The role of construction standards on building impact of the 2013 Linksview Wildfire, Australia

Abstract

The 2013 Linksview fire destroyed 195 houses in the Blue Mountains of NSW in 2013. In this study, we examined the role of construction codes on the impact of houses exposed to the fire, by extracting details of construction year and standard for 466 houses from the archives of the Blue Mountains City Council.

Houses built to standards imposed from 2000 fared better than previous standards, though post-2000 houses assessed at Flame Zone level were vulnerable. Construction year was also a good predictor of impact with pre-1990 houses suffering more than twice the level of impact as post-2000 houses. Older houses tended to have more vegetation within 10 m of the house, and this probably partly explains why they are more vulnerable.

Year of modification (i.e. additions to a house) was a worse predictor than year of construction suggesting that imposing strict standards on modifications does not change the vulnerability of the whole house.

We briefly discuss four policy implications of the study: Construction standards are clearly useful; Houses in the Flame Zone are vulnerable; Lack of maintenance is a problem; and Construction Standards for building modifications do not improve the resilience of the house.

Introduction

The survivability of houses exposed to wildfires depends upon a range of factors, only some of which are controllable by residents and regulations. One of the most important and expensive is the standard of building construction. Research after bushfires has found several house construction factors to be important, including the wall and roof construction, whether the eaves are open and the type, framing and amount of window [[1], [2], [3]]. Wooden roofs have high risk [4], but there are contradictory findings about the role of roof pitches and whether elevated houses are at more risk [2,5]. The importance of the construction is reflected in the legislative regulations covering house construction in fire-prone areas. They define requirements for wall, roof and window design and materials depending on the expected level of heat exposure in order to minimise ember penetration into the house, and to maintain defensible space (e.g. Australian Standard AS3959 “Construction of buildings in wildfire prone areas” [6], the US NFPA1140 “Standard for wildland fire protection” [7] or the International Wildland Urban Interface Code [8]). These are all broadly similar in intent and implementation [9]. However, these standards are based on predictions of physical models of heat transfer rather than the empirical evidence of what actually happened in fires. A recent study of ∼200 houses destroyed in wildfires in NSW in 2013 found that aspects of house construction such as the type of wall cladding, roof and decking were less influential than the vegetation and topography around the houses [10]. That study did not directly address construction standards but highlighted the need for such an assessment. The limited direct testing of AS3959 in wildfires has found that houses built to the standard do not always survive the fire [11].

There is a need to test how well the standards perform in wildfires. To complicate matters, the standards have evolved and become stricter over the years, so that the houses exposed to any particular fire will have been built to a range of standards. In fact, in most cases, only a small proportion of the houses will have been built to the current AS3959. This evolution of the standards presents an opportunity to test whether it has been accompanied by an improvement in wildfire survival.

In Australia, owners are not required to maintain their properties to the construction standard or to retro-fit older houses, and there is no compliance monitoring to understand how well residents maintain their houses. For example, while the creation of defensible space (a fuel reduced zone 30–40 m around the house [12]) is a component of the Australian standard, there is no requirement to maintain this fuel state. This presents a significant problem because it is possible that new buildings can withstand fires well, but deteriorate over time (gradually or maybe rapidly).

Of course, house construction is only one factor influencing house loss in a wildfire, with weather, fuels, topography and householder behaviour also being important [10,13,14]. In particular, vegetation within the garden has been shown to affect house loss [10,[14], [15], [16]] and it is possible that this could compromise a building built to any standard.

In this study, we investigated the role of construction standard and building age on the impact of the Linksview fire in the Blue Mountains of NSW which destroyed 195 houses in October 2013. We test the hypothesis that stricter standards improve outcomes and that standards are a better indicator of impact than house age. We also attempt to place construction in the context of other aspects of fuel hazard by conducting statistical modelling of impact with predictors describing fuel arrangement. The results of the study provide information for policy makers as they finesse building standards across Australia, but will also be useful for other fire-prone countries, and for certifiers who implement the standards in property developments.