The NZ Metal Roof and Wall Cladding Code of Practice

New Zealand's most authoritative resource for metal roofing and wall cladding

 

The latest changes to the NZMRM Metal Roof and Wall Cladding code of Practice were Published on 1 June 2026.

Substantial changes to recommendations

  • The 5.7.3 Downpipe Capacity Calculator and 5.4.2A 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

The Code of Practice provides a variety of interactive tools to simplify design tasks.

These include:

Roof Drainage Capacity Calculations

These provide a maximum allowable area that can be drained under various scenarios.

Material Compatibility

Provides an easy reference to compatibility for both contact and run-off between dissimilar materials.

Conversion Factors

Quick conversions between common (and not-so-common) units.

Pitch & Rise Calculator

Calculate pitch, fall or run, along with a reference table of valley fold angles.

The RANZ Roofing Guide developed by the Roofing Association of New Zealand in association with the NZMRM, provides detailed step-by-step, interactive 3D instructions for roof flashings, penetrations and wall cladding, with a particular focus on correct installation.

Works on desktops, laptops, tablets and phones.

Subscribe Now - Professional More information Subscription for NZMRM/RANZ members
Subscribe Now - Professional More information Subscription for NZMRM/RANZ members

It is recommended to refer to the Online Code of Practice wherever possible, as it is the most up-to-date, and includes tools which cannot be replicated in static printed form.

The COP is provided in PDF form for the purposes of offline and archival uses.
The Online version of this document is the most up-to-date and in the case of conflict the Online version prevails over any downloaded, saved or printed version.

This update of the Code Of Practice was issued 1 June 2026.

 

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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

1 Introduction 

The NZ Metal Roof and Wall Cladding Code of Practice (COP) is published by NZ Metal Roofing Manufacturers Inc. (MRM), to provide:

  • acceptable trade practice for fixing metal roofing, metal wall cladding, and accessories,
  • prescriptive detailing for designers, and
  • sets a benchmark for the standard of detailing and workmanship required over and above that required to comply with the NZBC.

The COP does not describe or dismiss alternative methods, which may need specific acceptance by the Building Consent Authorities.

It is published in accordance with current technology, materials, and building codes. The COP will be periodically updated to reflect changes in legislation and standards or improvements in technology and available materials.

The most current Code of Practice is available on the MRM website, www.metalroofing.org.nz/cop, as Code of Practice Online (MRM COP Version 26.03).

The latest changes to the NZMRM Metal Roof and Wall Cladding code of Practice were Published on 1 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

2 Glossary 

The glossary section provides definitions and descriptions of commonly used terms, as well as illustrations of domestic cladding terminology, industrial cladding terminology, and profile geometry.

 

 

3 Structure 

The information in this section explains the various factors used in calculating design loads and in resisting those loads to ensure roofs are structurally sound and meet the objectives of NZBC B1 Structure.

The designer must be familiar with the performance requirements of the New Zealand Building Code (NZBC). Loads can be calculated by following the relevant standard, while maximum span and fastening patterns can be specified following the manufacturer's literature.

For buildings designed to NZS3604:

  • G550 Steel Cladding Fastening Pattern Tables, and
  • Aluminium Fastening Pattern Tables

For SED projects to AS/NZS 1170, designers can use:

  • Steel Cladding Wind Load Span Graphs, and  
  • Aluminium Cladding Wind Load Span Graphs.  

It is the responsibility of the roofing contractor to install roof cladding according to the design and raise any concerns with the designer before commencement.

4 Durability 

Corrosion (B2-Durability) covers considerations for continued performance of roof and wall cladding over the building lifecycle.
Key topics include:

  • Material performance and coatings.
  • Corrosion: environmental categories and special climates.
  • Material compatibility — both "in contact with" and "runoff onto". See the 4.9.4A Interactive Material Compatibility Tool.
  • Maintenance for prevention and remediation of corrosion.

5 Roof Drainage  

This section considers the design of water drainage from the time it hits the roof cladding to the time it enters the downpipe. As the design considerations are similar, this also includes the discharge from gutters and troughs within the roof plane, valleys, internal gutters, and external spouting.

