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Fire Site Design - By Vicki Boxell

by Charles Otway last modified May 07, 2014 12:50 PM
Vicki takes us through some important design tips for those planning a fire resistant property

In these days of ‘tree change’ a lot of people want to move to a forested block where the sound of the trees can sooth them to sleep and the birdsong will fill their hearts with joy. However, when an intense fire comes through many homes are in the firing line for a tragedy to occur. Poor siting, the wrong vegetation and lack of premeditation on reducing the risk of losing home and sheds can mean the loss of a lifetime’s collection. Not everyone who invests in a bush block will get a chance to decide where to place the dwelling but given the opportunity to decide where to place a house on a fire prone site here are some ideas.

 

Site selection, house design and preparing for bushfire.

The biggest issue is surrounding wooden houses by fire prone tree species.

Some would say building any house in dense bush is a recipe for disaster, no matter how well it is designed. “The Flywire House: A case study in design against bushfire” by David Holmgren on house design for fire prone sites would be well worth the investment if you decide to build somewhere that is at risk.

Given the opportunity to design for fire before you start, here are some design tips to reduce the risk by siting your home and infrastructure in the least dangerous areas on your property.

The main things to consider are prevailing winds, slope and the use of firebreaks.

 

Prevailing Winds

Sector analysis of the prevailing conditions, especially hot summer afternoon winds, will indicate where fire bearing winds are most likely to come from. On extreme fire days, hot summer winds dry out the soil and vegetation leaving it ready to flame up should ember attack occur.  Fire can travel surprisingly fast, jumping firebreaks and sending embers onto unprotected roofs and dry vegetation.  Non-flammable windbreaks and firebreaks on the windward side can prevent spreading of fire on the wind by reducing incoming radiant heat.

Slope

Fire travels uphill. The steeper the slope, the faster the fire can run up it. Placing a house at the top of a hill, then, is not a great idea. Even worse would be placing the dwelling at the top of a slope where two hills meet, looking across a valley. This could result in fire fronts approaching from two sides.

A downslope flat area is better for a home, which can be dug into the hill or placed on a mounded earth bank, then it is easy to add a pond created on the fire side of the home as a permanent firebreak. Ponds and tanks can also be used to provide a spillover of water in emergencies to help put out fires. Firebreaks at the base of a hill can reduce the intensity of a fire, hopefully stopping it getting to the hill at all.

Firebreaks or Breaking up the Fire Vegetation Available

Are a necessity and well planned ones can be used for a number of life saving emergencies, as well as a quick way around your block.  Always plan them with the idea of having more than one escape route, preferably opposite sides of the property. Roads and cleared firebreaks also provide access for the fire brigade and other emergency services.

When you are deciding where to place the house you must allow room to create a 20 metre plus circle of safety in the immediate area around the buildings where there are no flammable items. In this area large trees should not touch at the canopy or overhang the house, allowing at least 2 metres between tree and roof. Under prune trees to 2 metres to prevent grassfires setting them alight, cut back long weeds and grass and make sure there are no large groups of shrubs near the house. Removal of woodpiles, bark and sticks is also important. A non-flammable fence or wall around the outside of this space to deflect the initial heat which can dry vegetation and set it alight.

The correct sort of plant selection is really important and further information can be found on this is in PermacultureWest enews edition Summer 2013.

 

Roads, dams and non flammable vegetation, such as vegetable gardens, can be used to create breaks in flammable material. The width of firebreaks will vary depending on the soil type, local council/shire regulations are best checked in each instance. Obviously, the wider the fire break and distance between flammable areas, the better.

Other structural parts of the property can provide reduced fire risk. Homes and other infrastructure, such as sheds or silos, can be protected by areas such as orchards, non-flammable vegetative windbreaks, dams and access roads which can also create space across which fire can pass less easily.

Fire resistant shelter belts of non-flammable trees can shield a house from the initial radiant heat which dries everything before the fire front arrives.

Nearby bush or bush blocks may have high fuel loads from lack of clearing of flammable materials. Make sure these areas are cleared of dry materials and, if the fire sector is also on the side where the slope is, you will need to organise firebreaks well in advance of the dangerous season.

Allowing room for these areas when deciding where to place the house will give you more leeway for planting and placement of important structures to best protect the buildings

Conclusion

As the climate gets hotter and drier, in many parts of our state there will be higher risks of catastrophic fires. Correct house design, siting of homes and fire breaks and use of the correct plant species can do a lot towards reducing the risk of losing everything. Living in the bush needs to be thought through so that a thing of beauty and a lifetimes work can remain intact and not become a charred mess. A bit of preparation beforehand could save an awful lot of heartbreak down the track.

Disclaimer: I live in the suburbs. Do not rely on this article to save your house. Always do your own research even if you think you know something.

References

Deep Green Permaculture

http://deepgreenpermaculture.com/permaculture/permaculture-design-principles/3-each-important-function-is-supported-by-many-elements/

http://deepgreenpermaculture.com/permaculture/permaculture-design-principles/4-zones-and-sectors-efficient-energy-planning/

Department of Fire and Emergency Services (DFES) Safety Information Pages on Bushfire: http://www.dfes.wa.gov.au/safetyinformation/fire/bushfire/Pages/default.aspx

Holmgren, David, 1991. http://holmgren.com.au/product/flywire-house/