COP v3.0: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 the fixing of metal roof and 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,, as Code of Practice Online (MRM COP Version 3).

The most recent updates to the NZ Metal Roof and Wall Cladding Code of Practice were published on 1 June 2023.

Substantial change to recommendations:

The main section 3 Structure has been comprehensively revised.

Other important updates:

  • A new clause discusses 12.3 Flashing Buckling in more detail, while the old clause has been renamed Compression Timber.
  • Standing Seam Cladding has been renamed 15.4 Tray Roofing and the entire clause and its sub-clauses have been reviewed.
  • The definition of standing seam roofing (a form of tray roofing installed on solid sarking using traditional seaming tools) has been clarified.

The rest of the updates consisted of minor corrections and edits.

For more detailed information, see 19.1 2023 – June.

1.1 Disclaimer and Copyright 

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.

This is the current online Code of Practice, published in December 2017.

  • Sections marked as Version 3.0 contains new, substantially updated information and interactive tools.
  • Sections marked as V2.3 denotes a revised edition of V2.2 (published in November 2012)

New Zealand Metal Roofing Manufacturers Inc. (NZMRM) periodically updates the information contained in this Code.

Before using this Code, please refer to the New Zealand Metal Roofing Manufacturers Inc. website ( for the most recent updates on information contained in this Code.

1.2 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.

1.3 Standards and Related Documents 


NZ 22952017Pliable, permeable building underlays. (either NZS 2295 2017 or NZS 2295 Amendment 1 2017)
NZS 36022003Timber and wood based products for use in building.
NZS 36031993Amendment 4 2005 Timber Structures Standard.
NZS 36042011Timber Framed Buildings.
AS/NZS 1170.02002Amendment 5 2011 Structural design actions. General Principles. Commentary to Parts 0, 1 and 2.
AS/NZS 1170.12002Amendment 2 2009 Structural design actions. Permanent, imposed and other actions.
AS/NZS 1170.22011Amendment 4 2016. Structural design actions. Wind Actions.
AS/NZS 1170.32013Amendment 1 2007 Structural design actions. Snow and ice actions
AS 1562.11992Design and Installation of sheet roof and wall cladding – Part 1 Metal
AS 1562.32006Design and Installation of sheet roof and wall cladding – Part 3 Plastic (was AS/NZS 1562.3 1996)
AS/NZS 17341997Aluminium and aluminium alloys - Flat sheet, coiled sheet and plate
AS/NZS 27282013Prefinished/prepainted sheet metal products for interior/exterior building applications—Performance requirements
AS/NZS 42571994/97Plastic roof and wall cladding materials. Parts 0-9 Methods of Test.
AS/NZS 43892015Roof Safety Mesh.
AS/NZS 46002005Amendment 1 2010. Cold-formed Steel Structures.
AS 13912007(R2017) Metallic materials - Tensile testing at ambient temperature
AS 13972012Continuous hot-dip metallic coated steel sheet and strip - Coatings of zinc and zinc alloyed with aluminium and magnesium
AS 3566.120021. General requirements and mechanical properties
AS 3566.220022. Corrosion resistance requirements. (Withdrawn)
AS 42562006Plastic roof and wall cladding materials. (Now AS only previously AS/NZS 4256 1994). Parts 1-5. Plastic materials.
BS 14701987Specification for wrought aluminium and aluminium alloys for general engineering purposes. (Replaced by 9 EN Standards) See AS 1734
BS 28701980Specification for rolled copper and copper alloys. (Replaced by EN standards)
BS EN 9881987and BS EN 1179 2003 Specification for zinc alloy sheet and strip
ISO 92232012Corrosion of metals and alloys. Corrosivity of atmospheres - Classification.
ISO 92242012Corrosion of metals and alloys. Corrosivity of atmospheres - Guiding values for the corrosion categories.
ISO 92252012Corrosion of metals and alloys -- Corrosivity of atmospheres -- Measurement of environmental parameters affecting corosivity of sites
ISO 92262012Corrosion of metals and alloys -- Corrosivity of atmospheres -- Determination of corrosion rate of standard specimens
AS/NZS 3500.32015Stormwater drainage
AS/NZS 2179.12014Metal shape or sheet rainwater goods, and metal accessories and fasteners
AS 21801986Metal rainwater goods - Selection and installation
HB 1141998Guidelines for design of eaves and box gutters
AS 43122008Atmospheric corrosivity zones in Australia
HB 392015Installation code for metal roofing and wall cladding
AS/NZS 23122002Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings
AS 4040.01998Methods of testing sheet roof and wall cladding Introduction, list of methods and general requirements
AS 4040.11998Methods of testing sheet roof and wall cladding Resistance to concentrated loads
AS 4040.21998Methods of testing sheet roof and wall cladding Resistance to wind pressures for non-cyclone regions
AS/NZS 4200.12017Pliable building membranes Part 1: Materials
AS 4200.22017Pliable building membranes Part 2: Installation

1.4 Acknowledgements 

The MRM Technical Committee continuously update this COP, which was originally authored by Stuart Thomson.

Our thanks to advisors, designers and trades people for their input.

1.5 Disputes 

Under the provisions of the Building Act and the NZBC, a contractor who undertakes to do work on a building implies that he can produce an effective and sound result which will fulfil its intended purpose.

