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 Downpipe Capacity Calculator and 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 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 Asymmetrical Valley designs.
- The clause Metal Wall Cladding Flashings 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 Area Above Spreader Calculator now features an additional callout to draw attention to Condition 3.
- We revised the Roof Cladding Expansion Provisions required for controlling expansion in aluminium.
- We added a recommendation for fastener identification to be stamped on fastener heads to MRM Fastener Performance Requirements and Testing.
- The illustration for Ventilation Pathway: Top Plate with Underlay was updated to show how a baffle can be used to improve ventilation.
- The PDF Download of the Code of Practice now contains detailed revision history for only changes made to the current edition. The online Code of Practice retains the full detail at Revision History, and a PDF version of the full revision history is available at metalroofing.org.nz/RoofingCOP_RevisionHistory.pdf.
- Log in to post comments