Overheating housing – is it worth getting hot and bothered about?

By Dr Jonathon Taylor

Recent interviews on the BBC have described overheating in homes, particularly newer more energy-efficient homes, as a ‘public health disaster’ waiting to happen in the UK. There’s recently been a lot of research on overheating, using both field studies in people’s houses and studies that use modelling approaches. So, how serious is this problem?

Is heat a significant risk to our health?

High temperatures are known to cause several health problems, which can increase the risk of death particularly for the elderly or ill. In temperate countries, an increased number of deaths can be observed as temperatures increase above a certain threshold. In London, for example, population mortality starts to increase when the two-day average maximum temperature exceeds 24.8C, above which the increase in mortality rate (or the number of people who die each day) is around 3.8% per degree Celsius. This increases to around 5.4% in the elderly. Over a hot summer, or a heatwave, this can have serious consequences – in 2003, for example, over 2000 more deaths than usual are thought to have occurred in England and Wales due to the hot weather.

But, heat-related mortality is very small when compared to cold-related mortality in the UK, which is associated with around 30 times more deaths per year. Even under climate change scenarios, around 3 times as many people are projected to die from cold as from heat in 2080.

What is the role of housing on heat exposure?

While the relationships between temperature and mortality are derived using outdoor temperatures, people spend the majority of their time in their own homes, particularly people that are the most vulnerable to heat. So, it’s often assumed that housing can modify your exposure to higher or lower temperatures.

Housing type has been found to impact on indoor temperatures, with new builds and flats found to typically be hotter than older or detached buildings, for example. Top floor flats are particularly prone to overheating, and there was an increased risk of mortality for elderly people who lived in poorly insulated top floor flats in Paris in 2003. Certain features, such as large windows, lightweight construction, a reliance on mechanical ventilation, or indoor equipment generating heat can also act to increase indoor temperatures.

Effect of building regulations

In the interview on overheating homes, increased energy efficiency demands in building regulations, including those from the EU, have been suggested as contributing to overheating risk. Some energy efficient solutions do increase risk, for example increased building airtightness, internal solid wall insulation, and a dependence on mechanical ventilation with heat recovery rather than natural ventilation. Triple-glazed windows, if large, may be too heavy to be left wide open. But others, such as loft insulation, may help keep temperatures cooler.

But, it’s worth remembering a few things – 1) greater energy efficiency makes it easier to keep houses warm during cold weather, which is particularly important if individuals struggle to pay energy bills, 2) Increasing the energy efficiency of houses will reduce emissions, which will help slow climate change, and reduce potential exposure to future hot weather and 3) energy efficient housing is not at risk of overheating if designed appropriately.

What are the solutions?

Blaming building regulations for overheating homes is a bit of a cop out. A lot of the causes of overheating are due to design choices, such as large, inoperable, or south-facing windows, single-aspect buildings without cross ventilation, and small floor areas. So, one solution is better design which balances the need to reduce winter heating demands with summer overheating. To mitigate against overheating risk, design may include features such as low G-value windows, allowing for cross ventilation, or better occupant-controlled ventilation options. Unconventional measures such as external shutters, common in not only Mediterranean countries, but also in countries like Germany and Switzerland which are not considered to be particularly hot, have been found to be particularly effective. Another potential solution is to teach occupants, particularly vulnerable ones, how best to cope during hot weather.

So, is overheating an emerging public health issue? Given the aging population, and the increase in energy efficient housing, yes it likely will be, although I wouldn’t go so far as to describe it as a ‘disaster’. What is needed is a greater understanding of the causes and solutions to overheating, better building design which accounts for overheating risks, and potentially building regulations that incorporate heat resilience into buildings.  And while the climate looks certain to get hotter in the future, an increased focus on building design and adaptation for heat is the cool-headed response.