The Roof Drainage section gives guidance for compliance with NZBC Clause E1 Surface Water. It describes how to drain rainwater effectively from roofs and gutters.

 

The Code of Practice provides several interactive calculators:

5A Capacity Calculations

Gutter Capacity 5.4.7 Gutter Capacity Calculator
Valley Capacity (both symmetrical and asymmetrical) 5.5.7 Valley Capacity Calculator
Downpipe Capacity 5.7.3 Downpipe Capacity Calculator
Maximum Area Above Spreaders 5.8.1 Maximum Area Above Spreader Calculator
Maximum Area Above Penetrations 9.4.4 Maximum Area Above Penetration Calculator
Maximum Run 7.1.4 Maximum Run Calculator

6 External Moisture Overview 

The primary function of a roof is to shed external moisture. The Code of Practice deals with External Moisture in four sections, allowing for more detailed discussion. The solutions in the COP relate to all buildings and are not limited to buildings within the scope of NZS 3604.

Included in the COP under External Moisture:

6 External Moisture Overview provides an extract from NZBC E2 External Moisture. It highlights the Objectives, Functional Requirements, Performance Requirements, and Limits of the NZBC Clause E2. The second half highlights the scope and extent of Acceptable Solution E2/AS1.

7 External Moisture Roofing discusses the external moisture requirements and strategies for dealing with external moisture where it concerns metal roof and wall cladding.

8 External Moisture Flashings suggests strategies of managing external moisture with a specific focus on flashings.

9 External Moisture Penetrations focus specifically on managing external moisture and preventing leaks around penetrations.

7 External Moisture Roofing 

This section should be read in conjunction with 6 External Moisture Overview.

8 External Moisture Flashings 

This section should be read in conjunction with 6 External Moisture Overview and  9 External Moisture Penetrations.

The purpose of a flashing is to divert water away from any point of entry and to make a building weatherproof.

Flashings are not only required to weather the many junctions on a roof or wall structure but are often a highly visible part of the roof and wall cladding design. Therefore, they perform an important role in the aesthetic appearance of the building.

It takes longer to make and install flashings than fixing roof or wall cladding, so designers should be aware of the cost effects of design complexity.

See it in action with Roofguide

Many common flashing solutions are expanded on with step-by-step, interactive 3D instructions in the RANZ Roofing Guide, developed by the Roofing Association of New Zealand in association with the NZMRM.

Works on desktops, laptops, tablets and phones.

Subscribe Now - Professional More information Subscription for NZMRM/RANZ members

8A

roofguide_flashing.png

Roofguide Flashing Example
Subscribe Now - Professional More information Subscription for NZMRM/RANZ members

9 External Moisture Penetrations 

This section should be read in conjunction with 6 External Moisture Overview and 8 External Moisture Flashings.

A penetration is any hole cut in a roof or wall cladding to accommodate projections such as pipes, ducts, chimneys, roof lights doors and windows.

This section focusses on roof penetrations only. The type of penetration design is determined by:

  • the size of the hole,
  • shape,
  • the roof pitch,
  • the type of roof,
  • the catchment area,
  • placement on the roof, and
  • aesthetic requirements.

Designers are urged to consider what type of penetration design matches the building application and their customer’s needs, and detail accordingly, rather than allow the installer to make an on-site decision.

 

See it in action with Roofguide

Many of the penetration details in the Code of Practice are expanded on with step-by-step, interactive 3D instructions in the RANZ Roofing Guide, developed by the Roofing Association of New Zealand in association with the NZMRM.

Works on desktops, laptops, tablets and phones.

Subscribe Now - Professional More information Subscription for NZMRM/RANZ members

9A

roofguide_pen.png

Roofguide Penetration Example
Subscribe Now - Professional More information Subscription for NZMRM/RANZ members

10 Internal Moisture 

The science of internal moisture control is concerned with the need to manage and control condensation, mould growth, and corrosion.  
The outdoor environment, the building design, and occupant behaviour affect humidity in the living spaces, which ultimately affects humidity in the ceiling space.  
This section of the COP focusses predominantly on managing humidity in the ceiling space of dwellings. Shorter sections also cover the design of non-residential roof and wall cladding, which may also be affected by excessive internal moisture. 

