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Disclaimer

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.

Scope

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:Structure; Standards

3.2 Standards 

Roof and wall cladding must structurally comply with the performance requirements of NZBC Clause B1 Structure. Loads may be calculated in accordance with AS/NZS 1170 (Loadings Standard), and these loads are used to develop prescriptive solutions such are found in NZS 3604 Timber Framed Buildings and NASH Standard for Light Steel Framed Buildings. 

3.2.1 AS/AZS 1170.2:2011 

Designers should be familiar with the current Loadings Code, including amendments. Manufacturers' printed technical literature, using different criteria or test values and superseded Standards can information that is not compatible with the latest requirements.

The Loadings Code identifies four load categories relevant to metal roof and wall cladding.

  • Wind actions:
  • Wind imposed inwards forces (pressure) where the wind is slowed, and outward pressures (suction) where the wind accelerates. The shape of the structure induces local pressure factors where pressure is concentrated. Internal pressures may also be generated within a building.
  • Permanent action:
    Dead load is the permanent weight of the roof structure and the permanent part of an imposed load, such as an air conditioning unit.
  • Imposed action:
    Live loads are variable loads imposed on the building by its occupants and contents, such as a person standing on the roof (point load).
  • Induced actions:
    Loads such as wind, snow or ice, and ponding rainwater.

When a structure, or part of it, fails to fulfil its expected basic functions, it is said to have reached a limit state; the two limit states are Serviceability Failure and Ultimate Failure. (see 3.7 Modes of Failure.)

3.2.2 NZS 3604:2011 

NZS 3604 Timber Framed Buildings  is an acceptable solution to comply with the NZBC for light timber frame buildings not requiring specific design.

It contains prescriptive dimensions for purlin spacing and fasteners, based on maximum design wind speeds of Low (32 m/s), Medium (37 m/s), High (44 m/s), Very High (50 m/s), or Extra High (55 m/s). The load calculations for NZS3604 were based on a simplified interpretation of AS/NZS 1170.  These values can be used for calculation of loads on the cladding of structures designed using NZS 3604.

NZS 3604 includes:

  • Timber frame construction.
  • Height from lowest ground to the highest point on the roof may not exceed 10 m.
  • A snow load may not exceed 1.0 kPa, although Section 15 of NZS 3604 does provide additional criteria for 1.5 kPa and 2.0 kPa snow loads.

NZS 3604 excludes:

  • buildings dedicated to the preservation of human life;
  • buildings which may host crowds;
  • publicly owned buildings containing high value contents; and
  • curved roof construction.

Because the buildings covered by this standard are limited in size, wind loads include a local pressure factor of 1.5 kPa over the entire structure, rather than varying factors according to the position on the roof as required by AS/NZS 1170.2:2011.

3.2.3 NASH Standard 

Nash Standard Part 2 is cited in B1/AS1 as an Acceptable Solution for light steel framed buildings within a scope similar to that of NZS 3604