The hidden problem of overheating

Every year for the past four years, the Adaptation Sub-Committee (ASC) of the Committee on Climate Change has recommended to the Government that more should be done to address the growing risk of overheating in homes and other buildings. But overheating is not generally seen as a big issue compared to other climate risks, such as flooding. Why should the Government, and the public, care about overheating? There are three key reasons, says Kathryn Brown.

1. The impact on people is serious now, and will grow in the future

There are currently around 2,000 heat-related deaths in the UK each year.  Much of this increased risk is thought to be caused by exposure to high indoor temperatures. Apart from the very real human cost of this, there is also an associated economic cost. The first UK Climate Change Risk Assessment (CCRA), published by the Department for Environment, Food and Rural Affairs (Defra) in 2012, estimated that the cost from heat-related mortality due to climate change would increase from a total annual figure of £10-50 million now to between £25-150 million per year by 2050 and £40-350 million by 2080. This is classed as a ‘high magnitude’ risk according to the Government’s own criteria. Overheating risks to health also emerged as one of the top six key risks where more action is required in the most recent CCRA evidence report for Government, published by the Adaptation Sub-Committee in 2016.

Increased mortality is only one component of the effects of overheating. Illness, poor thermal comfort and reduced productivity and wellbeing are all major economic and social concerns, but there is almost no robust measurement of these impacts in the UK.

Another area of concern is the extra investment needed to retrofit homes that are already at risk from overheating. Air conditioning could be used in many instances where overheating does occur, but is expensive, energy-intensive, and expels waste heat into the environment, making the problem of overheating worse for others. It is better to avoid these costs, if possible. Research conducted by the Building Research Establishment (BRE) for the ASC’s progress report this year found that 45% of buildings professionals estimate there is ‘little or no additional cost’ of incorporating passive cooling measures in new buildings at the design stage. Design measures for homes include avoiding highly glazed south facing facades, ensuring a good ventilation to floor space ratio, external shutters, trickle vents, green roofs, and green walls covered in vegetation.

2. The risk is hidden

The majority of people are unaware that the impact from heat in terms of mortality is so high. Most of the health burden from high temperatures occurs through making existing heart or lung-related diseases worse, rather than from conditions like heat stroke. There is also likely to be low awareness that heat starts to have a negative impact on health in the UK when daily mean external temperatures exceed just 16 – 20ºC, depending on the region. To add to this, public awareness of the increasing risks from heat due to climate change appears to be very low. According to a survey conducted for Defra, more people thought that climate change would lead to colder rather than hotter weather. Although there might have been a skewed response because the survey was conducted in the winter, this is a cause for concern.

It may seem odd that overheating is an issue in a temperate country like the UK, when people cope in other, far hotter parts of the world. Part of the reason is that different populations around the world are adapted to different temperatures. But we also have a problem in the UK because, unlike in other countries, our homes and other buildings are not designed to keep us cool.  It is estimated that around 20% of homes in England already overheat in normal summer conditions, and 80% of our housing stock will still be in use in 2050. Around 90% of UK hospital wards are thought to be of a type that is prone to overheating. Work is only just starting to assess risks in care homes, but of four reviewed in a recent report for the Joseph Rowntree Foundation, all had occurrences of overheating.  There has been no work to date to systematically monitor internal temperatures in prisons or schools.

3. It is unlikely that the problem will be solved without government intervention

Overheating is caused by a market failure. Because public awareness of the health consequences of heat is low, public demand for homes that won’t overheat is also low. There are few incentives for developers to ensure overheating is mitigated in new buildings because, often, the problem won’t be apparent until after homes have been sold and people have moved in. The cost of overheating in terms of health impacts falls to the householder, not the developer.

Everybody can be affected by high temperatures, but vulnerable people are likely to suffer more; including the elderly and anyone who cannot afford to take steps to solve the problem.  The Government’s Heatwave Plan contains very useful advice on protecting vulnerable people before and during hot weather. But it is guidance; not a policy to adapt buildings to prevent the problem in the first place.

A lack of regulation was the most commonly reported barrier cited by building professionals to addressing risks of overheating in the BRE survey. A lack of skills, accountability and absence of holistic building design were also highlighted as barriers. As one respondent put it “if we mandated an overheating risk assessment, it would transform the market and would force developers to incorporate measures to manage the risk of overheating.”

There will be a renewed focus in the coming months and years on how we design and retrofit buildings in this country, in part stemming from the terrible tragedy at Grenfell Tower. A cross-sectoral effort should be made to ensure that the planning and building regulations system delivers safe, healthy, sustainable buildings – including in a changing climate.


Kathryn Brown is a Senior Analyst at the CCC’s Adaptation Sub-Committee

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