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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:Flashings; Flashing-Cover

8.4 Flashing Cover 

The weathertightness of a flashing is determined by the flashing cover (C), not the flashing dimension.(D)  Other considerations are catchment area, wind exposure, roof pitch and profile height.

The minimum flashing cover (C) must correlate with the tables below.

There are three categories of exposure or pitch that determine the required flashing cover  .

Category A:

  • Low, Medium or High Wind Zones, all pitches
  • Very High and Extra High Wind Zones where the pitch is equal to or greater than 10°.

Category B:

  • Very High where the pitch is less than 8°, and
  • Extra High Wind Zones all pitches. 

Category C:

  • SED Wind Zones up to 60 m/s, all pitches.

Category D:

  • SED up to 68 m/s, all pitches.

NOTE: These tables are relevant to trapezoidal profiles with a rib height of 20 – 34 mm and standard corrugate. Longitudinal flashings over profiles with a rib height greater than 34 mm may have one rib overlap 

8.4D  Ridge and Head Flashing Cover Table


Dimension


A

Category
B


C


D
C1130 mm200 mm200 mm
 
200 mm
+ baffle
Ridge TypeStandardWideWide 
     
Purlin Position X    
Pitch 8°–15°165 mm150 mm150 mm150 mm
Pitch 15°–30°150 mm200 mm200 mm200 mm
Pitch 30°–45°130 mm180 mm180 mm180 mm
 

 

8.4F  Barge Flashing Cover — Trapezoidal and Secret Fixed Table


Dimension


A

Category
B


C


D

C21 rib2 ribs2 ribs2 +
undersoaker
C1  (smooth
surface)
50 mm75 mm75 mm75 mm
C1  (profiled
surface)
75 mm100 mm125 mm125 mm
 

 

8.4H  Barge Flashing Cover — Corrugate Table


Dimension


A

Category
B


C


D

C22 crests2 crests3 crests2 +
undersoaker
C1 (smooth)50 mm75 mm75 mm 75 mm
C1 (profiled)75 mm100 mm125 mm125 mm
 

 

 

8.4J  Transverse Apron Flashing Cover Table


Dimension


 A

Category
B


C


D

C1 (smooth
surface)
50 mm +
hem or
75 mm
75 mm +
hem or
100 mm
100 mm +
hem or
125 mm

100 m +
hem or
125 mm

C1 (profiled
surface)
75 mm +
hem or
100 mm
100 mm +
hem or
125 mm
125 mm125 mm
C2130 mm200 mm200 mm
+ baffle
200 mm +
baffle
 

 

 

8.4L  Apron Flashing Cover – Trapezoidal Table


Dimension


A

Category
B


 C


D

C21 rib2 ribs*

2 ribs

2 ribs +
undersoaker
C1 (smooth
surface)
50 mm +
hem
or 75 mm
75 mm +
hem
or 100 mm
100 mm +
hem or
125 mm

100 mm +
hem or
125 mm

C1 (profiled
surface)
75 mm +
hem or
100 mm
100 mm +
hem or
125 mm
125 mm125 mm
*Not to exceed 300 mm. Two ribs cover can consist of two machined crests or one machined crest plus an upstand, hand-formed from the adjacent pan.

 

 

8.4N  Apron Flashing Cover – Corrugate Table


Dimension


A

Category
B


C


D

C22 crests2 crests3 crests2 +
undersoaker
C1 (smooth
surface)
50 mm +
hem
or 75 mm
75 mm +
hem
or 100 mm
100 mm +
hem or
125 mm
100 +
hem or
125 mm
C1 (profiled
surface)

75 mm +
hem or
100 mm

100 mm +
hem or
125 mm
125 mm +
hem
125 mm
 

 

8.4P  Parapet Cap Cover Table


Dimension


A

Category
B


C


D

C1 (smooth
surface)
50 mm75 mm75 mm75 mm
C1 (profiled
surface)
75 mm100 mm125 mm125 mm
 

 

8.4R  Change of Pitch Flashing Cover Table


Dimension


A

Category
B


C


D

C1
250 mm250 mm300 mm300 mm
C2150 mm200 mm200 mm200 mm +
baffle
 

8.4.1 Apron Upstands 

The minimum cover of the upstand of an apron flashing varies depending on whether the upstand is hemmed or unhemmed, and whether the covering cladding is smooth or profiled. Profiled claddings require more coverage because they allow vertical air movement through the voids of the profile.

 

 

 

8.4.2 Clearances 

The end of wall cladding should have a minimum clearance of 25 mm from an apron flashing or another horizontal surface. Where vegetation is present, or debris may accumulate, greater clearances or regular maintenance is required to achieve optimum durability. See 4 Durability.

8.4.3 Ridging and Other Transverse Flashings 

A soft edge or notched flashing must be provided to transverse flashings. The positioning of the top purlin must be adjusted with the pitch and the ridge girth to ensure that primary fastening is provided between 15 mm and 50 mm from the leading edge of the flashing. See 8.4C Ridge and Head Flashing Cover.

8.4.4 Flashing Laps 

Laps in flashings should comply with the following criteria:

  • Water must flow over a lap, not into it,
  • a lap must not rely solely on sealant,
  • sealed laps must be mechanically fixed at 50 mm centres, and
  • end laps must be a minimum of 150 mm for unsealed laps and 100 mm for sealed laps.