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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 v25.06:Revision-History; V2506-June-2025

v25.06 June 2025

19.1 v25.06 June 2025

The update to the Code of Practice published on 1 June 2025 focused on clarification and usability.

Important Changes

We replaced the illustration for 9.4.2.6F Cricket Under-Soaker: Trapezoidal to show the width of the cricket flashing correctly.

In 8.8 Profile Closures, we removed a repeated paragraph and added illustrations showing vermin closures, and we removed a statement from 4.9.3 Compatibility with Non-Metallic Substances that neither AZ-coated steel nor Aluminium should be used as a flashing embedded in concrete or masonry.

In 8.10.1 Flashing Expansion, we clarified the required moisture content of timber and removed a recommendation for using aluminium rivets in place of expansion joints.

Other Notable Revisions

We renamed three clauses: 7.1.2 Runoff Capacity, 5.6 Outlets, and 5.7 Downpipes, with no changes to recommendations.

In another bid to improve clarity and usability, we introduced an interactive table to 16.7.1 Lichen And Mould. The table gives improved guidance on water/bleach ratios to achieve a 2% chlorine solution for treating lichen and mould on roofs.

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 v25.06 - 2025 - June

Category	Clause Number (prior to update)	Clause (As of current publication)	Details
3 - Substantial change to recommendation	4.9.3	4.9.3 Compatibility with Non-Metallic Substances	Removed statement that neither AZ coated steel nor aluminium should be used a a flashing embedded in concerete or masonry.
3 - Substantial change to recommendation	7.1.1	7.1.1 Minimum Roof Cladding Pitch	Added an exception to 7.1.1B Exceptions to the Minimum Recommended Roof Cladding Pitch requirements: regarding guidance for Reroofing trough section roofs at less than 3°.
3 - Substantial change to recommendation	8.10.1	8.10.1 Flashing Expansion	Clarified statement of the required moisture content of timber and removed statement about using aluminium rivets in place of expansion joints.
3 - Substantial change to recommendation	8.10.2	8.10.2 Building Expansion Joints	Corrected the slope of parapet cap from 10° to 3 – 5° and updated the illustrations to be consistent with the Code of Practice format.
3 - Substantial change to recommendation	16.7.1	16.7.1 Lichen And Mould	We introduced a new interactive table to assist in diluting Sodium Hypochlorite for use on roofs.
2 - Editing and rearrangement	1	1 Introduction	New revision message for v25.03, published on 1 March 2025.
1 - Minor Errata	1.5.2	1.5.2 Adjudication	Minor typo fix: and to an. No change to recommendations.
1 - Minor Errata	4.3	4.3 Metal Performance	Typo fix in 4.3A Metal Performance in Acid/Alkaline Environments, updated font in illustration—no changes to recommendations.
1 - Minor Errata	4.4.1	4.4.1 Sacrificial Protection	Typo fix: zinc-oxide to zinc oxide. No changes to recommendations.
1 - Minor Errata	4.5.2	4.5.2 Sea Spray	Minor for clarity and a typo fix. No changes to recommendations.
1 - Minor Errata	4.7.1	4.7.1 West Coast of the South Island and South Coast of the North Island	Edited the clause heading for clarity. No changes to recommendations.
1 - Minor Errata	4.9.4	4.9.4 Compatibility Table	Typo fix/ Changed prepainted Aluminium to Pre-Painted Aluminium.
1 - Minor Errata	4.10.1	4.10.1 Unwashed Areas	Edit for style, grammar, clarity, and consistency.
1 - Minor Errata	4.10.2	4.10.2 Poultice Corrosion	Punctuation fix: eg to e.g., No change to recommendations.
1 - Minor Errata	4.10.3	4.10.3 Solar Collectors and Other Roof Mounted Structures	Some punctuation and typo fixes. No changes to recommendations.
1 - Minor Errata	4.10.6	4.10.6 Capillary Action	Removed repeated sentence. No changes to recommendations.
1 - Minor Errata	4.11	4.11 Inert Catchment	Added some labels for clarification to 4.11A Localised Damage due to Inert Catchment.
1 - Minor Errata	4.14	4.14 Swarf Staining and Cut Edge Corrosion	Grammar Fix. No changes to recommendations.
