Are code-compliant buildings ready for future climate? A case study of thermal autonomy in Australian apartments

Global climate change and rapid urbanization are intensifying urban overheating, posing challenges for cooling energy demand, thermal comfort, and human health. Apartment buildings are particularly heat-vulnerable and, as a common urban residential typology, expose many occupants to elevated indoor overheating risk. While building regulations mandate minimum performance standards, their adequacy under future climates remains uncertain. This study assesses the thermal autonomy of naturally ventilated apartment buildings in Australia under a range of climate-change scenarios. National Construction Code (NCC)-compliant buildings were compared with a reference building representing existing low-performance apartments. Future typical meteorological year (TMY) files were developed using the 4-km-resolution NARCliM2.0 regional climate modeling ensemble and compared with current TMY and extreme meteorological year (EMY) conditions for representative Sydney locations: coastal Redfern and inland Penrith. Results indicate substantial future warming across the NARCliM2.0 scenarios, with median temperatures increasing by up to 5 °C under high-emissions conditions. Despite the spread across ensemble projections, building simulations consistently show increased indoor overheating risk in both frequency and severity, especially in top-floor units. Although the NCC-compliant design improved envelope performance and reduced inter-floor variability, overheating frequency still increased from 1% to 12% in Redfern and from 10% to 23% in Penrith under the upper-bound EC-Earth3-Veg–WRF412R5 SSP3–7.0 scenario. Adaptation strategies combining envelope improvements, advanced ventilation, and external shading substantially mitigated overheating, reducing weighted exceedance hours for overly warm conditions by up to 94%. These findings highlight the need for regulatory reform to account for climate-model uncertainty and support climate-resilient apartment living under future warming.