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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 v24.12:External-Moisture;

External Moisture Overview 

The primary function of a roof is to shed external moisture. The Code of Practice deals with External Moisture in four sections, allowing for more detailed discussion. The solutions in the COP relate to all buildings and are not limited to buildings within the scope of NZS 3604.

Included in the COP under External Moisture:

6 External Moisture Overview provides an extract from NZBC E2 External Moisture. It highlights the Objectives, Functional Requirements, Performance Requirements, and Limits of the NZBC Clause E2. The second half highlights the scope and extent of Acceptable Solution E2/AS1.

7 External Moisture Roofing discusses the external moisture requirements and strategies for dealing with external moisture where it concerns metal roof and wall cladding.

8 External Moisture Flashings discusses strategies of managing external moisture with a specific focus on flashings.

9 External Moisture Penetrations focusses specifically on managing external moisture and preventing leaks around penetrations.

6.1 NZBC Clause E2 External Moisture (Extract) 

6.1.1 E2 Objective 

The objective of this provision is to safeguard people from illness or injury which could result from external moisture entering the building.

6.1.2 E2 Functional Requirement 

Buildings should be constructed to provide adequate resistance to penetration by, and the accumulation of, moisture from the outside.

6.1.3 E2 Performance Requirements 

  1. Roofs shall shed precipitated moisture and snow.
  2. Roofs and external walls shall prevent the penetration of water that will cause dampness or damage to the building elements.

Other performance requirements quoted relate to transmission of ground moisture, areas below suspended floors, condensation in concealed cavities, and construction moisture.

6.2 Compliance 

In the context of COP Roof drainage, NZBC E1 requires that water discharging into a gutter must have less than a 2% probability of entering a building.  This means that those drainage paths inside the building envelope, including valleys and internal gutters, must be designed to accommodate a 50-year rainfall intensity over a short period.  Roof Drainage Design discusses how the COP addresses this in more detail.

The above caveat equally applies to the limitations on run length of roof cladding, drainage capacity around penetrations, and discharge of spreaders, which are dealt with in:

Gutter catchments outside the envelope, which can discharge freely without entering the building, can be calculated using less rigorous safety factors

6.3 Related Topics 

NZBC E2 – External Moisture is primarily focussed on a buildings’ external envelope being able to resist weather infiltration.

Acceptable Solution E2/AS1 also has some information on gutter sizing and durability, but these are also covered in E1 – Surface Water and B2 – Durability.

E2/AS1 also has some prescriptive solutions for structure regarding roofing spans which are omitted from B1 - Structure.

For clarity, this Code of Practice deals with the following topics discretely: