As climate change intensifies, heatwaves are becoming more frequent and prolonged, heightening the risk of thermal stress in indoor environments. Addressing this issue is crucial for designing buildings that can withstand such extremes and safeguard occupants’ wellbeing. This concept, known as thermal resilience to overheating, is not yet incorporated into current building design practice. This study aims to develop a comprehensive assessment framework for assessing thermal resilience, making it actionable for designers. A reference office was modelled and simulated using Modelica, incorporating uncertainties in building, system, and occupancy characteristics. A 6 days-long heatwave scenario was selected, and thermal resilience of the office with different cooling strategies was assessed based on the degree hours above an alert Standard Effective Temperature (SET) of 28 °C, with a threshold of 230 [°C.h]. A global sensitivity analysis determined regression coefficients for various building and system parameters, defining simplified regression models (TRI SET-Dh) to assess thermal resilience. These equations were validated against simulations of a case study office building in Belgium.