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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 v23.12:Internal-Moisture; Nzbc-Clause-E3-Internal-Moisture

10.1 NZBC Clause E3: Internal Moisture (Extract) 

Source: Acceptable Solutions and Verifications for New Zealand Building Clause E3 Internal moisture.​

10.1.1 E3 Objective 

Safeguard people against illness, injury, or loss of amenity that could result from the accumulation of internal moisture.

10.1.2 E3 Functional Requirements 

Buildings must be constructed in a way to avoid the likelihood of:

  • fungal growth on linings and other building elements, and
  • damage to building elements due to the presence of moisture.

10.1.3 E3 Performance Requirements 

NZBC Clause E3 requires building practices to ensure an adequate combination of thermal resistance, ventilation, and space temperature in all habitable spaces, bathrooms, laundries, and other spaces where moisture may be generated or accumulate.

10.1.4 Compliance 

New Zealand Building Code clauses E3 – Internal Moisture and G4 – Ventilation focus on air quality and accumulation of moisture in occupied spaces. The acceptable solutions for these clauses do not specifically require ventilation of attic spaces.

While problems with excessive internal moisture in attic spaces are relatively uncommon, they can be severe. A poorly designed ceiling cavity, even above a well-aired room, can give rise to internal moisture problems in the attic space, which can affect the air quality of the occupied space below and may cause health and durability issues.

The COP requires building techniques which encourage trickle ventilation of all spaces in buildings; and requires specific ventilation design for:

  • flat roofs,
  • sarked roofs,
  • skillion roofs,
  • barrel curved and prickle-ridged roofs, and
  • roofs with ceilings which allow easy passage of moisture vapour.

Long (over 12 m spans), shallow-pitched (less than 12°) roofs should also be designed to allow natural ventilation.

Generally, there is no need to make provision for moisture control in industrial and most commercial buildings due to them being either well-ventilated or climate-controlled. In buildings with valuable or delicate stock, the possibility of dripping condensation needs to be assessed.

Roofs in cold areas where numbers of people may come in wet at the end of the day, such as ski lodges and tramping huts, require specific design.

Buildings designed to accommodate large numbers of people (such as theatres, sports areas and educational buildings) and areas creating particularly high moisture levels (e.g. swimming pools) should have ventilation solutions designed by a specialist engineer.