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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 v25.03:Revision-History; V2503-March-2025

19.1 v25.03 March 2025 

The updates published on 1 March 2025 mostly include some changes to recommendations and some editing and rearrangement for clarity and consistency.

Important Changes

We replaced the illustration for 8.5.1A Ridge-Hip Junctionas experience showed the extra line of defence previously shown is not required.

A new clarifying statement in 9.4.2.7 Cricket Over-Flashing More Than 1 m Wide gives guidance on when to use this detail rather than some of the under-soaker variants.

We changed 10.11.5 Underlay Durability to recommend specifying material strictly in accordance with the manufacturer’s recommendations when using synthetic underlay in unlined situations where it is exposed to fumes or reflected UV.

We've raised the 5.4.7 Gutter Capacity Calculator default Short-Term Intensity Multiplication Factor for Commercial Internal Gutters to 3.1 (from 2.2) for a more cautious design, while the minimum remains 2.2. This factor adjusts 10-minute rainfall figures for higher short-term intensities. Non-residential roofs now match the 3.1 default but can be adjusted down to 2.2 if needed.

Other Notable Revisions

We edited 3.11.2 Steel Cladding Wind Load Span Graphs and 3.11 Wind Load/Span Graphs – Designs to AS/NZS1170 to remove identical content in these two clauses. There were no changes to recommendations and no information was deleted. A new sub-clause gives guidance on  3.11.1 Fastener Pull-out in SED situations.

The 2 Glossary now has added definitions for dunnage, straps, and strops.

For Internal Moisture 10.1.4 Compliance, we added an improved explanation of the compliance requirements of NZBC E3.3a. We similarly introduced improved guidance to 14.8.5 Stopends to aid clarity, with no changes to recommendations.

In another bid to improve clarity, we replaced 'C1" and "C2" designations in  Minimum Flashing Cover with "X" and "Y" labels to reduce confusion.

In the 4.9.4 Compatibility Table, we revised the terminology for ZM Coated Steel to ZM/AM Coated Steel and moved Pre-Painted ZM/AM Coated Steel to be directly after ZM/AM Coated Steel to make the table more accurate and more easily interpreted.

The rest of the updates and revisions consisted of minor edits for clarity, grammar, and spelling. There were no other changes to recommendations.

19.1A Revision Detail v25.03 - 2025 - March

CategoryClause Number (prior to update)Clause (As of current publication)Details
2 - Editing and rearrangement11 IntroductionNew revision message for v25.03, published on 1 March 2025.
2 - Editing and rearrangement2.12.1 DefinitionsAdded definition for dunnage, straps, and strops.
2 - Editing and rearrangement3.113.11 Wind Load/Span Graphs – Designs to AS/NZS1170Revision of the introduction to remove repeated content. The rest of the content is still available in 3.11.2 Steel Cladding Wind Load Span Graphs.
2 - Editing and rearrangement3.11.13.11.2 Steel Cladding Wind Load Span GraphsEditing to address repeated content. The removed content is is still available in 3.11 Wind Load/Span Graphs – Designs to AS/NZS1170.
4 - Clause Inserted 3.11.1 Fastener Pull-outA new clause is giving guidance on fastener pullout in SED situations.
3 - Substantial change to recommendation4.9.44.9.4 Compatibility TableRevised ZM Coated Steel to ZM/AM Coated Steel and changed Pre-Painted Steel to Pre-Painted ZM/AM Coated Steel; moved Pre-Painted ZM/AM Coated Steel to be directly after ZM/AM Coated Steel.
3 - Substantial change to recommendation5.4.75.4.7 Gutter Capacity CalculatorUpdate the default Short-Term Intensity Multiplication Factor for Commercial Internal Gutters to 3.1 (from 2.2) as recommended for more prudent design.
The enforced minimum remains unchanged at 2.2.
1 - Minor Errata5.5.15.5.1 Valley FixingTypo fix. No changes to recommendations.
2 - Editing and rearrangement8.48.4 Flashing CoverReplaced 'C' and 'D' with 'X' and 'Y' to improve useability and extract Minimum Flashing Cover to a more visible level.
3 - Substantial change to recommendation8.5.18.5.1 Ridge and Hip IntersectionsReplaced illustration for 8.5.1A Ridge-Hip Junction as experience showed the extra line of defense is not required in these situations.
3 - Substantial change to recommendation9.4.2.79.4.2.7 Cricket Over-Flashing More Than 1 m WideAdded clarifying statement for use case of this detail, rather than other Undersoaker variants.
2 - Editing and rearrangement10.1.410.1.4 ComplianceWe added a more detailed explanation of NZBC, clause E3.3a requirements for compliance.
3 - Substantial change to recommendation10.11.510.11.5 Underlay DurabilityClause revised and expanded.
2 - Editing and rearrangement14.1614.15 Stop-endsImproved guidance for stop-ending cladding. No changes to recommendations.
1 - Minor Errata15.5.1.615.5.1.6 Insulation Panel Insulation ValuesDeleted an editorial comment, that was accidentally published. No changes to recommendations.
4 - Clause Inserted 19.1 v25.03 March 2025Revision details for the 1 March 2025 update.