Cavities vital in exterior cladding

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For most claddings, any drained and vented cavity is formed by fi xing approximately 20mm thick battens vertically over the wall underlay to the studs to provide a free draining void or space behind the cladding. 

The only place where full length horizontal battens are used is at the top of the wall to block the top of the cavity to prevent air fl ow into the roof space, or at horizontal movement control joints to support the top of the lower sheet, provided the fl ashing bridges the cavity.

E2/AS1 does show a 5° sloped horizontal batten with 50mm gaps at each end which can be used on dwangs and also at the bottom of cladding for fixings etc, or where a horizontal fl ashing does not bridge the cavity. Proprietary perforated metal and plastic closers are available for the bottom of cavities that provide vermin control. 

Vertical corrugated sheet claddings have gaps behind the cladding that provide significant drainage and ventilation-giving benefits similar to a battened cavity. This is why vertical corrugate is able to be direct-fixed. However, horizontal profiled metal must always be fixed over a cavity. 

If the cavity batten treatment contains copper then the metal cladding must be isolated from it. This can be done adding a layer of paper-based wall underlay or strips of DPC (see fi gure 2). Alternatively you could use pre-primed battens It is vital that the wall cladding, the flashings, the cavity battens and the wall underlay are all compatible. 

Check with the cladding and underlay manufacturers that their requirements have been met. Each part of a system should have the durability which matches the specified intended life of the system.