General Principles

The details shown are not the only options; however, they represent a standard of weathering principles outlined elsewhere in this COP and are consistent with good trade practice. Deviation from the details provided would require specific approval.

Underlay must be used under metal wall cladding on lined buildings in the same manner and for the same purposes as for roof cladding.

Underlay controls condensation in an insulated cavity and offers a secondary provision to drain any ingress of moisture. For this reason, the underlay should exit at the penetration (window or door), similarly to the requirements for roof penetrations. Failure to do so can lead to the retention of moisture in the wall, with consequential corrosion of metal and the degradation of timber.

All sills should be dog-eared, or riveted, and sealed to provide a weathertight joint.

The cross section details shown can be used for vertical cladding. For horizontal cladding refer to Window Flashings (Recessed).

N.B. Head flashings are not taken to the back of the cavity as they are meant to flash the window, not the cavity. These details are similar to those supplied by WANZ WIS. 

All details should be made to allow for some air movement to dissipate condensation and without the use of sealant as the first defence against water ingress.

In high wind design load areas, all the details shown should be used in conjunction with vented closed-cell non-absorbent filler blocks fixed to the backside of the profile to baffle the wind pressure.

Filler blocks can be fixed and positioned to metal cladding by spray adhesive, in sheltered areas, however, they are not a requirement.

The design and installation of metal flashings is a crucial part of the cladding weathering process, and without detailed requirements, definitive objectives, quality checks, and known responsibility the results can be unsatisfactory and expensive to repair or replace.
Ingress of water can be insidious, and the resulting degradation of insulation, framing, and internal linings poses a threat to the health and safety of the occupants.
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