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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:Structure; Fasteners

3.8 Fasteners 

Most fastener failures happen due to negative load (or uplift) resulting in pull out of the screw from the support, or the screw pulling through the cladding or causing permanent deformation. Testing procedures are designed to closely simulate these conditions.

Product testing does not include pull-out of the screw, this should be checked independently.

3.8.1 Fastener Loads 

Fastener failure by fatigue can occur when fasteners embedded in timber or hot rolled steel, are subject to frequent bending action by repeated thermal expansion forces. This is unlikely to happen to cold rolled steel purlins up to 2.5 mm in thickness as the thinner depth of connection of the screw into the purlin allows it to rotate, rather than bend.



3.8.2 Steel Purlins  

A fastener penetration of three threads through the steel member is sufficient for the fastener to meet its full design capacity.  Pull-out failure of screws must be checked when assessing a profile's load/span capacity.

The pull-out values of screws into light gauge steel battens or purlins varies greatly with thread design, pitch, and drill point shape. When fastening into light gauge steel, the pull-out values of the specified screw must be considered, and the installation must be completed with that type, gauge, and brand of screw. In light gauge steel under 1mm in thickness, it is also important to avoid stripping out the formed screw thread

3.8.3 Timber Purlins 

Timber purlins generally require a fastener penetration of 30 mm. With this level of embedment, a screw equipped with a profiled washer though 0.55 material will fail by pull-through of the cladding before it fails by fastener withdrawal from the timber. Greater thicknesses of cladding may require specific design. For fastening into sarking or rigid air barrier less than 30 mm thick, the pull-out values for the specific screw and sarking material should be obtained from the supplier and required fastener pattern calculated.

3.8.4 Pull-over Values 

Pull-over values for medium and high rib trapezoidal profiles must be checked against strength loads provided by testing.

Pull-over load depends on the head or washer size. For example, as 12# and 14# screw heads have approximately the same diameter, these screw sizes have the same design load value for pull-over. If the pullover load is likely to be exceeded, the options are to increase the metal thickness or use a load-spreading washer.

3.8.5 Load-spreading Washers 

Profiled load-spreading washers spread high wind uplift-loads over a larger area around the fastener head. Using load spreading washers under the fastener can increase the load resistance of each fastener by up to 50%.

The type, size and stiffness of washers are critical for performance. Where performance data incorporating load-spreading washers is used, the specification of the washer must be quoted with the fastener.

In general, load-spreading washers should have a minimum thickness of 0.95 mm for steel and 1.2 mm for non-ferrous metal.



Where oversized holes are used to accommodate thermal movement of the sheeting, load-spreading washers should be used with sealing washers to ensure weather tightness.