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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:Testing-And-Mrm-Standards; Mrm-Fastener-Performance-Requirements-And-Testing

17.2 MRM Fastener Performance Requirements and Testing 

Durability testing of construction fasteners for external cladding, suitable for Moderate, Severe, Very Severe, and Extreme Environments.

Typical applications include the fixing of non-ferrous metals, metallic coated steel, and painted steel cladding products to a primary structure. The fasteners may be non-ferrous metal or metallic coated steel.

17.2.1 Requirements for Fastener Testing 

  1. Fastener systems, including washer, must not deteriorate to the extent that their intended function is impaired, for a minimum of 15 years or the life of the cladding.
  2. Fastener systems must not detrimentally affect the material being fastened for a minimum of 15 years or the life of the cladding.
  3. Colour adhesion and colour fastness are required to be similar to that of the cladding for a minimum of 10 years.
  4. Some shank corrosion is acceptable on screws with shanks exposed to the weather after 10 years.


The head mark on the self-drilling screw shall clearly show the manufacturer’s unique head mark and identify the corrosion resistance classification.

17.2.2 Test Panel Requirements 

The following is required: An outdoor exposure test site with known first-year mild steel corrosion rate assessed in accordance with ISO 9226. Test Location 

The outdoor corrosion test site shall be located in a cleared, well-drained area not subjected to shadowing from trees, buildings or structures. The site should not be subjected to direct splash from any water body or industrial pollution sources. If industrial or geothermal influences are present, the level at the site should be <90 μg/m3. Site Orientation 

The zinc corrosion rate at the outdoor corrosion test site shall be determined in accordance with ASTM G92 and ISO 9226, using mild steel coupons orientated 45° from the horizontal, facing directly into the prevailing winds and surf.

The test panels must face the same direction as the steel coupons. Preparation of Test Panel 

A total of 100 screws shall be used for each of the test panel and for the control panel, of which 80 shall be crest fixed and 20 shall be valley-fixed in the configuration shown in Fastener Test Rack. The screws may be of a different style, but all screws shall have identical coatings and sealing washers. Screws shall be power-driven into the test panel at their recommended driving speeds and hole shall not be predrilled.

The cladding used in the test panel shall be standard corrugated profile manufactured from metallic coated steel, pre-painted steel, or non-ferrous metal in accordance with the cladding types the fastener is designed for.

Control panels may be used to assess the compatibility of screws and any accessories with their other building materials or test fastener performance against known benchmarks.



17.2.3 Fastener Performance Testing 

All cladding fasteners must be compatible with the material, suitable for the environment and have a durability equivalent to that of the cladding material. All exposed fasteners must have a minimum durability of Class 4. Site Testing 

Representative samples shall be exposed in a test site in the manner described in 17.2.2 Test Panel Requirements until 5% of samples show red rust on significant surfaces. The corrosion rating of the site (measured in first-year mild steel corrosion rate) and the time to failure will establish the screw class in accordance with the following graph.

Complete fastener assemblies, including washers and profiled washers, as appropriate, shall be tested as a system.

It cannot be assumed that colour match painted screws will perform a well as unpainted. Both painted and unpainted samples are required to be tested concurrently.



 Field Performance Validation 

The historical performance of fasteners exposed in a given environment over a number of years can be taken as a reliable measure of performance, but confirmatory testing in an approved, monitored location must also be done for validation. Accelerated Testing 

The MRM does not acknowledge accelerated testing as proof of performance. However, manufacturers may use it to compare similar coating systems, or for monitoring production quality control. Fastener Shanks 

Self-drilling screws which have the shanks and heads produced from the same parent material and undergo the same process and coating do not require the coatings on the shanks to be monitored. Self-drilling screws that have different head and shank material or processing shall require the corrosion resistance of the shank to be monitored as for the head. Sealing Washer Conductivity 

The maximum current flow through a sealing washer shall be equal to or below 0.5 × 10-6  A for all thermoset and thermoplastic materials, and shall be tested by the specified procedure in Appendix L. of AS/NZS 3566. Any current flow above this level shall be deemed as not meeting the requirements of this Standard.


17.2.4 Appearance 

Ultra Violet Resistance

Fasteners must not fade at more than twice the rate of fade as the roofing material.

General Appearance

Paint coatings should evenly match that of the cladding in terms of colour, and be reasonably intact after installation with approved screw setting methods. The degree of paint loss during installation will be subject to the fasteners’ visual exposure, but should not exceed 10% of the exposed surface in any circumstance.


Some visual corrosion is acceptable after 10 years exposure, to the degree that it doesn’t affect the integrity of the fastener or the cladding material and appears over less than 10% of the fastener’s surface.

17.2.5 Weatherproofing 

17.2.5A Mechanical and Thermal Properties of Seals

Mechanical and thermal properties of thermoset and Thermoplastic seals — batch control tests on Finished sealing washer product

Test StandardTest descriptionThermoset sealsThermoplastic seals
ASTM D2240Durometer hardness (Shore A)Tolerance ±5Tolerance ±5
ASTM D412Tensile strength (min. MPa) Ultimate Elongation (%)6 Min. 1253 Min. 200
ASTM D257DC resistance of finished articles when tested at 1000 V2000 MΩ2000 MΩ
Specific gravityTolerance ±0.02Tolerance ±0.02
Every batch of seals shall be tested to meet these requirements.  The nominal specific gravity and hardness shall be established for each product, and then tolerances in the table shall apply.

 Sealing Properties

The seal for a self-drilling screw should prevent loss of vacuum for 30 seconds when using the test procedure in Appendix K of AS/NZS 3566.



17.2.6 Fastener Performance Test Report 

The following information shall be included in the report:

  1. The report number and date.
  2. Reference to this test method
  3. Exposure site classification and identification.
  4. The date the test sample was exposed.
  5. The date of failure (5% showing red rust) was observed.
  6. Exposure time
  7. Fastener durability designation
  8. Name of a third-party auditor who monitored the test.
  9. Fastener Manufacturer and Product designation
  10. Test panel description, e.g., cladding material, base plates