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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 v25.12: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 four 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 10°, 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

DimensionACategory BCD
C1130200200

200
+ baffle

Ridge TypeStandardWideWide 
     
First Purlin Position X
Pitch10°15°20°25°30°35°45°
 168167162156150143134115
 

 

8.4F Barge Flashing Cover — Trapezoidal and Secret Fixed Table


Dimension


A

Category
B


C


D

C21 upstand2 upstands2 upstands2 +
undersoaker
C1  (smooth
surface)
50757575
C1  (profiled
surface)
75100125125
 

 

8.4H Barge Flashing Cover — Corrugate Table


Dimension


A

Category
B


C


D

C22 upstands2 upstands3 upstands2 +
undersoaker
C1 (smooth)507575 75
C1 (profiled)75100125125
 

 

 

8.4J Transverse Apron Flashing Cover Table


Dimension


 A

Category
B


C


D

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

100+
hem or
125

C1 (profiled
surface)
75 +
hem or
100
100 +
hem or
125
125125
C2130200200
+ baffle
200 +
baffle
 

 

 

8.4L Apron Flashing Cover – Trapezoidal Table


Dimension


A

Category
B


 C


D

C21 upstand2 upstands*

2upstands

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

100+
hem or
125

C1 (profiled
surface)
75 +
hem or
100
100 +
hem or
125
125125
*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 upstands2 upstands3 upstands2 upstands +
undersoaker
C1 (smooth
surface)
50+
hem
or 75
75 +
hem
or 100
100 +
hem or
125
100 +
hem or
125 
C1 (profiled
surface)

75 +
hem or
100

100 +
hem or
125
125 +
hem
125 
 

 

8.4P Parapet Cap Cover Table


Dimension


A

Category
B


C


D

C1 (smooth
surface)
50757575
C1 (profiled
surface)
75100125125
 

 

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 and Minimum Slope 

E2/AS1 requires 35 mm clearance between wall cladding ends and aprons or decks, and 5mm clearance between wall cladding ends and inter-storey junctions or window head flashings, which must have a 15° slope.

In practice, the 35 mm clearance stipulation is not necessary for weathertightness or durability when the wall cladding ends are unlikely to suffer build-up on debris, which is particularly relevant where wall cladding ends above a sloping apron or a surface that is easily accessed for maintenance. In such cases, a clearance of 20 mm is sufficient to prevent contamination and prolonged wetness of the cladding.

The 5 mm clearance to inter-storey junctions and window heads is not achievable when the horizontal flashing has a slope of 15°. The clearance at the back of the flashing/roof pan should be minimal, 2 – 5 mm, and the slope of the flashing should be decreased to minimise the clearance at the rib crest. For vermin proofing, the maximum clearance at the rib should be 8 mm.

A printable bulletin is available at: BC01 Clearance between sheet ends and transverse flashings.

Extract:
"The Metal Roofing and Wall Cladding Code of Practice (COP) stipulates clearance should be provided
between the bottom edge of a profiled sheet and a transverse flashing, such as a change of pitch
flashing. The purpose of such clearance is to prevent the end of the profiled sheet from damaging the
protective coating on the flashing, due to movement of the former from thermal expansion..."

 

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,
  • unsealed laps must have a minimum cover of 150 mm, and 
  • a minimum of 100 mm cover is recommended for sealed laps to facilitate the correct alignment of two flashings.