting boom has a spreader bar and that tightening strops do not damage sheet laps. Slings or strops should be nylon with leather sleeves to prevent fraying or cutting and damaging slings. Single slings and chains should not be used to lift packs of cladding.



When unloading by hand, lift each sheet off the stack without sliding over under sheets, as that may cause damage to the paint.

The person receiving the roof is responsible for identifying a safe and convenient landing point for the load, in association with the main contractor. The mobile or truck mounted crane operator has the duty of declining any loading instruction which he deems unsafe. Under no conditions should the load be traversed directly above any person

Bundles or packs of roof cladding must remain banded when being lifted by a crane.
They must be placed adjacent to the portal frame and not mid-span on the purlins. Bundles must be placed so that their weight is spread over the entire area of the roof and should be positioned with the laps in the direction of laying.
Workers receiving a bundle of roof cladding on the roof must have sufficient mobility to avoid the load, and use tag lines to control the swinging of the load while it is out of reach.
Packs must be securely fixed to the structure.

14.3.2 Wet Storage Damage 

Close stacked sheets may deteriorate quickly if water enters the pack. This happens because the metal exposed to moisture without air forms bulky, unstable, and loosely adherent, hygroscopic compounds. See 4.10.7 Crevice Corrosion/Wet Storage Stain.

Water can infiltrate deeply into a bundle of close-stacked sheets. The extent and severity of wet storage stain is usually proportional to the time the sheeting has been wet, however, the time to onset can be very variable, and occur more rapidly in warm conditions. 

Sheets can be dried by filleting sheets or cross-stacking them on a slope to allow water to drain and air to circulate between them. Only use a dry, well-ventilated environment for long-term storage.

A patchy visual appearance of the paint can also result from wet stack storage of pre-painted steel products. This is known as blooming.

Blooming results from water swelling the paint and flattening or suppressing gloss components. The gloss distortion is typically temporary and will dissipate with time, and exposure to heat/sunlight. This can be demonstrated by the application of boiling water to an affected surface bringing the appearance back to normal