Summer 2025 was the UK's warmest on record [the five hottest have all been since 2000] and the share of UK homes reporting summer overheating has quadrupled to 80% over the last decade.
The Passivhaus standard includes a strict overheating criterion: the home must spend less than 10% of the year at or above 25°C, but must aim for 0%.
Three of the most common culprits for overheating in new homes are poor ventilation, excessive unshaded glazing and heat leaking from hot water systems. The Passivhaus Planning Package software checks for all three during the design process, and designers are also required to stress-test their buildings against future climate scenarios, including situations where windows can't be opened due to pollution or noise.
The result is a home that stays comfortable, even in a heatwave.