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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; 2019-May

19.20 2019 – May 

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

Important updates:

The main clause Roof Ventilation was renamed 10 Internal Moisture and completely revised and updated. The revised clause recommends designing and installing roof cladding to allow natural ventilation in residential buildings and requires design to enable ventilation in skillion, sarked, and low-pitched residential roofs.


Summary of other changes in this update

  • The main clause 14 Installation was revised and updated for clarity.
  • Some clauses from 13 Site Practice were moved to be included in the more relevant clause Installation. Site Practice now contains mainly 13 Safety.
  • Some clauses in 17 Testing were renamed and renumbered to fix broken links and reflect content more accurately. A major revision of 17 Testing is underway. 
  • Other changes are Category 1 updates, which fixed minor errata such as grammar, spelling, and layout.

19.20A Revision Detail - 2019 - May

CategoryClause Number (at time of update)Clause (As of current publication)Details
2 - Editing and rearrangement2.12.1 DefinitionsUpdated Glossary to include the terms: "Square Stopping".
2 - Editing and rearrangement3. Load DistributionMinor edit to drawing ( Deflection and the Square of Depth )
1 - Minor Errata3. Steel Purlins Edited for Consistency – changed 1.1 mm to 1 mm.
1 - Minor Errata4.14.1 NZBC Clause B2 (Extract)Revised for clarity.
1 - Minor Errata4. B2 ObjectiveReformatting
1 - Minor Errata4. B2 Functional RequirementsReformatting
1 - Minor Errata4. Performance RequirementsReformatting
2 - Editing and rearrangement4. Capillary ActionChanged minimum cover in 4.10.6B Roofing Sheet End Lap to closer reflect MRM recommendations and renamed the drawing.
1 - Minor Errata5. Method 2: Gutter and Downpipe Capacity Determined by CalculationsFixed broken link to E Standard Gutter Capacity and F Standard Down Pipe Capacity, and rewrote link copy for greater clarity.
2 - Editing and rearrangement8. Flashing ExpansionFirst line revised for clarity.
2 - Editing and rearrangement1010 Internal MoistureClause renamed to Internal Moisture.


Clause revised for clarity.


2 - Editing and rearrangement10.110.9 Minimising Ingress of Water Vapour into the Ceiling CavityClause renamed and revised for clarity.
4 - Clause Inserted10. E3 ObjectiveNew Clause
4 - Clause Inserted10. E3 Functional RequirementsNew Clause created
4 - Clause Inserted10.1.310.1.3 E3 Performance RequirementsNew clause created.
4 - Clause Inserted10.210.2 Why Manage Internal MoistureNewly created clause
2 - Editing and rearrangement10.410.3 Special RequirementsClause revised for clarity and relevance.
0 - Clause Removed10.410.4 The External EnvironmentClause removed, information has been revised and moved to other main clauses.
2 - Editing and rearrangement10.510.4 CondensationClause completely rewritten.
2 - Editing and rearrangement10.610.5 Building AirtightnessClause completely rewritten.
0 - Clause Removed10. Natural VentilationClause removed. New drawings used in more relevant clauses.
4 - Clause Inserted10.710.6 InsulationNewly created clause.
4 - Clause Inserted10. Insulation PositionNewly created clause
4 - Clause Inserted10. Other InsulationNewly created clause
0 - Clause Removed10. Direction of LayClause delted. Information is now discussed in Horizontal laying and Vertical laying.
0 - Clause Removed10.7.510.7.5 Non-Residential BuildingsClause removed. Information is discussed elsewhere.
2 - Editing and rearrangement10.810.7 ClimateClause revised for clarity.
0 - Clause Removed10.810.8 Wall UnderlayClause removed and content discussed i other relevant clauses.
4 - Clause Inserted10. HumidityRelative humidity (RH, given in per cent [%]), is the most widely known method: It gives the content of water vapour in the air relative to the maximum amount of water this parcel of air can hold at its present temperature.


Other measures are absolute humidity and water vapour pressure.

