Designers tend to focus on winter performance first and foremost since this is where the greatest energy savings are to be made (in northern Europe at least), but focusing on winter performance alone can result in severe overheating problems in well-insulated buildings, even in northern Scotland! Overheating is a problem for comfort, energy use (because people tend to install summer cooling) and health, and this problem is likely to get worse in a warming world. This needn’t be the case. Well-designed, low-energy buildings should perform better in both summer and winter than traditional buildings. I provide detailed overheating analysis for new building designs and proposed retrofits to ensure they perform well all year round. Future climate scenarios can be incorporated into this analysis to account for anticipated global warming.