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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 v23.09:Structure; Fastener-Requirements-And-Overhangs

3.9 Fastener Requirements and Overhangs 

3.9.1 Purlin-Rafter Connections 

For sprung curved roofs, the purlin/rafter connection must be increased at the eaves.

Long lengths of pierce fixed roofing will impose added loads to the purlin connection due to thermal movement of the roof.

3.9.1A Purlin to rafter fastener requirements for SG8 Radiata pine, complying with NZS 3604:2011

 Use 70 x 45 mm radiata pine on flat minimum
 Use 90 x 45 mm radiata pine on flat minimum
Rafter SpacingPurlin SpacingLow Wind ZoneMedium Wind ZoneHigh Wind ZoneVery High Wind ZoneExtra High Wind Zone
0.90.6ABCCC
0.90.9BCCCD
0.91.2CCCDD
1.20.6BCCCC
1.20.9CCCDD
1.21.2CCDN/AN/A

 

 

3.9.1B Purlin to Rafter Fastener Fixing Capacity

TypeFastenerFixing Capacity (kN)
A1/90 x 3.15 gun nails0.55
B2/90 x 3.15 gun nails0.80
C1/10g x 80 mm self-drilling screw2.40
D2.10g x 80 mm self-drlling screws3.45
E1/14 g X 100 mm self-driling screws5.50

3.9.2 Sheet Overhang 

The maximum overhang for all corrugate and low trapezoidal profiles is 150  mm, unless a product has been specifically tested to withstand point load and design wind loads at a greater overhang.

The allowable overhang distance of various cladding profiles will depend on their section properties.

When using trapezoidal profiles, greater overhangs can be achieved by stiffening the edge of the sheet in various ways; the most common being using a square gutter with a horizontal flange, but this should be fastened on every pan to achieve continuity.

The limit placed on low trapezoidal profiles with a stiffened overhang is 300 mm but it is not suitable for corrugate.

The overhang distance can be increased for some trapezoidal profiles with a rib height greater than 28 mm, but this distance must be proved by testing.

Where the cladding is fixed at a ridge or apron, the overhang distance can be increased to 250 mm from the end of the sheet, as the cladding is not subjected to the same point load or UDL and the load is shared with the flashing.

Point of access and expected roof traffic loads must also be considered.

3.9.3 Maximum Spans for Corrugate Wall Cladding 

The maximum span for pan fastened wall cladding is generally governed by temporary deflection under load, rather than permanent deflection around the fastener.

3.9.3A Maximum Span for Wall Cladding: 5 Fasteners per Sheet (every second trough)

*Serviceability load governs 
The deflection criteria used in this table is span/120 + P/20, where P = the space between fasteners. Higher deflection limits may be acceptable in certain circumstances.
Wind ZoneLoad (kPa)*Maximum Spans
0.40 mm0.55 mm
Medium0.931.802.10
High1.321.501.80
Very High1.721.401.60
Extra High2.091.201.50

3.9.4 Fastener Patterns 

Fastening patterns for the most commonly used profiles are designated in the following manner.

 

 

 

 

These fastening patterns should be used in conjunction with load span graphs.

The load on a purlin and a purlin/rafter connection is determined by the wind load and the area of roof the load is acting upon. Roof fasteners transfer wind uplift-loads to the purlins, which in turn transfer them to the primary structure.

Fastening to every second purlin may be within the roof's load/span range, but will double the load acting on the fastened purlins. All purlins must be fastened to unless alternate purlins are specifically designed to take the additional loads