CCC- Deepening our understanding of summertime overheating in homes

By Adam Gardiner, Senior Analyst – Adaptation for the Climate Change Committee

This summer was characterised by extremes in the UK’s climate. The temperature record was smashed, exceeding 40ºC for the first time, while large parts of the country remain officially in drought.

High temperatures in homes negatively impact people’s lives. Sleep is disrupted, with knock on impacts on health and productivity. Even more seriously, high temperatures can cause illness and, in some cases, even death. Addressing the risk of overheating requires newly built houses to be constructed with a consideration of high temperatures, and that some existing homes are retrofitted to keep down internal temperatures during hot weather.

We recently invited Arup to carry out some research which looked at the extent of overheating in existing homes and the cost of limiting it. The key things we learned are:

  • A high proportion of existing homes fail to meet the new overheating standard for new homes. The majority of existing UK homes are estimated to fail the current standard used in the buildings regulations to limit overheating in new build homes. Overheating was modelled to be more prevalent in certain parts of the country such as the south of England and London, and in certain building types such as smaller dwellings such as flats. The fraction of buildings which overheat increases significantly in a warmer world.
  • Retrofitting homes to meet this standard can be achieved but would require a range of measures to be implemented by homeowners and occupants. Low-cost measures, and behavioural changes provide a first line of defence during periods of high temperatures. The study demonstrates this by showing that blinds, curtains and the opening/ closing of windows at the right time of day can be important in mitigating overheating effectively. Beyond this, a significant proportion of the stock can be cooled using only passive (e.g. external shading), rather than active cooling (e.g. air conditioning). With 2ºC of warming, passive measures, which require no energy use, can reduce overheating in up to 80% of dwellings. If we were to experience 4°C of warming however, there is a limit to the effectiveness of passive cooling.
  • Reducing overheating in homes requires significant investment. A range of measures for cooling homes were studied, the costs of which can be significant (upwards of £10,000). However, what is clearly shown in this study is the benefit of simultaneously addressing overheating and reducing emissions from buildings. Energy efficiency measures such as wall or loft insulation, if installed properly, can reduce overheating risk, whilst also reducing households’ energy use. On the other hand, if energy efficiency is installed without adequate ventilation, it can considerably exacerbate the risk of overheating.

The study has unearthed some tricky questions. Perhaps the most pressing is whether the requirement for new homes should be extended to existing homes, or a different standard developed.

There are various ways Government could use its policy tools to encourage more action here, summarised in the overheating briefing we published earlier this summer. The Government took an important first step towards managing this risk by introducing an overheating standard for new build homes this year. Whilst this is a great step forward, there remains a lack of policy to incentivise action in existing buildings.

Next year, the Government will publish its 3rd National Adaptation Programme. We are expecting to see concrete proposals for how the UK building stock will be made resilient to future climate, and public information campaigns to encourage effective behavioural change across society.

Read the full report here.