In recent years several plastic weep hole products without metal mesh have achieved compliance with AS39659:2009 via testing in accordance with in AS1530.8.1. Our own Weepa Pest Stoppa is one of these.
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.
Until a testing method is developed to replicate bushfire conditions in vents and weep holes under AS1530.8.1, we believe that the prescriptive requirement for metal mesh in AS3959:2009 is the only safe way to exclude sparks and embers. We are currently supporting a proposal before Standards Australia to exempt vents and weep holes from compliance under AS1530.8.1.