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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 v24.12:Internal-Moisture; Insulation

Insulation

10.6 Insulation 

The increase in ceiling insulation standards helps prevent heat leakage into the ceiling space, but it does not affect the passage of water vapour. Ceiling insulation excludes more heat from the ceiling cavity, resulting in colder cavity air temperatures. Warmer air can hold more water vapour than cold air. Therefore, colder temperatures in the ceiling cavity lead to an increased risk of condensation.

Insulation Position

10.6.1 Insulation Position 

Insulation must be positioned so that there is a gap of at least 20 mm between insulation and roofing. On flat ceilings, or buildings without eaves, it must be placed so the gap is maintained at the eaves or an eaves insulation barrier should be fitted. To achieve this, an eaves insulation barrier may be required.

Other Insulation

10.6.2 Other Insulation 

Reflective foils are not defined as insulating, because they are only somewhat effective against radiative heat loss and have little impact on conductive and convective mechanisms. They also increase the potential for electrocution. As they are non-absorbent, they are not permitted as residential roofing underlay in New Zealand.

When Polyester blanket insulation is used in conjunction with metal roof cladding, special roofing screws should be used to avoid binding.

Composite insulated metal panels are described in 15.5 Warm Roofs.

Insulation must not be laid over the purlins as this compromises the air gap and the efficiency of the insulation where the roofing compresses it.