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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 v24.03:Durability; Clearances

4.15 Clearances 

To ensure the edge of the flashing does not mechanically remove protective coatings on the cladding, there must be enough clearance between the edge of a vertical flashing, or a notched flashing, and the cladding. Similarly, the edges of cladding running parallel to flashings, such as at a window head, should have clearance to avoid mechanical damage and allow drainage.

Having the lower edges of flashings apart from the surface they are covering helps to improve the cut edge durability of the flashing. Kick-out barge details are preferred to bird’s beak barge details for the same reason. The size of the clearance is not critical, but typically it is more than 5 mm.



4.15.1 Ground Clearance 

Clearance is required between the bottom of profiled metal cladding and large flat surfaces. For timber-framed dwellings, E2/AS1 requires a clearance of 35 mm to an adjacent roof, 100 mm to paved ground, and 175 mm to unpaved ground.

The clearance requirements for unlined buildings are less than that required for lined buildings, as the absence of lining enables the inner face of the cladding to dry more rapidly, and inspection and maintenance of the framing can be practically achieved.

4.15.1B Importance Levels from NZS 3604:2011 (Table 1.1)

Level 1Structures presenting a low degree of hazard to life and other property
Level 2Normal structures and structures not in other importance levels
Level 3Structures that may contain people in crowds or contents of high value to the community, or may prose risks to people in crowds.
Level 4Structures with special post-disaster functions.

4.15.1C Minimum Ground Clearance for Lined Buildings

Minimum Design Ground Clearance for
Profiled Metal Cladding on Lined Buildings of Importance Level 2.
Ground TypeMinimum Clearance
Garage door opening25 mm
Walls under canopies35 mm
Paved100 mm
Unpaved gravel125 mm
Unpaved lawn150 mm
Unpaved pasture175 mm


Importance level 1 buildings may have a lesser clearance provided occupant maintenance prevents the build-up of debris against the cladding.

Greater clearance may be required where gardens abut a wall, where lawn grasses are not grazed or maintained, or where soil spillage from adjacent banks may occur. Future landscaping effects on ground levels must also be considered.

4.15.2 Site Management 

The effectiveness of clearances in achieving durability requirements is subject to the occupant ensuring that vegetation, debris, and soil do not build up against the cladding surface. Design clearance from a surface is no guarantee of durability as effective clearances are subject to site development, occupant behaviour and building maintenance.

4.15.2A Cladding Open to Air

Cladding which is open to air will experience the normal wet/dry cycles for which it is designed.

4.15.2B Vegetation in Contact with Cladding

Vegetation or earth in contact with the cladding will increase the time of wetness and may contain corrosive compounds.

The separation of profiled metal claddings from corrosive surfaces such as wet timber or concrete is more critical at the bottom end of cladding, where high humidity levels may be experienced for extended periods. This may take the form of a 3 to 6 mm gap, an inert self-adhesive tape or a PVC vermin strip.

Internal environments are also important, ventilation must be adequate for the building use, and absorptive of corrosive substances must not be in prolonged contact with the external or internal face of the cladding or structure.

4.15.2C The Result of Debris Build-up Against Cladding

Allowing build-up of material against wall cladding can result in corrosion regardless of nominal ground clearance.