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Background Australia has always had bushfires Their severity and frequency is increasing Urban sprawl pushes people to build in bushfire- prone areas.

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Presentation on theme: "Background Australia has always had bushfires Their severity and frequency is increasing Urban sprawl pushes people to build in bushfire- prone areas."— Presentation transcript:

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2 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?

3 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

4 Parameters that increase the destructiveness of fires 1.Temperature > 30 C 2.Wind > 20 km/h 3.Dry air (relative humidity < 30%) 4.Unstable upper atmosphere 5.Terrain 6.Vegetation 7.Building features Parameters 1-4 are not controllable by individuals My research focussed on Parameters 5-7

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

6 Assessment Criteria 1.Bushfire-resistance Non-combustible materials against AS Environmental sustainability Embodied Energy and Embodied Carbon 3.Affordability Construction costs

7 Hilly Terrain 1.Bushfire-resistance – Build on a flat block at base of a hill – Avoid building on north-facing slopes – Avoid downslopes under vegetation 2.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 3.Costs – Flat block at base of a hill reduces construction costs – Avoiding north-facing slopes increases running costs

8 Vegetation Forests - greatest risk; Grassland - lowest risk 1.Bushfire-resistance – Maximise distance between vegetation and house (Clearing allowed: Trees 10 m from house, ground fuel 30 m) 2.Environmental sustainability – Avoiding or clearing trees foregoes benefits of passive solar shading – Clearing destroys ecosystems, leads to erosion, salinity, invasive weeds and raises CO 2 levels 3.Costs – Loss of shading may increase energy costs by 30% – Tree clearing is costly

9 House shape Simple, rectangular, single-storey 1.Bushfire-resistance – Fewer ember entry points – Less surface exposed to radiant heat and flames 2.Environmental sustainability – Rectangular shape assists cross-ventilation – Cross-ventilation in a single-storey house is less effective than double-storey 3.Costs – Reduces architectural, construction and maintenance costs

10 Roofs Simple, steep, sloping away from house (Boundary: Materials, support system, battens and hardware)

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

12 Roof and exterior wall combinations 2 1

13 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 Eighteen Government-funded designs Other Option of concrete stumps with timber joists flooring Compressed fibre cement sheet decking

14 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

15 Building Standard Regulations AS modelled on temperatures 400 C lower than Black Saturdays Black Saturdays temperature was 127 C lower than possible in bushfires Test standard AS does not include effects of wind

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

17 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

18 Questions


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