Bowens has recently received reports that homeowners wishing to rebuild, or build, in bushfire areas have been advised they can only use steel in their frame construction. This is a major concern and it led me to contact Wood Products Victoria. With Boris Iskra's assistance (a representative of WPV) we set out to write a concise explanation of what can and can't be done as we re-build from the horrific events that began on 7 February. I hope the following words communicate the real story.
The new Australian Standard, AS3959-2009 Construction of buildings in bushfire-prone areas, places no specific requirements for house framing with an enclosed timber sub-floor. Builders can continue to use traditional timber framing. Keeping both embers and radiant heat out of a home is the important factor in bushfire damage prevention... whatever it is built from.
AS3959-2009 specifies timber used for construction in bushfire-prone areas should not burn readily and that "timber may be ‘bushfire resisting' by means of one or more of: the inherent properties of the material itself; being impregnated with fire-retardant chemicals; or the application of fire retardant coatings or substrates."
Some fire-retardant treated timber products have been tested to AS3959 requirements and will shortly be available on the market with fire retardant paint-on products also available. There are many hardwood options readily available to support the use of timber products in all bushfire attack levels (BALs) in the Standard, for instance:
The building requirements contained in AS 3959-2009 Construction of buildings in bushfire prone areas have been developed scientifically by experts and Australian Standards over a number of years. They are about diminishing the risk of ember, radiant heat and even flame damage. For example, enclosing the sub-floor space enables the use of traditional timber sub-floor construction.
BAL -40 and BAL-FZ require a number of external building components to comply with AS1530 testing. It is important to make sure you check compliance when ordering. These requirements, and others, are included in a table covering all external building elements and decking: Building with Timber - Construction requirements for Bushfire Attack Levels as per AS3959-2009, has been extracted from the standard. The table is available at www.timber.org.au / Design & Construction / Bushfire Performance.
TREATED TIMBER Note, when ordering ‘treated timber' it is important to make it very clear you mean timber treated with a fire-retardant, NOT timber treated with chemicals to inhibit attack by fungi and termites. The building standards for treated timbers are clear about how all treated timbers are to be identified - you need to order carefully and check deliveries to ensure the correct materials have been supplied. Bowens is ready to accommodate any and all needs in this regard.
When considering building design, a key element is preventing ember entry and subsequent ignition. With this in mind, there are some specific details that can assist in enhancing the performance of a building. These include:
Limit the fuel potential
Have a simple floor plan
Have a simple roof
Take care with outdoor rooms and decks
Consider your windows and doors
Timber doors and framing as well as timber window frames can be constructed using bushfire resisting timbers and / or combined with bushfire shutters. The materials of windows that also act as doors and doors with glass sections - will also need special consideration in some BALs. With careful planning your outlook can still be framed in timber, with its warmth, durability and special look and feel.
All new homes built in Victoria must be designed to the new bushfire standard. There are various timber solutions available for each of the bushfire attack levels with new building products and systems also being devised.
While it is important to have a compliant building design, it is equally important to consider other strategies as noted above. Ensure any vegetation surrounding the house is maintained with debris cleared, and let us pray the buildings constructed using the new standard helps us to never again witness an event such as that which occurred on those horrible days in February 2009.
For further assistance or advice on the matters above please contact Boris Iskra (Wood Products Victoria Representative) on 03 9611 9042 or Jeff Harvey (Bowens) on 0412 550 740.