As anyone sweltering in the current UK heatwave can attest, the country’s housing stock is woefully unsuited to heat.
Much of it is antiquated, dating from a time when the priorities were protecting from the cold and rain. Yet most new-build properties are similarly unready for experts’ predictions that, by the middle of the century, there will be temperatures on the level of summer 2018’s highs every other year.
The climate change committee warned in a report last year that more than 570,000 residences had been constructed since 2016 that were not resilient to high temperatures – and nor were a further 1.5m due to be built over the following five years.
The government advisers accused ministers of failing to act to protect people from rising temperatures that “could even leave many existing and new homes uninhabitable”.
The problem is deadly serious, as vulnerable people struggle to keep cool in their own beds. The committee noted that 2020’s heatwave in England killed more than 2,500 people, and warns that the number of heat-related deaths could triple by 2050.
Heat not only poses a threat to life but also to the structural integrity of buildings, causing walls to crack. In 2018 – the joint hottest UK summer so far alongside 1976, 2003 and 2006 – there was a spike in subsidence as the soil below buildings dried out and contracted, with more than 10,000 households subsequently making insurance claims worth £64m in just three months.
Critics accuse housebuilders, property developers and the government of being slow to respond. “The housing industry is quite traditional and old-fashioned in adapting and there are a lot of challenges that we need to deal with around zero-carbon and future-proofing,” says James Knight, of design and engineering consultancy Arcadis.
So how can the industry and country respond to the growing threat posed by high temperatures?
Retrofitting old properties
The most obvious measure to mitigate against heat is air conditioning, but it is prohibitively expensive in terms of installation and running costs, and works inefficiently in draughty older homes. The power-hungry systems also increase emissions – fuelling global heating and making the overall problem worse.
Experts suggest the UK should learn from countries where extreme heat is more usual, where homes have shutters or motorised blinds to keep out the sun and white surfaces to reflect the heat. Knight points out that around the Mediterranean, “people leave their homes shuttered all day, with the windows open behind. How many of us leave the curtains closed on south and west-facing windows when we go to work on a sunny day?”
Similar “passive measures” requiring minimal use of energy and fuel to cool homes include improving natural ventilation and increasing insulation, which has the double benefit of reducing energy bills in winter.
Designing out heat
There are even more effective measures that housebuilders can introduce at the planning and construction stage: ensuring the house and windows are oriented and positioned to limit exposure to direct sun; reducing glazing; adding shady trees and plants; and putting in an air source heat pump, which can be used to cool a home as well as heat it.
Other cooling features include windcatchers, roof-mounted devices inspired by Persian architecture that use the wind to drive fresh breezes into a room and expel stale air, and solar chimneys – tall structures with a dark surface designed to absorb solar radiation, creating a rising column of heated air that in turn keeps a ventilation system flowing.
The most advanced example of this principle is the “passive house”, an airtight, highly insulated building that relies almost entirely on passive measures such as sunshine, shading and ventilation to ensure a constant temperature. They frequently feature a ventilation unit in the attic with two air collectors: one for cool outside air and another for warm indoor air, which are circulated around the home to keep the temperature even.
“A passive house is the best solution where you have a natural flow of air through it,” says Bob Ward, deputy chair of the London Climate Change Partnership. “It should become the guide for how you build for zero carbon and overheating.”
Meanwhile Barratt, Britain’s biggest housebuilder, is trialling the Zed House, a zero carbon concept home built in partnership with 40 industry partners and the University of Salford. It has an air source heat pump and 95 sensors to gather data around the home, including on air quality. Barratt claims the pilot is the first step towards achieving its pledge that all of its new homes will be zero carbon by 2030.
What about larger buildings?
Heat is not just an issue for domestic buildings – too many offices still rely on energy-guzzling air conditioning and have large glazed facades. “Huge glass buildings are just not a good idea – that’s a greenhouse,” says Ward. “You have to design glass in a way that keeps out the sun.” A trend is now growing for installing louvre windows on commercial buildings: parallel glass slides in frames that can be tilted open or shut to improve ventilation.
Again, countries in Europe are leading the way. The Edge, a state-of-the-art office building constructed in Amsterdam for Deloitte in 2014, has been held up as an example of how to reimagine workspaces. It deploys dynamic windows, automatic shades, solar panels on the south side to keep direct sun out, underground thermal energy storage pumps to pump warm or cold water into or out of the building, and 28,000 sensors tracking movement, lighting levels, humidity and temperature.
What is the government doing?
Until now, the UK’s focus on building efficiency has been on how to improve draughty homes, especially in light of rocketing energy bills – but last year, the government added a section on overheating to building regulations for the first time, Part O, which came into effect last month. It urges housebuilders to make reasonable provision to limit solar gains in summer and “provide an adequate means to remove heat from the indoor environment”.
However, the housebuilding industry is not pleased with the new rules, complaining they could force already approved projects back to the drawing board. Stewart Baseley, the Home Builders Federation’s executive chair, wrote to the government in early June to complain that “the new regulations are riddled with impracticalities and may require tens of thousands of permissioned homes to go back through the planning process”.
And what does Ward think about Part O? “It should help although who knows how well it will be enforced,” he says.