2 - Editing and rearrangement10.910.8 Moisture SourcesRenamed and revised clause for clarity. Lead clause for various "Sources of Internal Moisture"
4 - Clause Inserted10. Occupant BehaviourNewly created clause, combining new information with some from revised "Managing Water Vapout at the Source" (renamed Sources of Internal Moisture).
4 - Clause Inserted10. HeatingNewly created clause
2 - Editing and rearrangement10.9.410.8.4 Construction MoistureClause revised for clarity.
4 - Clause Inserted10.9.510.8.5 Ground MoistureNewly created clause
2 - Editing and rearrangement10.1110.10 Ventilation PathwaysClause revised for clarity.
4 - Clause Inserted10. Methods of VentilationNewly created clause
4 - Clause Inserted10. Soffit VentsNewly created clause.
4 - Clause Inserted10. Fascia VentsNewly created clause
4 - Clause Inserted10.11.1.310.10.1.3 Ridge VentsClause renamed and revised for clarity.
2 - Editing and rearrangement10.11.1.410.10.1.5 Turbine VentsClause revised for clarity.
4 - Clause Inserted10. BattensNewly Created clause.
2 - Editing and rearrangement10.1210.11 UnderlayClause revised and expanded for clarity.
4 - Clause Inserted10. Underlay RequirementsNewly created clause.
2 - Editing and rearrangement10. Types Of UnderlayClause revised for clarity.
4 - Clause Inserted10.12.310.11.3 Underlay UsageClause revised for clarity.
2 - Editing and rearrangement10.12.410.11.4 Underlay DurabilityClause revised and expanded.
2 - Editing and rearrangement10.12.510.11.5 Installing UnderlayClause revised and expanded.
4 - Clause Inserted10. Horizontal LayingNewly created clause.
4 - Clause Inserted10. Vertical LayingNewly created clause.
2 - Editing and rearrangement10.12.5.310.11.5.3 Underlay SupportClause revised.
2 - Editing and rearrangement10.1310.12 Additional InformationClause renamed to Additional Information.
2 - Editing and rearrangement10. Cold RoofsClause revied for clarity.
2 - Editing and rearrangement10. Warm RoofsClause revised for clarity.
2 - Editing and rearrangement10.13.310.12.3 Night Sky RadiationClause revised for clarity.
2 - Editing and rearrangement10.13.410.12.4 The Mechanics of CondensationClause revised and renamed, it is now: The Mechanics of Condesation.
4 - Clause Inserted10.13.510.12.5 Underlay StandardsNewly created clause.
4 - Clause Inserted10.13.610.12.6 Relative HumidityNewly created clause
4 - Clause Inserted10.13.710.12.7 Absolute HumidityNewly created clause
4 - Clause Inserted10.13.810.12.8 Water Vapour PressureNewly created clause
2 - Editing and rearrangement13.213.1.13 Roof Access During ConstructionClause movved to 13 Safety
0 - Clause Removed13.413.4 Acceptance Of Materialsclass="views-field views-field-field-revision-message-revision-id">
0 - Clause Removed13. Presence Of Moisture Between SheetsClause combined with 14.3.2 Wet Storage Damage
0 - Clause Removed13. Colour MatchClause combined with 14.19.5 Colour Matching Paint
0 - Clause Removed13.4.313.4.3 Storage StainClause removed.
0 - Clause Removed13.513.5 Roof LoadingClause combined with 14.3.1 Unloading
2 - Editing and rearrangement1414 InstallationClause revised for clarity.
2 - Editing and rearrangement14.114.1 Pre- InstallationClause revised for clarity.
2 - Editing and rearrangement14.114.11 OverhangClause revised for clarity
0 - Clause Removed14.114.10 Metal Roof DefectsClause removed. See 14.19.1 Roof Cladding Damage
0 - Clause Removed14.1.514.1.5 Cutting And DrillingClause deleted. Information was spread through other clauses, mainly Repairing Swarf Damage
4 - Clause Inserted14.214.2 Product SelectionNewly Created Clause
2 - Editing and rearrangement14.214.21 CompletionClause revised for clarity.
4 - Clause Inserted14. MeasuringNewly created clause
0 - Clause Removed14. Swarf Removalclause removed, subject is now discussed in Preventing Swarf Damage.
4 - Clause Inserted14. OrderingNewly created clause.
2 - Editing and rearrangement14.2.314.2.3 TransportationClause revised for clarity and moved to 14 Installation.
4 - Clause Inserted14.314.3 Accepting DeliveryNew created clause, combining Acceptance of Materials, previously in Site Practice.
4 - Clause Inserted14. UnloadingNewly created clause
0 - Clause Removed14. Primary FastenersClause removed. Information is now discussed in various shorter and newly created clauses.
4 - Clause Inserted14. Wet Storage DamageNewly created clause
014.414.4 Secondary Fastenersclass="views-field views-field-field-revision-message-revision-id">
0 - Clause Removed14. Monel Rivetsclause removed, information is now discussed in other clauses.
0 - Clause Removed14.4.314.4.3 Aluminium RivetsClause removed, information now in 14.13.4 Rivets
0 - Clause Removed14.4.414.4.4 Stainless Steel RivetsClause deleted. See 14.13.4 Rivets
0 - Clause Removed14.4.614.4.6 Fastener FrequencyClause removed. See 14.14.1 Fastener Spacing
2 - Editing and rearrangement14.514.5 HandlingClause revised for clarity and moved to Installation.
0 - Clause Removed14. Pan FixingClause Removed. See 14.13.2 Screws
0 - Clause Removed14.5.314.5.3 Expansion FixingsClause removed. See 14.14.4 Fastener Allowance for Expansion
