In recent years several plastic weep hole products without metal mesh have achieved compliance with AS39659:2007 via testing in accordance with in AS1530.8.1(2007).  

Here at Weepa we have some serious concerns about this trend.

1. Testing does not replicate bushfire conditions for vents and weep holes:

A wall cavity, if heated, acts as a flue or chimney, drawing air through the weep hole and upwards out of the top of the wall cavity. This airflow would cause heat and embers to be drawn into the weep hole and be held against the weep hole screen. Low melting point, injection moulded plastics are unlikely to survive these conditions.
Unfortunately AS1530.8.1 has no provision to test weep hole products by replicating these conditions. Instead they are tested as service penetrations which are sealed components of a wall system. Such testing is undertaken using wall cavities that are completely sealed, preventing all airflow and without a representative wall cavity or attached roof space. This does not replicate bushfire conditions as hot air and embers are not drawn into the weep hole.

2. Possible gaps where a product sits outside the weep hole:

Leaving aside the issue above, unless a product sits entirely within the weep hole we believe there is always a risk that embers may enter through gaps between the product and the masonry. Even where testing specifies a particular application, for example rendered or non raked brickwork, in reality most walls have imperfections and irregularities in their finish which may result in gaps larger than 3mm. Any breach in the integrity of the building envelope is a serious hazard to the building and its occupants if a bushfire does occur.

If you need to retrofit for bushfire compliance we recommend using our stainless steel product, the Protector Weep Hole Screen which sits entirely within the weephole and has been tested by BRANZ, an accredited AS1530.8.1:2018 laboratory, to meet all BAL levels up to BAL-FZ. Certificate Number FP13836-03-C1