Timber construction in bushfire areas

TIMBER CONSTRUCTION SAFE IN BUSHFIRE-PRONE AREAS


Building with timber is not as dangerous in bushfire-prone areas as some may believe.

A recent report by Warrington Fire Research Australia (WFRA) on the NSW bushfires in the Lower Blue Mountains has found that fire destruction of houses is due to openings allowing entry of flying embers into houses.

Openings are usually around eaves, the base of walls, or through broken glazing usually on windows that confront advancing fire. The existence of openings reduces the benefits provided through protected openings, fire resisting construction and vegetation clearance.

The report indicates that the main cause of fire destruction was entry of fire into houses due to:

 burning debris or spark access (usually though openings in eaves, ventilators, ceiling construction, or near the base of walls),
 areas where sparks and embers could accumulate,
 window glazing failure, and
 dense vegetation close to buildings allowing heat and flames to ignite elements of external construction (e.g. posts, decks)

An important design consideration for buildings in bushfire prone areas is to avoid openings to provide for greater resistance against penetration or build up of flying embers that can ignite house fires. Embers can cause ignition by contacting combustible building materials or debris, or penetrating through fragile materials

“It is also important that designers use timbers that have a suitable level of resistance to ignition or exposure to radiant heat from fire” said Phil Townsend, Deputy Executive of the National Association of Forest Industries.

There are a number of natural timber species that can be classified as fire-retardant-treated timber in accordance with Australian Standards AS 3959-1999 (Construction of buildings in Bushfire-prone Areas).

Timber species that have fire retarding qualities that satisfy the criterion for fire retardant treated timbers are Blackbutt, Kwila, Red Iron Bark, River Red Gum, Silver Top Ash, Spotted Gum and Turpentine” Mr. Townsend said.

It is anticipated that the findings of the Lower Blue Mountains report will ensure that the use of timber is not unnecessarily impeded in bushfire prone areas.

For further information visit the National Timber Development Program (NTDP) website www.timber.org.au