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| Timber and AS 3959-2009 Construction of buildings in bushfire-prone areas |
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| Friday, 10 July 2009 00:00 |
AS 3959-2009 is based on construction details appropriate for a variety of Bushfire Attack Levels (BALs). There are now five BALS: BAL-Low, BAL-12.5, BAL-19, BAL-29, BAL-40 and BAL-FZ (flame zone). The BALs are based on an assessment of the potential exposure of a site to ember attack and to radiant heat thresholds, expressed as kW/m2. For example BAL-29 is primarily concerned with protection from ember attack and from radiant heat up to and including 29 kW/m2. For brick veneer homes no special construction requirements are required by AS3959-2009 for the wall or floor frames; and as such, all commonly used timber products are appropriate for all wall studs & lintels and floor joists, bearers and flooring. Generally speaking AS3959-2009 does not impose requirements on the use of any timber that is protected from possible exposure to bushfire attack. For other unprotected building elements these general requirements in each BAL apply: BAL-LOW, the Standard does not impose any additional requirements and does not impose restrictions on the use of any timber in any element. BAL-12.5 and BAL-19 requirements can be met by the use of bushfire-resisting timber for some elements, timber with minimum seasoned density of 650 kg/m3 for some elements and timber with minimum seasoned density of 750 kg/m3 for some elements. BAL-29 requirements can be met by the use of bushfire-resisting timbers or for some elements by protecting the timber components with sarking, insulation and/or lining. Bushfire resisting timbers are defined as (when >19mm thick):
Tests are currently being conducted on additional species. Results are expected before next summer. In BAL-40 and BAL-FZ timber is permitted provided it is part of a system tested according to the method described in AS 1530.8.1 and AS 1530.8.2 respectively. There are a number of new free fact sheets and tables outlining the new Standard and how timber can be used in all the BALS available at www.timber.org.au The TDA is also currently preparing a free CPD Course to help building professionals understand AS 3959-2009 and how/where timber can be used in bushfire prone areas. |
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