As homes get hotter, new research aims to tackle the issue of indoor heatwaves
Published: 12 November 2025
Ground-breaking research by the Universities of Cambridge and Glasgow has found a new way of detecting indoor mini-heatwaves and the factors influencing these.
With discussions at COP30 pushing for sustainable cooling and AI innovation, ground-breaking research by the Universities of Cambridge and Glasgow has found a new way of detecting indoor mini-heatwaves and the factors influencing these.
Europe is consistently experiencing the hottest summers on record, and understanding how we respond to heatwaves has become increasingly important. Yet traditional definitions of heatwaves (based on outdoor temperature) fail to capture how heat manifests indoors, especially in aged UK housing stock.
While only two official outdoor heatwaves occurred during the data collection period in summer of 2023, 26 of 39 households experienced at least one indoor mini-heatwave, averaging five events per home.
Extreme heat in the home can significantly impair human health and productivity, and increase cooling energy demand, leading to higher peak electricity loads and heat-related mortality.
Although there has been recognition of the overheating risks in the UK’s domestic housing stock, analysis of residents’ indoor heat exposure during heatwaves is limited.
The study aimed to address this gap by investigating the mini heatwaves occurring in domestic environments and exploring the factors influencing residents’ responses to heatwaves.
Research took place across 40 homes in London’s Southwark borough, which was recorded as one of the hottest locations in the UK in 2021. The team integrated outdoor weather data, sensor-measured high temporal-resolution indoor environmental conditions, the Index for Multiple Deprivation (IMD) and building features to analyse indoor heatwaves and thermal comfort.
The findings show that indoor temperatures lag behind outdoor ones; many mini-heatwaves continued into the evening and night (often starting at 3pm and persisting past 9pm), which overlaps with the majority time of people staying at home.
Homes with good EPC ratings or better self-reported condition overheat more often, likely because energy-efficient designs are optimised for winter insulation, but retain heat in summer.
Current UK building and retrofitting standards over-prioritise winter insulation; future policies should also consider and address summer overheating at the same time
Professor Qunshan Zhao, of the University of Glasgow’s Urban Big Data Centre, said: “With heatwaves becoming more frequent and intense, understanding how these extreme events affect indoor spaces - and the humans who occupy them - is more critical than ever. However, our one-dimensional focus on winter heating and lack of a universally accepted definition of a heatwave both pose real challenges for researchers and policymakers.
“The cooling demand for the UK homes will further increase, and the solution will need to go beyond air conditioning, which in itself is damaging to the outdoor environment. Elsewhere in the world we are seeing buildings adapted with cool roofs, urban green space, and artificial shade. Heat pumps, particularly the air-to-air heat pumps, can also be used not only to heat our homes during winter, but also to cool them during the summer. Yet there is little awareness of these solutions in the UK, and progress is frustratingly slow.
“Put simply, the UK’s housing sector is not prepared for these conditions, and we will see increased suffering as a result, unless more targeted action is taken. We hope that discussions at COP30 will address this with the urgency it deserves.”
Professor Ronita Bardhan, of the University of Cambridge, said: “Our research reveals a paradox which is critical for UK’s net-zero targets. We must recognise that carbon-efficient design is not always climate-resilient. Invisible indoor heatwaves are emerging in London’s homes, putting residents at risk long after outdoor temperatures drop. Designing for cooling resilience is now as vital as decarbonisation if we are to protect both people and the planet.”
This research study was published in Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, part of a themed issue ‘Urban heat spreading above and below ground’.
First published: 12 November 2025