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RE: Wind Uplift on Awning [OT: Embers in attic, etc.]

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Ralph Hueston Kratz wrote:


… instigated fire requirements that prohibited attic vents, non-fire protected decks, etc., in an attempt to minimize the disastrous effects of such features in "urban wildfire" environments.
<end quote>



Here we have AS3959:1999 Construction of buildings in bushfire-prone areas. This is a consolidation of state policies which have been introduced over the years. SA first taking steps around 1983, in the aftermath of the Ash Wednesday bushfires.


I don’t believe it prohibits vents however. There are requirements for protection of the vent: such as fine steel mesh: the mesh blocks passage of embers and otherwise, conducts heat from the embers cooling them. There are other requirements for keeping gutters clear of leaves, and for roof top sprinkler systems.


More locally, councils may impose more stringent requirements on property owners to properly management the growth of vegetation (fuel) on their properties, to keep clear off the house and provide appropriate fire breaks.


On top of that the CFS (country fire service) may also impose requirements on height and location of buildings, with respect to line of sight for their look out towers. A house on top of a hill may block line of sight, and therefore be forced to be located down the side of the hill: thus potentially changing topographic wind loading factor: which also has an influence on the behavior of an approaching fire.


Wind also drives bushfires. The wind can cause a crown-fire to jump over a cleared firebreak. Also after the Canberra bushfires, testing was done which demonstrated that steel sheet garden fencing can provide protection to property and stop the spread of ground fire. Some fires spread underground via burning root systems, and are not so dependent on the wind.


So with knowledge of localized winds, potential exists to design and develop appropriate structural barriers which can assist to contain and help reduce the spread of fires. Given our water shortage we don’t really want to be fighting fires with water. Mobile wind breaks and fire barriers could stop a crown-fire jumping a road. Also appropriate permanent structures could help divide the landscape into smaller areas, where we could allow fire to burn itself out. After all, a lot of our vegetation is dependent on fire for propagation, so we don’t really want to stop the fire, just control it.


And controlling fire in the presence of wind is a problem. Often the CFS starts a fire to burn-off vegetation and create a fire break, the wind changes direction and we end up with an out off control bushfire. Using mobile structures to create a containment area, burning off in the containment area, and then moving the structure to another area would provide greater control.


Further getting individuals to change their house to make more bushfire proof is difficult to implement. Changing the surrounding environment is therefore easier, and can be monitored by aerial photographs. And those aerial photographs used for bushfire management is how councils also identify illegal back yard construction.


So many things, so many connections.



Conrad Harrison

B.Tech (mfg & mech), MIIE, gradTIEAust



South Australia