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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 v26.06:Revision-History; V2606-June-2026

19.1 v26.06 June 2026 

Substantial changes to recommendations

  • The 5.7.3 Downpipe Capacity Calculator and 5.7.2A Downpipe Capacity Table have been updated with common dropper sizes, which resulted in a decrease in downpipe capacity in many cases. The calculator now automatically selects the minimum dropper size relevant to a chosen downpipe size.
  • The calculations in the 9.4.4 Maximum Area Above Penetration Calculator for corrugate profiles now assumes that there is no lap in the discharge trough. This resulted in an increase in the maximum area above penetrations recommendations in the CoP.
  • We improved general labelling and descriptions of conditions and dimensions for 5.5.6 Asymmetrical Valleys designs.
  • The clause 8.11 Wall Cladding now contains details for wall cladding flashings, including internal and external corners, and vermin proofing.
    Window details for Corrugate Horizontal on Cavity, Corrugate Vertical on Cavity, and Corrugate Vertical Direct fixed have been tested to comply with E2/VM1. Details are available from roofmattersnz@gmail.com and will be published the next Code of Practice revision on 1 September 2026.

Editing and rearrangement

 

19.1A Revision Detail v26.06 - 2026 - June

CategoryClause Number (prior to update)Clause (As of current publication)Details
2 - Editing and rearrangement11 IntroductionNew revision message for v26.06, published on 1 June 2026.
2- Editing and rearrangement 5.7.2 Capacity Table for Common Size DownpipesRevised the 5.7.2A Downpipe Capacity Table to use dropper sizes and linked the table to the 5.7.3 Downpipe Capacity Calculator.
1 - Minor Errata 4.6.3 Material SelectionFixed table content alignment.
3 - Substantial change to recommendation 5.4.6 Secret GuttersRevised 5.4.6B Secret Gutter Detail to clearly show the height of the gutter.
1 - Minor Errata 5.4.7 Gutter Capacity CalculatorGrammar fix.
2 - Editing and rearrangement 5.5.6 Asymmetrical ValleysAdded clarification for asymmetrical valley dimensions.
 
3 - Substantial change to recommendation 5.5.7 Valley Capacity CalculatorImprove labeling and conditions for asymmetrical valley designs and fix label positioning.
Clarifies requirement for valley baffle in some asymmetrical designs.
1 - Minor Errata 5.6 OutletsCorrection for clarity.
1 - Minor Errata 5.7.2 Capacity Table for Common Size DownpipesFixed link to 5.7.3 Downpipe Capacity Calculator
3 - Substantial change to recommendation 5.7.3 Downpipe Capacity CalculatorUpdated for in-place selection of common downpipe sizes, and now uses measured dimensions of standard droppers.
This may result in reduced capacity vs previous calculations.
2 - Editing and rearrangement 5.8.1 Maximum Area Above Spreader CalculatorGrammar fix and additional callout on illustration to Condition 3
1 - Minor Errata 7.1.4 Maximum Run CalculatorGrammar fix.
2 - Editing and rearrangement 7.3.2 Roof Cladding Expansion ProvisionsRevised 7.3.2A Favourable Circumstances for Controlling Expansion to show the correct recommendations for aluminium.
1 - Minor Errata 8.4 Flashing CoverRemoved requirement for a baffle in Category C in 19.1A Revision Detail v26.06 - 2026 - June.
2 - Editing and rearrangement 8.8 Profile ClosuresIllustrations for vermin flashings have been moved to 8.11 Wall Cladding.
3 - Substantial change to recommendation 8.11 Wall CladdingRenamed clause and added illustrations for wall cladding flashings and vermin closures.
3 - Substantial change to recommendation 9.4.4 Maximum Area Above Penetration CalculatorFor corrugate profiles this now assumes flow to top of profile (no freeboard), which increases area but requires that there be no discharge to lap row.
2 - Editing and rearrangement 10.10.1.2 Fascia VentsThis clause has been revised as part of the larger revision of 10.10 Ventilation Pathways.
2 - Editing and rearrangement 10.10.2 BattensEditing of 10.10.2B Ventilation Pathway: Top Plate with Underlay to clearly show a baffle.
1 - Minor Errata 14.10 OverhangEdit for clarity. No changes to recommendations.
1 - Minor Errata 17.1.3.1 UDL TestingMinor edit for clarity.
2 - Editing and rearrangement 17.2 MRM Fastener Performance Requirements and TestingAdded recommendation fastener identification stamped on the head.
2 - Editing and rearrangement 19 Revision HistoryPDF Download of the Code of Practice now contains detailed revision history for only changes made to the current edition
1 - Minor Errata 19.2 April 2026Correction to clause links
4 - Clause Inserted 19.1 v26.06 June 2026Latest revision.