As the climate changes, cities grow denser and buildings become more ‘airtight’, there is a growing concern that our homes are more at risk of overheating, say Rob Pannell.

This can have serious consequences for the health of occupants and in extreme cases there can be a risk to life.

"In 2003 the summer heatwave across Europe is estimated to have caused the deaths of more than 35,000 people, including over 2,000 in the UK."

To better understand the scale of this problem, and propose solutions to address it, the Zero Carbon Hub is partnering with the Environment Agency, central and local government representatives and industry experts to lead the debate on overheating.

In 2003 the summer heatwave across Europe is estimated to have caused the deaths of more than 35,000 people, including over 2,000 in the UK. Although deaths associated with cold winter weather are more frequent, given that average temperatures are set to increase and that more hot spells anticipated, overheating could become more commonplace in the future.

Those most vulnerable, such as the elderly or sick, are more likely to be occupying their homes during daytime, when the heat is most intense; they will also suffer from heat disrupting their sleep at night. The challenge for both the new build and retrofit sectors going forward is to consistently provide energy efficient homes which stay comfortable throughout the year. 

Overheating comes from two sources (see also the diagram below):

External heat gains: Sun shining through the windows and heat moving through the building fabric can heat interior surfaces and air; this can be a positive contribution in the cold winter months, but may have an adverse effect if not controlled in the warmer summer months. New houses and retrofitted building stock, if inadequately ventilated, tend to retain this heat, allowing it to build up. The extent of heat gain depends, for instance, on the area of window, the home’s orientation, and whether any blinds, shades or shutters are used. In some circumstances unwanted heat can also be gained when warm external air is drawn into the home.

"The location, construction type and layout of the home can also be a factor, and overheating often arises when a number of causes or processes act together."

Internal heat gains: Internal gains can vary depending on the type or age of the home. For recent homes, which are more airtight and better insulated, heat gains from internal sources may have a significant effect. It may arise from occupants themselves, building services such as hot water systems, and lighting and appliances.

The location, construction type and layout of the home can also be a factor, and overheating often arises when a number of causes or processes act together. For example, in cities the presence of the ‘heat island effect’ – where air temperatures can remain high even night – can make purging hot air particularly problematic.

One difficulty of addressing this problem is being able to define what constitutes overheating. The issue arises because it is difficult to agree what constitutes ‘too hot’, because it differs from person to person and depends on other factors such as external temperature, humidity, duration and an individual’s susceptibility. The relationship between external and internal temperatures is also highly variable. 

There are also a number of practical challenges around overheating.  These include planning issues, such as whether plannning permission can be agreed for measures affecting the outward appearance of buildings. It is also clear the design of individual homes has a huge impact on the risk of overheating through the orientation thermal mass, shading, and cooling and ventilation strategies. Finally, the behavior of the building’s occupants – in particular, how they use the ventilation systems, shading and windows - affects conditions in the property. 

The main aim of the Zero Carbon Hub’s major new project will be to evaluate a number of options for supporting and incentivising action by housing providers to tackle overheating , ranging from improving tools and guidance, through to mandatory legal standards.

Crucially, government, the housebuilding industry and those involved in managing existing homes are closely engaged in the project to ensure all proposals are both practical and commercially viable.

Rob Pannell is the MD of the Zero Carbon Hub

To learn more about this project and the Hub’s other work, please visit www.zerocarbonhub.org.