Keeping Cool: Adapting Housing to Our Changing Climate

On Monday 12 August, many of us were sweltering on what was the UK’s hottest day so far in 2024, reaching a high of 34.8ºC in Cambridge. As our climate changes, we can expect more extremes of temperature and more heatwaves in the UK. All of the UK’s top 10 warmest years since 1884 have occurred in the 20 years since 2003. July 2022 saw the UK’s hottest ever day, with a temperature of 40.3ºC recorded in Lincolnshire that smashed the previous record by nearly 2.5ºC.

Heatwaves can cause serious problems for many different reasons. For example, the UK Health Security Agency estimated that the record temperatures across summer 2022 resulted in nearly 3000 excess heat-related deaths.  It is clear, therefore, that as we experience more frequent and more extreme periods of high temperatures in the UK in the future, adaptations will be needed to mitigate the risks to the population.

A significant area of concern is housing. The UK notoriously has some of the oldest housing stock in Europe, much of it in very poor-condition. Where UK houses are adapted to the climate, it is typically for retaining warmth in winter, rather than keeping cool in summer.

As highlighted in a recent policy paper from the University of Exeter, there is a risk that, as heatwaves become more common, homeowners in the UK will default to using active cooling solutions, such as air conditioning. The increased electricity demand from widespread adoption of air conditioning would have negative implications for the UK’s attempts to reduce its carbon emissions and would put increased strain on the electricity grid.

The policy paper therefore advocates for an emphasis on passive cooling solutions to regulate the temperature of UK housing stock. But what are these passive cooling solutions, how do they work, and are they suitable for use in typical UK housing stock?

Reducing heat load

One type of passive cooling solution is designed simply to reduce the amount of heat that buildings absorb in hot weather. These can also be some of the most straightforward solutions to retrofit to existing houses.

Thermal insulation is key. Improving insulation in the fabric of a building reduces the amount of heat that penetrates to the interior during hot weather. These approaches have the added advantage of retaining heat in winter as well, making the house warmer in winter as well as cooler in summer.

Typical measures include roof insulation, cavity wall insulation, and double (or triple) glazing. External wall insulation can also be used, particularly in older houses that lack cavity walls.

External rendering on a house can be used as a vehicle for applying wall insulation. However, an appropriate choice of render material and colour can also provide heat reflective properties. This can reduce the amount of heat absorbed by the wall, particularly if it is frequently exposed to direct sunlight.

Sunlight is a major source of heat gain in summer, particularly for houses that have a south-facing aspect. As well as heat-reflective external surfaces, increasing the available shade will reduce the heat absorbed by buildings.  Techniques to improve shading can include external window shutters or canopies, or where space allows, simply planting shady trees or bushes around the exterior of a property.

Creating microclimates

Common urban building materials such as brick and tarmac are very good at absorbing heat. This makes cities measurably warmer in hot weather than surrounding countryside.

For properties with gardens, creating your own little patch of countryside can help to bring down the temperature during extreme weather. Trees and bushes provide shade and help to reduce the amount of heat energy absorbed around the property.

In addition, plants cool their surroundings via transpiration, as water drawn up from the ground evaporates from their leaves, taking some heat with them. Vegetation also helps to capture and retain more moisture in the surrounding soil, which in turn means that the soil takes longer to heat up (due to the high heat capacity of water) and is passively cooled by evaporating water.

While these solutions are not suitable for all individual properties, they can be applied to the wider urban environment. Planting more trees and other vegetation around cities and towns, for example by building more parks and tree-lined streets, can provide shade that is essential to protect those who are out and about in hot weather. This also blocks sunlight from being absorbed by roads and nearby buildings, thereby reducing extreme temperatures during heatwaves and helping to cool the urban environment even if individual homeowners do not have the space to plant their own trees.

Ventilation

Ventilating properties can help to prevent their interiors becoming hotter than the external environment as heat gained, for example from solar radiation, is trapped inside the building. An early example of passive ventilation structures are the windcatchers discussed in our previous Insight.

Of course, installing a windcatcher on your suburban terraced house may be tricky. But an important area that can be more easily ventilated is the roof space, which can become very hot during sunny weather. Roof tiles absorb a significant amount of solar energy and, being the highest part of any house, roofs are often difficult to shade. This can lead to the roof space becoming much hotter than the outside environment. Especially if a house has poor insulation between the roof space and the living space, an overheated roof space will then transmit heat down into the house. Ventilating the roof space moves the hot air out and keeps the temperature closer to that outside, thereby reducing the heating effect on the rest of the house.

Strategic placement of fans, vents and windows can also be used to encourage ventilation through the living space. This may be particularly useful at night, when the outside temperature is likely to be lower and the accumulated heat of the day can be flushed out again by encouraging a suitable breeze.

Construction choices

Many other strategies for passive cooling are available. While some are more difficult to retrofit to existing housing stock, they may still form an important part of making future housing developments more resilient to an increasingly extreme climate.

Green roofs can be used to reduce heating of the roof due to the sun, cool the roof through evaporative cooling from the soil, and even provide additional insulation in winter.

Careful choice of the orientation of a house and the placement of its living and sleeping areas can minimise the impact of hot weather on the occupants by keeping sleeping areas cooler at night and living areas cooler during the day based on local geography and the direction of the sun.

The underlying ground can be used as a heat sink. The ground even a short distance below the surface retains a much more even temperature year-round than the air above it. Active methods include circulating air through conduits buried in the ground to cool the building’s interior, but simpler construction choices are available as well. Using concrete slabs for floors on the ground level helps to conduct heat away from the building interior and down into the ground. Such slab floors are also slower to change temperature than wooden suspended floors, helping to keep the interior temperature more stable.

Conclusions

With the UK experiencing a shortage of high-quality housing as well as a changing climate, it is clear that significant investment in housing will be needed in coming years. Innovations in technologies such as the passive cooling solutions discussed above will help to ensure that the new housing is better suited to the environmental demands of the future.

J A Kemp has specialists in all of the diverse technical fields that are involved in sustainable building technologies, from engineering to green energy and climate-tech.