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Background

Background. Australia has always had bushfires Their severity and frequency is increasing Urban sprawl pushes people to build in bushfire-prone areas Qn: Should houses be built in bushfire-prone areas? If so, what types of construction should be permitted?. The Critical Issues.

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  1. Background • Australia has always had bushfires • Their severity and frequency is increasing • Urban sprawl pushes people to build in bushfire-prone areas • Qn: Should houses be built in bushfire-prone areas? If so, what types of construction should be permitted?

  2. The Critical Issues • Criteria for building in bushfire-prone areas: • Bushfire-resistance • Environmental sustainability • Affordability • These criteria often conflict • Aims of study: • Identify conflicts between criteria • Provide guidance to builders by quantifying various material combinations

  3. Parameters that increase the destructiveness of fires • Temperature > 30 C • Wind > 20 km/h • Dry air (relative humidity < 30%) • Unstable upper atmosphere • Terrain • Vegetation • Building features Parameters 1-4 are not controllable by individuals My research focussed on Parameters 5-7

  4. Building Features Evaluated • Exterior Walls: • Brick Veneer • Double Brick • Hollow Concrete block • Steel • Rammed Earth • Roof: • Clay-tiled • Concrete-tiled • Steel • Living

  5. Assessment Criteria • Bushfire-resistance • Non-combustible materials against AS3959-2009 • Environmental sustainability • Embodied Energy and Embodied Carbon • Affordability • Construction costs

  6. Hilly Terrain • Bushfire-resistance • Build on a flat block at base of a hill • Avoid building on north-facing slopes • Avoid downslopes under vegetation • Environmental-sustainability • Flat block at base of a hill has minimal environmental impact • Avoiding north-facing slopes conflicts with passive solar design, increasing emissions during the use phase • Costs • Flat block at base of a hill reduces construction costs • Avoiding north-facing slopes increases running costs

  7. VegetationForests - greatest risk; Grassland - lowest risk • Bushfire-resistance • Maximise distance between vegetation and house(Clearing allowed: Trees 10 m from house, ground fuel 30 m) • Environmental sustainability • Avoiding or clearing trees foregoes benefits of passive solar shading • Clearing destroys ecosystems, leads to erosion, salinity, invasive weeds and raises CO2 levels • Costs • Loss of shading may increase energy costs by 30% • Tree clearing is costly

  8. House shapeSimple, rectangular, single-storey • Bushfire-resistance • Fewer ember entry points • Less surface exposed to radiant heat and flames • Environmental sustainability • Rectangular shape assists cross-ventilation • Cross-ventilation in a single-storey house is less effective than double-storey • Costs • Reduces architectural, construction and maintenance costs

  9. RoofsSimple, steep, sloping away from house (Boundary: Materials, support system, battens and hardware)

  10. Exterior walls (Boundary: Materials, binding medium, support system; battens, exterior render, interior plaster and paint where required)

  11. Roof and exterior wall combinations 2 1

  12. Eighteen Government-funded designs Roof • Many ember entry points • Embers roll down onto the house • Timber frame • Metal cladding Exterior Walls • Many ember entry points • Timber frame • Compressed fibre cement cladding Other • Option of concrete stumps with timber joists flooring • Compressed fibre cement sheet decking

  13. Eighteen Government-funded designs Design • 65% of house is protected from weather • Entertainment area reduces spread of fires Roof • Living roof does not fuel fire Exterior Walls • Hardwood

  14. Building Standard Regulations • AS3959-2009 modelled on temperatures 400 C lower than Black Saturday’s • Black Saturday’s temperature was 127 C lower than possible in bushfires • Test standard AS1530.8.2 does not include effects of wind

  15. Conclusions • Houses built to current building standards are unlikely to survive fires of even lower intensity than Black Saturday • AS3959-2009 and AS1530.8.2 standards are inadequate • A living roof on rammed earth walls is the best combination for fire-protection, low embodied carbon, at moderate costs

  16. Conclusions cont. • Second best choice is a living roof on double brick walls, at 21% less cost • Fire-risk, embodied carbon and costs can be reduced by building: • On a flat block at the base of a slope, away from dense forest and downslopes under vegetation • A rectangular single-storey house

  17. Questions

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