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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 v24.06:Revision-History; 2021-March

19.13 2021 – March 

The addition of an interactive calculator for asymmetrical valleys constitutes the most important inclusion in this update.

The other capacity calculators have all been refined and positioned for improved usability.

In addition, various drawings have been updated for accuracy and correctness.

The rest of this update consisted of fixing minor errors and improvements for clarity.


19.13B Revision Detail - 2021 - March

CategoryClause Number (at time of update)Clause (As of current publication)Details
2 - Editing and rearrangement11 IntroductionUpdate Revisions Message
1 - Minor Errata2.12.1 DefinitionsAdded definitions for Translucent, Transparent, Opalescent, and Opaque.
1 - Minor Errata3.133.4.5 Material GradeMinor revision for Aluminium.
0 - Clause Removed4.8Biological CorrosionClause removed. 4.8.4 Lichen is now in 4.8 Paint Durability, and 4.10.9 Gutter Leaf Guard is now in 4.10 Other Causes of Corrosion.
2 - Editing and rearrangement5. Valley Capacity CalculatorUpdated calculator to support Asymmetrical Valley calculations, including dynamic illustration.
2 - Editing and rearrangement5. Maximum Area Above Spreader CalculatorClause edited, new clause (Downpipe Spreaders) introduced with explanatory text about spreaders. Trapezoidal illustration updated to show effective pan-depth area.
2 - Editing and rearrangement5.65.4.2 Gutter Capacity DesignClause renamed and moved to Types of Gutter.  
1 - Minor Errata5. Spouting Support SystemsClause moved to Gutter Installation and Maintenance.
2 - Editing and rearrangement5.6.314.18.9 Gutter InstallationClause renamed and moved to Pre-empting Problems.
2 - Editing and rearrangement5.7.15.8 Downpipe SpreadersPreviously removed clause, now reinstated and updated to align with the new Maximum Area Above Spreader Calculator.
1 - Minor Errata5. Gutter FallClause moved to Gutter Installation and Maintenance.
2 - Editing and rearrangement5. Downpipe Capacity CalculatorIllustration updated to show effective head.
2 - Editing and rearrangement5.85.4.7 Gutter Capacity CalculatorRectangular Gutter illustration updated to show effective gutter area. Clause renamed to refine search results.
0 - Clause Removed6.2Acceptable Solution NZBC E2/AS1Clause removed as it pertains to E2, which is discussed in NZBC Clause E2 External Moisture (Extract).
2 - Editing and rearrangement6.2.16.2 ComplianceClause promoted, replacing ES/AS1 at postion 6.2, and content of clause reviewed.
2 - Editing and rearrangement7. Maximum Run CalculatorTrapezoidal illustration updated to show effective pan-depth area.
2 - Editing and rearrangement7.47.4 End LapsDrawing deleted, replaced with a reference to 14.12.1 Sealing End Laps.
2 - Editing and rearrangement8.78.8 Profile ClosuresClause revised. Recommendations have not changed. Drawings replaced with more accurate depictions.
2 - Editing and rearrangement9. Maximum Area Above Penetration CalculatorTrapezoidal illustration updated to show effective pan-depth area.
2 - Editing and rearrangement14. Sealing End LapsDrawing replaced with with more accurate depiction of correctly and incorrectly sealed end laps.
1 - Minor Errata15. SubstrateRemoved empty link.
4 - Clause Inserted 19.13 2021 – MarchNew Revision clause.