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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:Flashings; Sealants

8.7 Sealants 

Sealants play an important part in cladding because AZ or paint coatings cannot be sealed using solder.

The purpose of sealants used in the joints between metal roof and wall cladding and flashings is to prevent the entry of rain or snow and to exclude dirt, debris, and moisture by capillary action. They may also have varying degrees of adhesive action.

Sealants are generally Neutral Cure silicone or Modified Silicone (MS) types. The latter is generally paintable. Proprietary self-adhesive tape sealants are also entering the market and give excellent performance in certain conditions. Acid cure sealant, designed to bond to inert surfaces such as glass, must not be used.

Designs using sealants to seal sheet components must always include a mechanical fastening such as a screw, rivet or a mechanical seam. 

Generally, the function of a sealant is carried out by that sealant being sandwiched in the joint. In most cases, the post application of sealant to the outside of a joint is both futile and unacceptable.

The sealant does not require significant total adhesive strength, but it should bond positively to both surfaces as a continuous layer. To ensure complete sealant cure, the width of sealant in a lap should not exceed 25 mm when compressed

8.7.1 Methods Of Sealing 

There are two main methods of sealing metal sheets — gun applied sealants and self-adhesive tapes.

Sealants should have a low resistance to compression so that metal sheets can be brought closely together by their fasteners and not held apart by the sealant.

8.7.2 Surface Preparation 

For adequate bonding, all surfaces must be clean, dry and free from contaminants, such as rolling oils, dirt or dust. 

8.7.3 Sealant Extrusion And Placement 

Sealant should be gun-applied in a continuous flow to provide a joint without gaps or voids. This will prevent the entry of both condensation from above and water drawn up by capillary action, either of which can cause metal corrosion.

After placing the sealant cartridge in the gun, the tapered nozzle should be cut with a sharp knife at an angle of 45 ° at a position which would provide a bead of sealant approximately 6 mm in diameter.

Sealed rivets are the preferred fastener. The stem holes of unsealed blind rivets must be sealed with silicone, which can attract dust and look unsightly.

Sealant should be placed in a continuous bead close to the weather end, covering any pre-drilled rivet holes. If a complete ring of sealant is applied around the fastener, an air pocket forms which compresses during tightening of fasteners. It can blow a channel, thus preventing an effective seal.

The best method for lap fabrication is.

  • Assemble and drill the components. Rivets should be positioned at 50 mm spacings.
  • Separate the components and remove any drilling swarf.
  • Remove any strippable film.
  • Clean the joint.
  • Apply a continuous sealant bead as described above.
  • Relocate the components, align the holes and fasten.
  • Externally seal the centre of all rivets if required.
  • Remove surplus sealant after it has cured (not while uncured), to avoid smearing.

When placing the overlapping sheet, care should be taken to avoid disturbing the sealant when fastening.

Excess sealant should be removed with a plastic spatula or purpose made plastic scoop as excess sealant collects dirt that is unsightly.

Visible excess of sealant is not an acceptable trade practice.