Bushfire Compliance (AS3959:2009)

A Guide to Weep Holes in Bushfire Prone Areas

In response to devastating bushfires in Victoria in 2009, Australian Standard 3959 was updated and republished AS3959:2009. The Building Code of Australia referenced the new Standard on the 1st May 2010. The old standard had 4 levels of bushfire attack, the new Standard has 6 levels of severity expressed as Bush-fire Attack Levels (BAL).

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Bushfire Attack Levels

AS3959:2009 is primarily concerned with improving the ability of buildings in designated bushfire prone areas to better withstand attack from bushfire, thus giving a measure of protection to the building occupants (until the fire front passes) as well as to the building itself.

Research is continuing with regards to the effects of bushfires on buildings, determination of bushfire prone areas within various States and particular construction techniques designed to maximize the performance of buildings when subjected to bushfire attack. The outcomes of this research will be reflected in subsequent editions of AS3959.

BAL - Low 
There is insufficient risk to warrant specific construction requirements.
BAL - 12.5 
Ember attack.
BAL - 19 
Increasing levels of ember attack and burning debris ignited by wind-borne embers together with increasing heat flux between 12.5 and 19 kW m2. 
BAL - 29 
Increasing levels of ember attack and burning debris ignited by wind-borne embers together with increasing heat flux between 19 and 29 kW m2. 
BAL - 40 
Increasing levels of ember attack and burning debris ignited by wind-borne embers together with increasing heat flux with the increased likelihood of exposure to flames. 
BAL - FZ 
Direct exposure to flames from fire front in addition to heat flux and ember attack.

Summary of Weep Hole Requirements

BAL - Low 
There are no special requirements for weepholes.
BAL - 12.5 
Clause 5.4.3 Amdt 3-2011 "Vents and weepholes in external walls shall be screened with a mesh with a maximum aperture of 2mm, made of corrosion-resistant steel, bronze or aluminium, except where the vents and weepholes have an aperture less than 3mm (see clause 3.6), or are located in an external wall of a subfloor space."
BAL - 19
Clause 6.4.3, Amdt 3-2011 "Vents and weepholes in external walls shall be screened with a mesh with a maximum aperture of 2mm, made of corrosion-resistant steel, bronze or aluminium, except where the vents and weepholes have an aperture less than 3mm (see clause 3.6), or are located in an external wall of a subfloor space." 
BAL - 29
Clause 7.4.3 Amdt 3-2011 "Vents and weep holes in external walls shall be screened with a mesh with a maximum aperture of 2mm, made of corrosion-resistant steel, bronze or aluminium, except where the vents and weep holes have an aperture less than 3mm (see clause 3.6), or are located in an external wall of a subfloor space."
BAL - 40
Clause 8.4.3 "Vents and weepholes in external walls shall be screened with a mesh with a maximum aperture of 2mm, made of corrosion-resistant steel, bronze, except where the vents and weepholes have an aperture less than 3mm (see clause 3.6)" 
BAL - FZ
Clause 9.4.3 "Vents and weepholes in external walls shall be screened with a mesh with a maximum aperture of 2mm, made of corrosion-resistant steel, bronze, except where the vents and weepholes have an aperture less than 3mm (see clause 3.6)"

This information is a guide for the different construction requirements for weep holes in each level. It is not a replacement for AS 3959:2009. For more information refer to AS 3959:2009 Construction of Buildings in Bushfire Prone Areas which is available from SAI Global. For specific project advice always consult your Building Certifier.

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The Weepa range is subject to Intellectual Property Rights: Aust Pat Nos - 713335, 762230, 2007237177, 2007215369, 2008271915  Aust Pat Aps - 2013211506. International PCT AU2007/000004, PCT AU2014/000123.  NZ Pat No 567674, Sth Africa Pat No 2008/03841, USA Pat No 8171677, Canada Pat No 2629033, Germany Pat No 602007037097.3, Spain Pat No ES2491221, Italy Pat No IT1984580, France Pat No FR1984580, United Kingdom Pat No GB1984580. Des Reg 137021, 150609, 156915. Aust TM 775282, NZ TM 961710, USA TM 4457028, Europe TM 1145302.