 

11 Natural Light 

Natural Light covers the use of translucent roofing material for providing interior illumination. These typically take the form of profiled sheeting, stand-alone units, or flat sheet systems.

Skylights profiled to match the roof sheeting may be made from glass-reinforced polyester or polycarbonate. Proprietary stand-alone skylights may have polycarbonate, glass, or acrylic panels. Single or multi-skinned sheet products can be used in conjunction with proprietary support systems to replace glass in conservatory-type situations.

Main headings include:

  • Compliance
  • Profiled roof lighting
  • Stand-alone roof lighting
  • Sheet systems

12 Fitness For Purpose 

In addition to Corrosion (NZBC: B2 – Durability), other issues which may affect the lifespan or perceived quality of metal roof and wall cladding, include:

  • Oil Canning.
  • Purlin Creasing.
  • Colour Differential.

13 Safety 

This section highlights some aspects of the New Health and Safety at Work Act 2015 (HSWA 2015), including:

  • responsibility,
  • working at height in New Zealand, and
  • working on roofs.

HSWA 2015: Objective

The objective of The Health and Safety at Work Act 2015 is protecting the health, safety, and wellbeing of workers, and other people.

Information used in this section was retrieved from http://www.legislation.govt.nz/act/public/2015/0070/55.0/DLM5976660.html and worksafe.org.nz.

14 Installation 

Metal roof and wall cladding should be installed as described in this section to comply with the NZBC and to qualify manufacturers' warranties.

 

15 Other Products 

Other roofing products include:

  • Curved Roofs.
  • Solar Units.
  • Pressed Metal Tiles.
  • Standing Seam Cladding.

 

16 Maintenance  

Maintenance is defined as 'to keep in good condition or repair', and can be divided into four categories:

  • Reactive
  • Scheduled
  • Preventative, and
  • Special

17 Testing and MRM Standards 

The NZMRM employs specific testing methods and standards to evaluate the performance of metal roofing components and accessories.

Structural testing of profiled metal closely follows the standards AS 1562 and AS 4040, but differs in minor areas to suit NZ requirements.  This testing is used to demonstrate compliance with NZBC B1 – Structure

Compliance with NZBC B2 – Durability is demonstrated by testing of profiled metal and fasteners.  This testing is based on AS/NZS2728 and AS/NZS 3566 respectively, again with some modifications.

Also included, are the MRM soft edge standard, and testing and performance standard for pre-painted coil.

18 Useful Tools 

Useful tools and tables to do calculations and conversions for roof and wall cladding. Just choose the correct online calculator, input your values, and get the answer.

19 Revision History 

Policy for Updates to NZ Metal Roof and Wall Cladding Code Practice.

All revisions to clauses of the COP after June 2018 are recorded at 19 Revision History, including a brief explanation of the change.

See sub-clauses for detail of revisions at particular dates.

  • Reproductions of specific sections from the Code of Practice at a particular date are available on request by emailing admin@metalroofing.org.nz.
  • From June 2026, the PDF Download of the Code of Practice contains detailed revision history for only changes made to the current edition. 
    A PDF version of the full revision history to June 2018 is available at metalroofing.org.nz/RoofingCOP_RevisionHistory.pdf.
    The online Code of Practice retains the full revision history.

Revisions are split into 3 categories for simple assessment by users:

19A Revision Categories

Category

Description

Notification

Category 1 - Minor Errata

Correction to spelling, grammar or formatting that have no bearing on on the substance of the clause.

Recorded on website only - not individually included in emailed update

Category 2 - Editing and rearrangement

A clause or section of clauses has been rewritten to some extent for better articulation of the existing recommendation.

Existing citations of the COP in project documentation may be less clear as a result, but recommendations are not altered.

Recorded on website, and will be cited in emailed update as either specific or summary information as appropriate.

Category 3 - Substantial change to recommendation

A substantial change in a specific recommendation of the COP has taken place.

A review of existing project documentation against the new clause is considered essential.

Recorded on website, and explained with detail in emailed update