0 - Clause Removed14.5.414.5.4 Lap StitchingClause removed. Information absorbed in other clauses.
2 - Editing and rearrangement14.614.6 Walking On RoofsClause revised for clarity and moved to 14 Installation.
0 - Clause Removed14.614.6 InstallationEmpty heading removed. See 14.14 Fastener Installation.
4 - Clause Inserted14. FootwearNewly created clause
2 - Editing and rearrangement14.714.7 Strippable FilmsClause revied for clarity.
0 - Clause Removed14.714.7 Re-RoofingClause removed. Information absorbed in other clauses.
4 - Clause Inserted14. Storing Product with Strippable FilmNewly created clause
2 - Editing and rearrangement14.814.9 Setting Out Clause revised for clarity.
0 - Clause Removed14. Side Lap Fixing Between PurlinsClause removed.
0 - Clause Removed14.8.614.8.6 Purlin Protectionclause removed
0 - Clause Removed14.8.714.8.7 DrainageClause removed
0 - Clause Removed14.8.814.8.8 CondensationClause removed.
4 - Clause Inserted14.914.10 Marking and CuttingNewly created clause
2 - Editing and rearrangement14.1114.12 Sealing and JoiningClause revised for clarity
4 - Clause Inserted14. Sealing End LapsNewly created clause
2 - Editing and rearrangement14.1214.13 FastenersClause revised for clarity. Nailsclass="views-field views-field-field-revision-message-revision-id">
2 - Editing and rearrangement14. ScrewsClause revised for clarity.
4 - Clause Inserted14.12.314.13.3 Clip FastenersNewly created clause.
2 - Editing and rearrangement14.12.414.13.4 RivetsClause revised for clarity
2 - Editing and rearrangement14.1314.14 Fastener InstallationClause renamed and revised for clarity.
2 - Editing and rearrangement14. Fastener SpacingNewly created clause
4 - Clause Inserted14. Fastener PlacementNewly created clause
4 - Clause Inserted14.13.314.14.3 Fastener SeatingNewly created clause
4 - Clause Inserted14.13.414.14.4 Fastener Allowance for ExpansionNewly created clause
4 - Clause Inserted14.1414.15 Modes Of Fastener FailureClause revised for clarity
4 - Clause Inserted14.1514.16 Stop-endsClause revised for clarity.
2 - Editing and rearrangement14.1614.17 Turndowns (Drip Forming or Drip Edging) Clause revised for clarity.
4 - Clause Inserted14.1714.18 Soft edging and FlashingNewly created clause
4 - Clause Inserted14.1814.19 Avoiding ProblemsNewly created clause heading
2 - Editing and rearrangement14. Roof Cladding DamageClause revised for clarity and moved to 14 Installation
4 - Clause Inserted14. Water PondingNewly created clause
4 - Clause Inserted14.18.314.19.3 Correctly Installed GuttersNewly created clause
014.18.414.19.4 Swarf Damageclass="views-field views-field-field-revision-message-revision-id">
4 - Clause Inserted14. Identifying Swarf StainsNewly created clause
4 - Clause Inserted14. Preventing Swarf DamageNewly created clause
4 - Clause Inserted14.18.4.314.18.4.3 Swarf Effect on PerformanceNewly created clause.
2 - Editing and rearrangement14.18.4.414.18.4.4 Repairing Swarf DamageClause revised for clarity and renamed.
4 - Clause Inserted14.18.4.514.19.4.2 Severe or Extensive Swarf StainingNewly created clause.
4 - Clause Inserted14.18.514.19.5 Colour Matching PaintNewly created clause
4 - Clause Inserted14.18.614.19.6 Field PaintingNewly created clause.
4 - Clause Inserted14.18.714.19.7 SunscreenNewly created clause.
4 - Clause Inserted14.18.814.18.8 Removing LichenNewly created clause.
2 - Editing and rearrangement14.2114.22 Tools Of The TradeClaused revised for clarity.
4 - Clause Inserted14. SpacingClause removed. See 14.14.1 Fastener Spacing
4 - Clause Inserted14. Crest FixingClause removed. See 14.13.2 Screws
4 - Clause Inserted14.2314.6.2 ToolsClause removed. See 14.13.2 Screws
4 - Clause Inserted14.2414.8 Translucent SheetingClause removed.
4 - Clause Inserted14. Side-Lap FixingClause removed.
4 - Clause Inserted14. End LapsClause deleted.
4 - Clause Inserted14.24.314.8.4 Midspan SupportsClause removed
4 - Clause Inserted14.24.414.8.5 StopendsClause removed.
4 - Clause Inserted14.24.514.8.9 PitchClause removed.
2 - Editing and rearrangement1717 TestingEdited for clarity.
2 - Editing and rearrangement17.117.1 ScopeClause revised for clarity
1 - Minor Errata17. Resistance to point loadFixed typos – "serviceability" and "strength".
2 - Editing and rearrangement17.217.2 Background to ScopeHeading changed from "Commentary on 16.1" and clause revised for clarity and brevity.
4 - Clause Inserted17.417.4 Commentary On 16.3Clause removed
2 - Editing and rearrangement17.517.5 Determining Wind load Span GraphsMinor grammatical edits and clause renamed to "Determining Wind Load Span Graphs" to avoid confusion with 3.11.1 Steel Cladding Wind Load Span Graphs.
1 - Minor Errata17.617.6 Specific Methods Of Testing Sheet Roof And Wall CladdingClause moved (renumbered) to follow 17.7 Wind and Point Load Testing.
4 - Clause Inserted17. Commentary On Section 15.5Clause Removed. 17 Testing to undergo major revision.
2 - Editing and rearrangement17.917.9 Background to wind load testingRenamed "Clause from Commentary on 16.6".