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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 v23.09:Revision-History; 2019-December

19.15 2019 – December 

The following updates to the NZ Metal Roof and Wall Cladding Code Practice (COP), are effective 1 December 2019.

Major Revisions

  1. For this update, the COP section 5 Roof Drainage and all its sub-clauses have been substantially revised. The updates focussed heavily on creating new online tools for calculating Roof Drainage, Gutter Capacity, Downpipe Capacity and Valley Capacity, which are located in 5.4.7 Gutter Capacity Calculator.

Summary of other changes in this update

19.15A Revision Detail - 2019 - December

CategoryClause Number (at time of update)Clause (As of current publication)Details
2 - Editing and rearrangement11 IntroductionUpdate Revisions Message
2 - Editing and rearrangement2.12.1 DefinitionsRevised definition of "Load Spreading Washer", added a new item "Profiled Washer", added definition for "Finial",  minor grammatical fixes.
2 - Editing and rearrangement55 Roof Drainage The entire Roof Drainage-clause had been revised.
1 - Minor Errata5.15.1 NZBC: Clause E1 — Surface WaterFormatting
4 - Clause Inserted 5.4 GuttersNew clause.
4 - Clause Inserted 5.4.1 External Gutters (Spouting)New clause.
2 - Editing and rearrangement5. Concealed Fascia GuttersThis clause had been completely revised and renamed.
2 - Editing and rearrangement5. Internal GuttersClause completely revised.
4 - Clause Inserted Internal Gutter Design FeaturesNew clause.
2 - Editing and rearrangement5.65.5 Valleys  Valleys had been completely revised and divided into smaller, more specific, sections.
4 - Clause Inserted 5.5.1 Valley FixingNew clause.
4 - Clause Inserted 5.5.2 Valley DesignNew clause.
4 - Clause Inserted 5.4.3 Internal CornersNew clause.
2 - Editing and rearrangement5. Bifurcated ValleysThe clause had been revised. Valleys are now discussed in smaller, more specific, clauses.
4 - Clause Inserted 5.5.5 Changing Angles in ValleysNew clause.
4 - Clause Inserted 5.5.6 Asymmetrical ValleysNew clause.
4 - Clause Inserted 7.1.3 Roof Drainage CapacityNew clause.
3 - Substantial change to recommendation5. Secret GuttersClause revised, for brevity and clarity.
4 - Clause Inserted 5.6 Rainwater Heads, Sumps, and OverflowsNew clause.
2 - Editing and rearrangement5. Rainwater HeadsClause revised, now providing more information.
2 - Editing and rearrangement5.85.6.2 SumpsThis clause has been revised.
2 - Editing and rearrangement5. OverflowsClause renamed, Outlets are now discussed under Outlets and Downpipes.
4 - Clause Inserted 5.7 Outlets and DownpipesNew clause.
4 - Clause Inserted 5.7.1 Placement of DownpipesNew clause.
4 - Clause Inserted 5.7.2 Capacity Table for Common Size DownpipesNew clause.
2 - Editing and rearrangement5. Gutter Capacity DesignClause has been revised and edited.
4 - Clause Inserted Maximum Gutter LengthNew clause.
2 - Editing and rearrangement5. Gutter Support SystemsClause revised.
4 - Clause Inserted 14.18.9 Gutter InstallationNew clause.
2 - Editing and rearrangement5.25.3 Roof Drainage DesignClause had been completely revised.
2 - Editing and rearrangement5. Catchment AreaCaluse has been completely revised. All calculations are now under a new clause Capacity Calculations.
2 - Editing and rearrangement5. Gutter FallClause revised and renamed.
3 - Substantial change to recommendation5.35.3.2 Rainfall IntensityClause had been completely revised, with updated Rainfall Intensity Maps at the end of the main Clause, Roof Drainage. 
4 - Clause Inserted Allowance for Short-Term IntensitiesNew clause.
4 - Clause Inserted DurationNew clause
2 - Editing and rearrangement5. Gutter Capacity CalculatorThe old clause, Capacity Calculations, replaced by a new clause of the same name but including new online tools.
4 - Clause Inserted 5.7.1 North Island 50-year ARI, 10-minute Rainfall Intensity MapNew clause.
4 - Clause Inserted 5.7.2 South Island 50-year ARI, 10-minute Rainfall Intensity MapNew clause.
4 - Clause Inserted8.38.4 Flashing CoverAdjusted spacing in Table 8.3A
2 - Editing and rearrangement8. Step ApronRemoved reference to "Fortress Fasteners" in drawing A:  Step Apron Details.
4 - Clause Inserted8. Eaves FlashingDrawing renamed to Gutter Flashing.
2 - Editing and rearrangement12.212.2 Purlin CreasingInserted photograph.
4 - Clause Inserted17. Point Load Testing StandardNew Clause.
4 - Clause Inserted17. Point Load TestingNew clause.
1 - Minor Errata18.818.8 Sheet Metal Work For Roofing Contractors.Clause revised for gender neutrality. No significant changes.
4 - Clause Inserted 19.15 2019 – DecemberSummary of Changes – December 2019
0 - Clause Removed5.3.2.1Method 1: Gutter and Downpipe Capacity Determined by GraphThese methods have been replaced by online capacity calculating tools.
0 - Clause Removed5.3.2.3Method 2: Gutter and Downpipe Capacity Determined by CalculationsThese methods have been replaced by online capacity calculating tools.
0 - Clause Removed5.3.3Roof Cladding CapacityThese methods have been replaced by online capacity calculating tools.
0 - Clause Removed5.4SnowClause removed, Snow and hail are comprehensively discussed in Snow Loads.
0 - Clause Removed5.4.1HailClause removed. Leaf guards and maintenance are discussed under Gutter Maintenance.
0 - Clause Removed5.5GuttersThe clause had been removed. Gutters are now discussed in more detail in a separate clause for each type, under the main clause Types of Gutter.
0 - Clause Removed5.5.3Eaves GuttersClause deleted. Now discussed under External Gutters.
0 - Clause Removed5.6.1Valley CatchmentThis clause had been replaced with the newly developed online tool in Valley Capacity Calculations.
0 - Clause Removed5.7DownpipesInformation previously contained in this clause is now discussed in Outlets and Downpipes.
Out-of-band updates 16/12/2019
2 - Editing and rearrangement5.4.2A5.7.2 Capacity Table for Common Size DownpipesRemoved obsolete column for Roof Area Drained as the online calculator replaces this.
2 - Editing and rearrangement5.75.4.7 Gutter Capacity CalculatorAdded link to Common Sized Downpipes.