The number of houses at risk from wildfire continues to increase around the world as populations continue to expand into fire-prone areas. Creating defensible space (managing fuels within a 30-m zone around a house) is a key strategy for mitigating risk, but there is a need to evaluate the key components of defensible space. This study examined house impact in 27 independent forest fires from New South Wales, Australia, between 2001 and 2009, comprising 309 houses destroyed or damaged and 618 unburnt houses. A range of spatial measures of vegetation, nearby buildings, waterbodies and topography were measured around each house. Principle Components Analysis and Generalised Additive Mixed Model analysis was used to derive the best and supported alternative models to explain the determinants of housing impact. The best model contained positive effects of vegetation touching the house and estimated Radiant Heat Flux and negative effects of distance to the nearest building and the number of nearby waterbodies on the probability of impact. The results suggest that risk could be effectively reduced by providing waterbodies, maintaining defensible space and ensuring separation between houses.