1 - Minor Errata	4.15	4.15 Clearances	Illustration reformatting. No changes to recommendations.
1 - Minor Errata	4.15.1	4.15.1 Ground Clearance	Illustration reformatting. No changes to recommendations.
1 - Minor Errata	5.3.2.1	5.3.2.1 Designing for Climate Change	Table fomatting for 5.3.2.1A RCP Level Descriptions. No change to content or recommendations.
1 - Minor Errata	5.3.2.3	5.3.2.3 Allowance for Short-Term Intensities	Punctuation Fix. No change to content or recommendations.
1 - Minor Errata	5.4	5.4 Gutters	Grammar fix. No change to content or recommendations.
1 - Minor Errata	5.4.1	5.4.1 External Gutters (Spouting)	Grammar fix.
1 - Minor Errata	5.4.5	5.4.5 Internal Gutters	Font sizing in 5.4.5A Separation of Butyl Gutter and Metal Roofing. No change to content or recommendations.
1 - Minor Errata	5.4.7	5.4.7 Gutter Capacity Calculator	Typo fix. No change to content or recommendations. The enforced minimum remains unchanged at 2.2.
1 - Minor Errata	5.5.2	5.5.2 Valley Design	Typo fix. No change to content or recommendations.
1 - Minor Errata	5.5.4	5.5.4 Intersecting Valleys	Font resizing in 5.5.4A Correct Valley Intersection and 5.5.4B Incorrect Valley Intersection. No change to content or recommendations.
2 - Editing and rearrangement	5.5.5	5.5.5 Changing Angles in Valleys	Added an illustration showing the details for changing angles or pitch in valleys.
2 - Editing and rearrangement	5.6	5.6 Outlets	The clause was renamed, and some content from 5.7 Downpipesrelating to Outlets was moved to this clause. No changes to recommendations.
2 - Editing and rearrangement	5.7	5.7 Downpipes	This clause was renamed, and some content was moved to 5.6 Outlets. Minor edit for clarity: removed the reference to astragalus. No other changes to content or recommendations.
2 - Editing and rearrangement	5.8.1	5.8.1 Maximum Area Above Spreader Calculator	Updated casing of labels for consistency
2 - Editing and rearrangement	6	6 External Moisture Overview	Minor edit for clarity. No changes to recommendations.
1 - Minor Errata	6.3	6.3 Related Topics	Punctuation fix. No change to content or recommendations.
2 - Editing and rearrangement	7.1.2	7.1.2 Runoff Capacity	Renamed the clause 7.1.2 Runoff Capacity for clarity. No changes to recommendations.
1 - Minor Errata	7.1.3	7.1.3 Roof Drainage Capacity	Font display fixed in 7.1.3A Trough Capacity and 7.1.3B Penetration Gutters. No other changes to content or recommendations.
1 - Minor Errata	7.3.2	7.3.2 Roof Cladding Expansion Provisions	Font resized for 7.3.2A Favourable Circumstances for Controlling Expansion and 7.3.2B Unfavourable Circumstances for Controlling Expansion. No changes to recommendations.
1 - Minor Errata	8.1	8.10 Flashing Expansion Details	Some grammar fixes and removed optional Caption tags from illustrations. No changes to recommendations.
1 - Minor Errata	8.4	8.4 Flashing Cover	Typo fix. No change to content or recommendations.
1 - Minor Errata	8.4.1	8.4.1 Apron Upstands	Typo fix in 8.4.1A Undertray for an Additional Upstand. No changes to content or recommendations.
1 - Minor Errata	8.4.4	8.4.4 Flashing Laps	Typo fix. No other changes.
0 - Clause Removed	8.5.2	Head Barge/Ridge/Barge Junction	Clause removed because it was a double-up. 8.5.2.1D Head-Barge/Ridge/Barge Junction is still available under 8.5.2.1 Ridge – barge Intersections.
1 - Minor Errata	8.5.4	8.5.3 Parapet Cappings	Typo in title of 8.5.3A Parapet Cap Expansion Provisions and font updates in the other illustrations.
1 - Minor Errata	8.5.5.1	8.5.4.1 Parapet And Apron Capping Terminations	Typo fix, changed and to an, and deleted the optional caption tag from illustrations. No other changes.
1 - Minor Errata	8.9	8.9 Compression Timber	Grammar fix. Removed redundant word. No other changes.
1 - Minor Errata	9.5.2.2	9.5.2.2 Mechanical Services	Removed Optional Caption tag from below the illustrations.
1 - Minor Errata	9.5.3	9.5.3 Flush Penetrations	Grammar fix.
1 - Minor Errata	11.6	11.6 Installing Translucent Sheets	Fixed typo and text formatting in 11.6B Translucent Sheet Stop End. No changes to recommendations.
4 - Clause Inserted		19.1 v25.06 June 2025	Revision details for the 1 June 2025 update.