COP v3.0:flashings; flashing-cover

8.3 Flashing Cover 

The weathertightness of a flashing is determined by the flashing cover, not the flashing dimension.

The minimum dimension for flashing cover (C) over profiled metal roof and wall cladding must correlate with 8.3A Minimum Dimension 'C' Flashing Cover.
There are two categories of exposure or pitch that determine the flashing cover width. Extra High Wind Zone can be extended to include wind speeds of up to 60 m/s.
Category A:
  • Low, Medium or High Wind Zones, and
  • where the pitch is no less than 10°.
 Category B:
  • Very High and Extra High Wind Zones, or
  • where the pitch is less than 10°.


This chart is relevant to trapezoidal profiles with a height of 25 – 34 mm and standard corrugate. Barge and apron flashings over profiles with a minimum 35 mm may have one rib overlap.

8.3A Minimum Dimension 'C' Flashing Cover

TYPEDirectionCategory ACategory BDrawing
RIDGETransverse over sheeting130 mm200 mm8.3B Ridge Flashing

Longitudinal trapezoidal

& tray

one ribone rib, two ribs (<20 mm) 
 Longitudinal corrugate2 corrugations3 corrugations 
 Vertically down face (smooth)50 mm75 mm 
 Vertically down face (profiled)75 mm100 mm 
APRONTransverse over sheeting150 mm200 mm8.3C Transverse Apron

Longitudinal trapezoidal

& tray

one ribtwo ribs * 
 Longitudinal corrugate2 corrugations3 corrugations 
 Vertically up face (smooth)50 mm+ hem or 75 mm75 mm + hem or 100 mm8.3C Transverse Apron
 Vertically up face (profiled)75 mm + hem or 100 mm100 mm + hem or 125 mm8.3C Transverse Apron
PARAPETVertically down face (smooth)50 mm75 mm8.3D Parapet Cap
 Vertically down face (profiled)75 mm100 mm8.3D Parapet Cap
CHANGE OF PITCHTransverse over sheet150 mm2008.4.4.2A Change of Pitch Junction Flashing
Transverse under sheet250250 


* Not to exceed 300mm.

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)

The dressed soft edging or the downturn of a notched flashing acts as a baffle to wind and rain at the outside edge of a transverse flashing, as does the stop-end of the cladding at the upper end. The void in between these two barriers acts as a pressure equalisation gap.

Pull-up stop ends must be provided for all pitches in all wind zones

In extreme circumstances, a profiled or notched closure can be used between these two baffles if required. When closures or filler blocks are used, they must be adhered to the profile or secured by the cladding fasteners to ensure they remain in position. Ventilation requirements must be considered when using profiled closures.

8.3E Barge Flashing Over One Trapezoidal Rib, Smooth Vertical Cladding

Cover two ribs with low rib trapezoidal on residential when the pitch is less than 10° and the wind zone is very high or extremely high. The face edge of a barge flashing must be attached to the fascia or wall cladding with pierce fasteners or sliding clips

8.3M 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.

8.3N Apron Upstands

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

8.3.1 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.