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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:Installation; Fasteners

14.13 Fasteners 

The durability of fasteners should equal or exceed that of the material being fastened, and the fastener metal or coating must be compatible with the cladding material if in contact. Fasteners used pre-painted steel products should be factory colour matched before installation.

14.13.1 Nails 

The traditional New Zealand roof fastener was until 1980 the "Lead Head", a flat-headed smooth shank steel nail with a lead head cast on it. Lead heads often 'backed out' causing leaks, the shanks were prone to corrosion, and lead is incompatible with modern metallic coatings.
Spiral Shank nail fasteners have a galvanised shank, and the spiral shank has over twice the withdrawal resistance of a smooth shanked nail. They are however still prone to backing out, and the under-head seal is not as robust as the neoprene seals used on modern roofing screws.

The COP recommends using screws rather than driven fasteners, in all cases.

 

14.13.1A Nail Pull-out

Driven Fasteners can back out over time.

 

14.13.2 Screws 

Screw fasteners should be long enough to give adequate penetration into the supporting structure. Generally, 30 mm embedment is required for screws into timber or three threads engagement for screws into steel. Refer to roofing manufacturers for specific recommendations.

Fasteners should be:

  • a minimum of Class 4 for Severe Environments,
  • Class 5 for Very Severe Environments,
  • manufactured and coated with materials compatible with the material being fastened, and
  • fitted with low-carbon, non-conducting sealing washers.

Profiled washers should have an EPDM sealing washer.

 

14.13.2C Screw Gauge and Thread

GaugeNominal Shank Diameter
mm
62.5
83
103.5
124.1
144.8
 

Screw fasteners are identified by their length, gauge pitch (threads per inch) and their drill point. The drill point may be type 17 for driving into timber or drill point for driving into steel. Reduced diameter drill points, which can be used for either function, are also available.

14.13.3 Clip Fasteners 

Secret-fixed roofs will be attached to the primary structure by a proprietary clip that is screwed or nailed to the purlins. These profiles offer the advantages of fewer penetrations through the cladding, and thermal expansion is unimpeded.

Clip and bracket fasteners can be purpose made to provide the same attributes to most flashings.

14.13.4 Rivets 

Rivets should have a minimum diameter of 4 mm.

Use aluminium rivets for galvanised sheets and aluminium/zinc-coated steel products; monel rivets are incompatible with aluminium and zinc products.

Sealed rivets are preferred over unsealed rivets, as they do not require adding sealant on the face to achieve weatherproofing.

 

14.13.4A Rivet Setting

Blind rivets are placed through a pre-drilled hole then are set by rivet tool withdrawing the mandrel. This expands the rivet pin, clamping the material between the rivet pin and the rivet head. The pin eventually snaps free.