The construction projects generate a significant amount of construction and demolition (C&D) waste, and part of this is due to the building defects encountered during and after the construction phase. To date, there has been no research conducted to quantitatively evaluate the impact of building defects on C&D waste generation in Australia. Thus, this research aims to quantify the waste generated by building defects to gain insights into its contribution to C&D waste generation in residential building projects in Australia. An in-depth evaluation of three case studies was conducted to analyse and quantify the waste arising from various building defects in residential building projects in Australia. A derivative of the site visit method was adopted to quantify the waste generated due to building defects in the selected case studies. This method requires investigators to visit the C&D sites for a realistic survey. The waste generated in the case studies was due to non-compliant bathroom wall tiles (CS1), incorrect roof-end capping (CS2) and flaking ceiling paint (CS3). The findings of this study revealed that non-compliant bathroom tiles have incurred a waste of 80.77 kg/m2 of wall area and a cost of $ 521.19/m2. The defect associated with the roof capping has incurred a waste of 3 kg/m of roof capping and a cost of $ 85.35/m, while the flaking of the ceiling has incurred a waste of 0.30 kg/m2 of ceiling area and a cost of $ 40.48/m2. The findings underscore the impact of building defects on waste generation, revealing critical insights into the contribution of waste generated by defects to total waste generation and the impact of such defects on the project cost. This research, thus, contributes valuable insights for builders, developers, materials suppliers and manufacturers, policymakers, and other stakeholders to adopt proactive measures aimed at minimising defects and waste generation and fostering sustainable construction practices. Furthermore, by quantitatively evaluating the impact of building defects on C&D waste generation, this research sheds light on the relationship between construction quality issues and waste production.