There is a customer expectation, backed by consumer legislation, that the finished work will leave the building weathertight, and the work done will comply with the NZBC and will be to a standard that is described as “acceptable trade practice”.

“Acceptable trade practice” and “good trade practice” for the Roofing Industry are both described and contained in this Code of Practice. In addition to any contractual or verbal offer there may also be a written obligation given in the form of a warranty. See 16.9 Material Selection

All contractors should ensure that materials they use comply with the requirements and specifications contained within this Code of Practice. All suppliers’ or manufacturers’ product literature should be dated; and where superseding previous literature the dates should be referenced. The user must ensure that suppliers or manufacturers product literature is the latest version published.

Contractors must be satisfied that the product as described in the product literature is acceptable to the Territorial Authority, and contractors must be aware of their liability under law and the contractual documents they have signed or agreed to.

Customer expectation is supported by law that states that the material and product used must be fit for its intended purpose, and the liability of each of the parties is assessed on their ‘failure to warn that the product would not fulfil a perceived function".

Poor workmanship is a common cause of dispute and it is often given as the reason for non-payment between the sub-contractor and contractor or owner. This Code of Practice provides a standard of workmanship and a benchmark for arbitration.

It is in the interest of all parties to avoid the cost and delay of litigation and although there are other voluntary ways to settle disputes, they all require some compromise by those concerned.

One voluntary method is negotiation by calling a site meeting where all interested parties can air their grievances across a table and draw up a programme of rectification and reach an agreement over responsibilities and payment.

Any agreement must be recorded, signed and state what is to be done, how much is to be paid, by whom, by when, and how it will be accepted and checked. If no agreement can be reached then a solution may be found through mediation.

The Weathertight Homes Resolution Services Act 2006 provides for a mediation service to be available to dwelling/house owners with eligible claims. The claiming owner and any of the other parties against whom the claim is made may agree to refer the claim to mediation, with provision for binding settlements by agreement. This service is restricted to leaky homes built within 10 years of the claim.

1.5.1 Mediation 

Mediation is a cost-effective, confidential, and voluntary process where the mediator is the facilitator who assists the parties to come to a negotiated agreement. Mediation concentrates on the parties’ interests rather than on their rights, when often both parties realise that they are partly at fault and wish to resolve the dispute and accept a compromise, as opposed to litigation. Any recorded settlement in a mediation agreement can be enforced as a contract, but if they cannot reach a settlement, they can refer to arbitration or the courts.

A mediator acceptable to all parties is appointed and should act independently, avoid unnecessary expense and comply with the principles of natural justice. The mediator's task is to help the parties identify the issues and options for settlement and look for a settlement that is equitable to all concerned. All relevant documents including specifications, plans, quotations, and written submissions setting out the basis of the complaint and the rebuttal by the other party must be made available to the mediator.

After an investigation, site visits, and discussion with all the parties, the mediator, using trade benchmarks such as this Code of Practice and drawing on experience can apportion responsibilities and instruct rectification work be done. This method can provide a quick and inexpensive outcome with costs shared by both parties, but the decision is not binding and must be mutually agreed to.

Informal resolution of disputes does not necessarily uncover the facts; and as material or installation failures are not necessarily publicly disclosed, improvement can be inhibited.

Mediation does provide the opportunity to ‘move on’ and does not always jeopardize business relationships as litigation invariably does.

1.5.2 Adjudication 

The Construction Contracts Act provides for a process of dispute resolution called adjudication, to be the first option if negotiation fails. It provides a thirty-day formal process whereby the adjudicator is appointed by the claimant, and the respondent cannot opt out. The process is designed mainly for payment disputes, but it can also be used for workmanship disputes and is expected to become the normal dispute resolution method in the Construction Industry.

The adjudicator's decision, called a determination, is binding and enforceable by the courts. An unsatisfied party can only appeal an adjudication after complying with the determination. The adjudication is subject to confidentiality, except by mutual consent or if the information is already in the public domain.

The disadvantage of both mediation and adjudication is that the faults are not made known to the roofing industry, who should be able to learn from the mistakes of the past.

Where the amount in question is under $7,500, or $12,000 by agreement with the other party, an alternative method is to file the complaint with the Disputes Tribunal. The parties usually represent themselves, without lawyers, and a compromise outcome is sought by a referee. This method of settlement gives no assurance of an equitable outcome or that the outcome will be based on technical grounds; the main purpose of this court is to seek agreement between the parties.

1.5.3 Arbitration and Litigation 

Arbitration is usually a strict and formal process similar to litigation in which the parties may be legally represented and select and pay for the arbitrator. Arbitrators must comply with the Arbitration Act; their imposed decision is known as an award, and it is final and binding.

The final and expensive alternative is litigation. That usually involves suing for breach of contract, non-payment, non- performance, faulty materials, or non-compliance. Judgment is publicly imposed and usually made by comparison with “state of the art” materials and practice available at the time the contract was signed.

Both arbitration and litigation can be prolonged and the parties’ cost may exceed the amount in dispute.

When roofing contractors sublet the contract, they assume the same responsibility as though they carried out the work.

To avoid disputes, roofing suppliers and contractors must give adequate instruction, training, and supervision. They should also keep their staff informed of industry developments and with the contents of the New Zealand Metal Roof and Wall Cladding Code of Practice.