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
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

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 Bushfire-resistance Environmental sustainability
Non-combustible materials against AS
Environmental sustainability
Embodied Energy and Embodied Carbon
Affordability
Construction costs

7. Hilly Terrain Bushfire-resistance Environmental-sustainability Costs
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

8. Vegetation Forests - 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

9. House shape Simple, 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

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

14. Eighteen Government-funded designs
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 Saturday’s
Black Saturday’s 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