•Thermal discomfort in a log house was assessed using a calibrated model.•Effective passive overheating prevention actions were identified for future climate.•Natural ventilation was the best-performing measure in reducing future overheating.•Building-related measures are of secondary importance under free-run operation.•Possibilities for future-proofing log houses are presented. This study aimed to identify the most effective passive design measures to prevent overheating in a log house in a temperate climate. The study was conducted with a calibrated thermal model under a future climate projection (SRES A2 scenario) utilising an EN 16798–1 adaptive comfort model for the building operated under free-run mode during summer. The effects of six building-related and three organisational measures on the projected future thermal comfort in the studied log house were evaluated. During 2011–2040 and 2041–2070, thermal insulation and thermal mass paired with natural ventilation with or without shading were among the best-performing combinations. During 2071–2100, three of the six best-performing combinations were thermal insulation and thermal mass paired with natural ventilation with or without shading. Comparing the first and the last periods, the most effective organisational measure reduced the operative temperature by an average of 0.35 or 0.34 °C in the first two periods and by 0.36 or 0.33 °C in the third period. By outlining the potential effectiveness of specific measures in preventing overheating discomfort under climate change conditions, the findings significantly contribute to climate change adaptation of log houses and buildings in general. These findings can be used as design guidelines for future buildings and to formulate future building regulations as well as a decision-making support for policy-makers.