Access the Code of Practice online

This registration will be required once-only per browser/device, which is achieved using a cookie stored on your device.

There is no password required, and your information will not be shared with any third parties.

Please register and accept the terms for the NZMRM online COP
By ticking this box you confirm that you have read and accept the Terms listed below


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 v24.03:Durability; Environmental-Categories

4.6 Environmental Categories 

Suppliers of pre-painted metal offer alternative products for different environments, using different metallic coatings, paint systems, paint thickness and metals. The designer or the roof cladding contractor should carefully assess and evaluate these options to comply with the NZBC.

The boundaries of different corrosion zones are difficult to define because many factors determine the corrosivity of a particular location. The designer should choose the appropriate materials for the location, which meet the minimum durability requirements of the NZBC and satisfy customer expectations.

4.6.1 Assessment of Marine Environments 

Wind is responsible for the salinity present in marine atmospheres. The wind picks up particles of salt from breaking waves and can carry them inland. The quantity of salt aerosol entrained by the wind is affected by many factors, such as wind strength, wave height, the width of the generation zone, and the contours of the seabed and coastline. These factors along with the persistence of the wind from a given quarter determine the corrosivity of a shoreline.

While salt deposits are measurably present in inland areas such as Taupo, the main effect of marine atmospheres reaches just a few hundred metres from the shore.  Particles of salt in the air deposit on adjacent surfaces through gravity and contact; the rate at which deposits settle is affected by the roughness of the ground that the salt-laden air passes over. Obstacles such as trees slow the wind down, increasing the rate of gravitational deposit, and bringing the salt aerosol in more contact with surfaces on which they can deposit.

On the other hand, open flat land and natural “wind tunnels” can allow quite high concentrations of salt to travel several hundred metres inland.

A site’s location, relative to the sea or marine inlets, is a common method used to assess the corrosivity of a location. The distance from salt water for a given Zone varies with the location, depending on the prevailing winds and roughness of water in those areas, as well as the evenness of the terrain it passes over.

Where environmental Zones overlap, a site-specific evaluation may help define the category into which it best fits.  Visual evidence of corrosion on adjacent metal surfaces may be present, ground roughness can be assessed, industrial influences can be evaluated and data about the persistence of onshore winds can be obtained from NIWA.

More local factors that affect the corrosivity of a specific location include:

  • Overhanging shade increases the time of wetness of a structure and corrosion rate.
  • High levels of water roughness such as caused by strong tidal flow against the wind direction, as is often experienced in areas such as Cook Strait, increases salt spray.
  • Surfaces not receiving regular and effective rain washing or sufficient manual washing may experience corrosion rates two to three times that of cleaned surfaces.

There are many ways of more accurately determining the actual corrosivity of a given location. The most commonly accepted method as outlined in ISO 9223 is measuring first-year corrosion rate of different metals: mild steel (MS), zinc, aluminium and copper. The COP uses the first-year corrosion rate of mild steel as the most relevant and reliable indicator of a location’s corrosivity.

The names given by different Standards for given corrosion zones vary. The Corrosion Zones in the Code of Practice are similar to those published in NZS 3604:2011 except that:

  • the COP makes a distinction between Harbours, West Coast, and East Coast shorelines, and
  • NZS 3604 Zone D (High) is further broken down into E (Very High) and F (Extreme Marine) because, in NZS 3604 Zone D, the first-year mild steel corrosion rate can vary from 200 g/m2 to 1000 g/m2.

