Extending passivhaus to non-domestic buildings in the UK: performance under future climate variability and modelling simplification

Abstract Passivhaus is a world-leading standard for ultra-low energy, zero-carbon buildings. However, the long-term performance of such buildings under future variable climate change remains insufficiently understood. Building Performance Simulation (BPS) is a valuable tool to assess future impacts across scenarios, though workflows can be complex and time-consuming. This paper investigates whether passive building design can maintain thermal comfort and energy performance under future climate variability and evaluates the reliability of simplified BPS models in predicting these effects. The study utilises a recently constructed Passivhaus-certified non-domestic university building in Oxford, UK as case study. Three levels of modelling detail are developed following a previously established simplification framework and simulations are conducted across 12 ensemble members representing natural climate variability for two future periods (2050s and 2070s) under the highest Representative Concentration Pathway (RCP8.5) emission scenario. Results reveal cooling vulnerabilities in current Passivhaus guidance, with indoor temperatures exceeding 28 °C in extreme 2070s scenarios. Although Oxford remains heating-dominated on an annual degree-day basis, the building becomes increasingly cooling-challenged, with overheating certification thresholds met by only 8% of 2050s and 42% of 2070s scenarios. This counterintuitive difference reflects a shift from more frequent moderate threshold exceedances in the 2050s to less frequent but more severe thermal peaks in the 2070s, highlighting the limits of frequency-based overheating criteria. Furthermore, climate variability challenges single-scenario design approaches, yielding substantial ensemble spreads (± 30 MWh/month cooling, ± 1.5 maximum monthly Predicted Mean Vote). Finally, oversimplified models underestimate both summer thermal discomfort levels and variability, underscoring the need to select modelling simplification levels according to analysis objectives. Focusing on the UK context, this research proposes a framework for assessing long-term resilience of passive-design high-performance non-domestic buildings under variable climate conditions. The study aims to guide practitioners in balancing modelling detail and predictive robustness in low-energy and Passivhaus building design for climate adaptation, supporting simplified BPS methods for climate-resilient building design and evaluation.