Risk assessment and mitigation for Australian contemporary houses subjected to non-cyclonic windstorms

Non-cyclonic windstorm is a major natural peril that causes substantial economic losses to housing in New South Wales, Victoria and south-eastern Queensland where the majority of Australia’s population live. Housing in non-cyclonic regions of Australia comprises a large portion of metal-clad contemporary houses with complex hip-roof geometries. According to post-damage surveys, wind-induced losses to Australian contemporary houses mainly result from direct wind damage to roof and windows as well as associated rainwater damage to building interior and contents. Construction defects have also been observed as a major contributor to housing damage during windstorms. There is a lack of systematic approaches to assess wind and rainfall losses for metal-clad contemporary houses in non-cyclonic regions of Australia with an explicit modelling of construction defects. Risk mitigation and climate adaptation aim to improve building resilience to wind hazards and reduce economic losses associated with wind damage under a changing climate. Although several mitigation/adaptation measures for Australian housing have been proposed in the literature, quantitative evaluations of their cost-effectiveness are still limited. There is a need for a quantitative decision support model to assist relevant decision-makers and stakeholders in choosing appropriate mitigation/adaptation measures for the protection of houses against wind hazards. This PhD research develops a probabilistic risk assessment (PRA) and decision support framework for metal-clad contemporary houses subjected to non-cyclonic windstorms. The PRA framework integrates hazard modelling for extreme wind speed and associated rainfall, reliability-based wind damage assessment for roof system and windows, rainwater intrusion evaluation and economic loss estimation. A probabilistic construction defect model including five types of defects in roof connections is also developed, which can be readily integrated into the PRA framework to account for the reduced roof reliability and performance due to defective roof components. A scenario-based approach is adopted to include climate change impact on extreme wind speed and associated rainfall. The developed PRA framework is illustrated on representative metal-clad contemporary houses in two Australian cities − Brisbane and Melbourne (i.e. capital cities in Queensland and Victoria). Risk-based decision models are employed to provide decision support to identify cost-effective measures for risk mitigation and climate adaptation. The magnitude of uncertainty and decision-makers’ risk preferences (i.e. risk aversion, risk-neutrality and risk proneness) are taken into account in the decision-making. The implications for mitigation/adaptation decisions with the consideration of insurance and economic incentives are also discussed. The PRA and decision analysis results suggest that rainwater damage to building interior and contents is a major contributor to economic risks for Australian contemporary houses subjected to non-cyclonic windstorms. Installing window shutters is a promising mitigation/adaptation measure for homeowners in Brisbane to implement. Climate change has a marginal influence on the cost-effectiveness of mitigation/adaptation measures. The outputs of this PhD research can assist insurance and re-insurance industries in catastrophe risk management, government agencies in disaster planning and management, and homeowners in choosing cost-effective mitigation/adaptation measures to protect their home against windstorms. This research paves the way towards a more resilient residential community under wind hazards.