COP v3.0:flashings; flashings-horizontal-corrugate-cladding

7.7 Flashings For Horizontal Corrugate Cladding 

Designers and contractors using horizontally fixed corrugate sheets should recognize that it needs a high standard of quality detailing and fixing and there are many requirements which different between horizontal and vertical profiled cladding.

The designers should remember that horizontal cladding produces increased shadowing and that most colours will show the accumulation of dirt. The ribs of deeper, longer spanning profiles will collect dirt both inside and outside the building, particularly on the unwashed areas of the flashings and on the underside of the ribs of outside cladding.

Insulated lined walls which are externally clad with horizontally fixed metal sheeting without a cavity should have some provision for ventilation. The better alternative is to use cavity construction.

All cladding requires maintenance, and as horizontal cladding and flashings are not self-cleaning by rain, it needs frequent washing to maintain the durability required by the NZBC, appearance and the requirements of any warranty. See 15 Maintenance .

The maintenance schedule should be provided to the owner in writing. Owners should be made aware that horizontal cladding is particularly susceptible to damage by ladders that are used without spreader bars, and it is their responsibility to notify window cleaners.


7.7.1 Fixing Horizontal Corrugate Cladding 

Because horizontal cladding emphasizes the defects in the framing line far more than vertical cladding does, the plane of both the horizontal and vertical supports should be straight within a tolerance of 5 mm in 10 m, and there should be little or no twist between the vertical and horizontal planes of framing members.

The cladding contractor should inspect and approve the standard of framing before the commencement of any cladding installation. The use of 0.40 mm coated steel cladding is likely to show any deviation in the line of the framing and 0.55 mm is, therefore, the preferred choice.

The support centres should be reduced for horizontal cladding and a minimum flashing thickness of 0.55 mm for steel or 0.9 mm for aluminium should be specified. The width of the supports will be determined by the method of jointing and secondary framework may have to be provided, with all support fixings being counter-sunk.

Fix horizontal cladding in the pan as that provides a stronger, more economical and aesthetic fastening than crest or rib fixing. The number, spacing and the position of the fasteners are determined by the wind design load for the building. See 3.14.5 Wind Load Span Graphs.

For aesthetic reasons only, or where the cladding is at eye level, the number of fasteners may have to be increased to every second corrugation for corrugated steel, and one primary fastener placed at every trough and secondary fasteners at 500 mm centres for other profiles.

A simple and aesthetically pleasing detail to join abutting lengths of horizontal cladding  is to provide a vertical break using a top hat or tee section flashing which the cladding sheets butt up to.  As this is an express detail, the sheet ends are exposed and must be cut accurately, cleanly and at a consistent length to provide a tidy looking joint.

Designers should be aware of the likelihood of condensation when horizontal metal cladding is directly fixed to a lined and insulated wall The COP recomends sealing horizontal laps with lap tape or sealant. See 7.9.5 Sealed Laps and 7.9.6 Strip Sealants.

A ventilated cavity is the preferred option. See 9.3.2 Condensation.







7.7.1D T Flashing


The COP recommends using the details in 7.7.1C Jointer Flashing when sheets exceed 8 m to allow for ease of installation and thermal expansion. Foam filler blocks are recommended for exposed sites.

Butt flashings are not a recommended detail in areas of high design wind load. External flashings should be provided instead of, or in addition to, the butt joint flashings and they should be used in conjunction with stop-ends and filler blocks.

The fasteners in horizontal cladding should be clear of the hemmed soaker and should not penetrate the flashing.

At an intersection between a horizontally clad vertical wall and a lean-to or similar at a lower level, the intersection can be flashed as shown below.



When profiled metal is used 'inside-out' as a wall cladding, it is better practice to cut the overlap back to the plane of the structure. See 7.7.1F Horizontal Cladding Lap. Penetrations in horizontal or vertical metal cladding should be installed similar to roof penetrations. For round penetrations, a proprietary boot flashing can be used. See 8 Penetrations.


The requirements for horizontally fixed cladding also apply when the cladding is used at an angle other than vertically or patterns, such as a chevron style. Where sheets are placed on an angle, the lap should be placed downside to shed the water and a soaker flashing provided to drain the run-off.