 

4.6.1A Corrosion Zone Categorisation and First year Mild Steel Corrosion Rate (g/m²)

NZS3604Code of PracticeDescriptionMS Corrosion Rate (g/m²)
BA  (Mild)Far inland, with no industrial pollution or thermal activity, or dry internal. This condition is not commonly found externally in New Zealand.1 – 10
B  (Moderate Inland)Most dry rural areas in New Zealand, 50 km from the coast, are in this category. It can extend closer to the coastline of sheltered water in low rainfall areas.10 – 80
CC  (Moderate Marine)This category covers area of low marine influence. It can extend from 50 km inland to within 1 – 1.5 km of west coast beaches, or be in the immediate vicinity of calm estuaries.80 – 200
DD  (Severe Marine)In this category, marine influences are frequently apparent. Its proximity to the coast is determined by the roughness of the water, prevailing winds, ground roughness and sheltering.200 – 400
E  (Very Severe Marine)In this category, the structure is normally exposed and marine influences are almost constantly apparent.400 – 650
F  (Extreme Marine)This category is rare in a building site. It would be an exposed location very close to breaking surf.650 – 1 000

4.6.3 Material Selection 

Note: this is the minimal requirement to achieve compliance with NZBC Clause B2-Durabilty.  Meeting the minimum requirements of NZBC clause B2 Durability does not necessarily represent optimal product selection. In a transition zone, it may be more cost effective over the life cycle of the building, and for meeting customer expectations, to choose a more durable option.

4.6.3A Material Selection : Exposed Roofs and flashing

Durability Required : 15 years

Marine ZoneExposed Fastener
Class (minimum)
Acceptable Materials
***As defined by AS/NZS 2728.
B:
Moderate Inland
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
  • AZ 150 coated steel
  • Galvanised steel Z 450
C:
Moderate Marine
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
  • AZ 150 coated steel
  • Galvanised steel Z 450
D:
Severe Marine
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
E:
Very Severe Marine
C5
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
F:
Extreme Marine
C6
  • Aluminium
  • Pre-painted aluminium
 
Materials accepted by NZMRM as complying with coating types include:
  • Painted steel Type 4:
    Colorsteel® Endura®, Colorcote® ZinaCore™
  • Painted steel Type 6:
    Colorsteel® Maxx®, Colorcote® MagnaFlow™, Colorcote® MagnaFlow X™

 

4.6.3B Material Selection : Walls*, fascias and sheltered roofs and flashings

Durability Required : 15 years

Marine ZoneExposed Fastener
Class (minimum)
Acceptable Materials
*The practicality of carrying out regular maintenance, and difficulty of replacement, should also be considered when considering wall cladding material options.
***As defined by AS/NZS 2728.
B:
Moderate Inland
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
  • AZ 150 coated steel
  • Galvanised steel Z 450
C:
Moderate Marine
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
  • AZ 150 coated steel
D:
Severe Marine
C4
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
E:
Very Severe Marine
C5
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
F:
Extreme Marine
C6
  • Aluminium
  • Pre-painted aluminium
 
Materials accepted by NZMRM as complying with coating types include:
  • Painted steel Type 4:
    Colorsteel® Endura®, Colorcote® ZinaCore™
  • Painted steel Type 6:
    Colorsteel® Maxx®, Colorcote® MagnaFlow™, Colorcote® MagnaFlow X™

 

4.6.3C Material Selection : Flashings Behind Cladding

Durability Required : 50 years

Marine ZoneAcceptable Materials
**Stainless steel must not be in wet contact with metallic coated steel, plain or painted.
***As defined by AS/NZS 2728.
B:
Moderate Inland
  • Stainless Steel**
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
  • Pre-painted steel Type 4***
  • AZ 150 coated steel
  • Galvanised steel Z 450
C:
Moderate Marine
  • Stainless steel**
  • Aluminium
  • Pre-painted aluminium
  • Pre-painted steel Type 6***
D:
Severe Marine
  • Stainless steel**
  • Aluminium
  • Pre-painted aluminium
E:
Very Severe Marine
  • Stainless steel**
  • Aluminium
  • Pre-painted aluminium
F:
Extreme Marine
  • Stainless steel**
  • Aluminium
  • Pre-painted aluminium
 
Materials accepted by NZMRM as complying with coating types include:
  • Painted steel Type 4:
    Colorsteel® Endura®, Colorcote® ZinaCore™
  • Painted steel Type 6:
    Colorsteel® Maxx®, Colorcote® MagnaFlow™, Colorcote® MagnaFlow X™