Strategies to improve the performance of openings subject to water ingress during tropical cyclones and severe storms

Abstract

Tropical cyclones and severe storms around the world generate destructive winds and heavy rain causing devastating effects to buildings. Over the years, many countries have created or improved their buildings codes after a hazard has happened. Tropical Cyclone Tracy, in 1974 devastated the city of Darwin in Australia, and after that event the Australian Building Code was significantly upgraded to ensure that building structures could withstand cyclonic wind speeds. Since then, the incidence and severity of structural failure in both normal and extreme operating conditions has reduced substantially in Australia. However, tropical cyclones and severe storms still cause repeated serviceability issues in Australia, that impact on local communities, the construction industry, the insurance industry and governments. Insurance losses due to cyclones over the past two decades in northern Australia have totalled $2.4 billion, which averages around $115 million per year. Some non-structural elements remain subject to minor failure, causing loss of amenity and damage to structural building components over time. Buildings investigations have consistently revealed that windows and external glazed doors are affected by wind-driven rain, associated with each individual storm event, causing internal leakage and subsequent damage issues such as mould, termites and infestation. Research indicates that the water ingress may not be excessive but repeated serviceability damage has a cumulative cost impact generally to building owners, insurance and government. This repeated minor to moderate damage has not been sufficiently actioned since they do not lead to structural failure or loss of life. To enhance the performance of building envelope openings subject to wind-driven rain during tropical cyclones and severe storms in the North of Queensland, the attainment of a clear understanding of the interdependencies in current practices for the entire supply chain of windows and external doors is essential. Therefore, reliable tools to predict performance of building envelope openings is essential for decision-makers to better target and prioritise investments. This aim was achieved by addressing the following three core study objectives: (1) to identify the key factors affecting the performance of window and external glazed doors to wind-driven rainwater ingress during tropical cyclones; (2) to develop an openings’ wind-driven water ingress performance prediction model; and (3) use scenario analysis to identify the most appropriate management interventions that could lead to a greater performance of window and door openings subject to wind-driven rainwater ingress during tropical cyclones and severe storms. An integrated approach was used in the study. Firstly, expert interviews and workshops were used to gain a clear insight on the entire supply chain and quality oversight of window and external glazed door installations within the Australian construction industry. This was followed by workshops to develop and operationalise a probabilistic Bayesian Network (BN) model that enabled the identification of workable strategic pathways to improve the performance of openings to mitigate water ingress during tropical cyclones and severe storms. The findings from the expert workshops and interviews revealed some key contributing fault factors and correction recommendations to improve current practices. These recommendations predominately related to upgrading practices related to documentation, inspection liability assignment and installation training for building windows and doors, especially in locations where severe winds are frequent (i.e., northern Australia) and was designed for the use of governments and industry projects. The overall research project finding demonstrates the importance of implementing a multi-pronged change to: openings standards (refers as improvements in the serviceability resistance test to water penetration), standards knowledge and training (refers to improvements in skills and knowledge of designers, builders and installers in design specification, openings installation and waterproofing practices) and in construction documentation (level of design specification). The three practices enforced together, will likely enhance the performance of building envelope openings (upgrade to 66.6% against the current condition 32.2%) and substantially reduce the likelihood that windows and door openings will experience serviceability failure during their lifespans.