Have we made our homes too toasty?

He has done more to popularise the concept of bringing light into British homes than anyone else. “Flooding the rooms with light” is one of the best-known signifiers of his approval. 

Since the programme first launched 27 years ago, the UK has fallen in love with open-plan living and generously glazed extensions. Small, relatively easy-to-heat rooms have been combined to create one visually pleasing but, it was feared, colder, draughtier whole. As heating bills have grown and building regulations tightened, more emphasis has fallen on energy efficiency, which is often synonymous with using as much insulation as possible. 

Insulation is brilliant at keeping in warmth, which during the cold winters is a priority. But, as the UK’s winters have become wetter and milder and its summers have become longer and warmer, an unexpected problem has arisen: the overheating of homes. 

That wonderful run of bifold doors and the huge roof lantern that looked so fabulous in the architect’s render of your kitchen extension? It becomes a liability in July when it doesn’t just feel that light is flooding the room, it is as if the sun is in there with you, too. And it’s a problem that is only likely to get worse as climate change persists. 

In 2022, Approved Document O came into force, which sought to limit solar gain within new build residential properties. But these properties only account for a small fraction of British homes and, as stamp duty and other costs make moving so expensive, many people opt to renovate and reconfigure their existing homes by adding extensions that typically include a large amount of glazing 
and insulation. What can be done to tackle this problem in older buildings? “Overheating hasn’t really been considered from a retrofit perspective,” says Matthew Allcock MRICS, retrofit technical lead at Baily Garner. 

“The driver for many people has been an increased energy performance certificate (EPC) score and reduced space heating demand. This has often necessitated thick levels of external wall insulation, which does keep the heat in but also demands occupants modify their behaviour to a certain extent – they need to open windows in the summer in the early morning or at night when it is cooler, for example. They are potentially trapping a lot of heat inside during the warmer months,” he says.

Blinds alone – the usual British accommodation – simply will not tackle the issue and he points to solutions in the PAS 2035 Standard, which recommends building a generous overhang into the roofs of rooms or extensions receiving a lot of direct sunlight to prevent it entering in the first place. 

The problem, she feels, is that if ventilation is such an issue that it needs to become mechanical to keep air moving in a home, then this wipes out a lot of the reduced carbon gains of building a property that can easily be kept warm. Air conditioning guzzles energy – it is responsible for about 10% of global electricity consumption – and potentially leaks polluting hydrofluorocarbons into the environment. But it is becoming particularly necessary in apartment blocks, which, because the units are tightly packed together, are at much greater risk of overheating.

Antony Parkinson MRICS, head of block management at JLL, is well aware of the challenges of living with large windows. In 2020 he extended his own home and installed a large amount of glazing and a skylight, a measure that does lead to a certain amount of discomfort at the height of summer. “For 11 months a year it’s very pleasant so I wouldn’t change it. But it can be very, very hot for two or three weeks.”

The problem, he feels, is partly a structural one regarding the shape of many British homes: narrow but deep. “In Britain, we have the issue that we want to bring in sun during the winter, especially to the centre of an extended house that risks becoming quite dark and unwelcoming otherwise.

“It’s partly a cultural problem,” he says. “We have to have features such as trickle vents to allow some air circulation, but most people keep them closed because they fear draughts. The real issue to be concerned about is a build-up of warm damp air that condenses in, for example, the roof space.”

He believes that the British should try to learn from people already living in warmer climates. In Mediterranean countries, for example, the sun is given only a cautious welcome in the home. Shutters and windows are closed during much of the day; walls in traditional buildings are often made of very thick stone, which keeps the interior relatively cool; outside spaces are planted with shade-giving plants and have verandas, loggias and pergolas to keep the sun out of the building. However, building a veranda would mean having a plot size uncommon for most British homes and shutters are a difficult add-on as British windows open outwards. 

“In winter, you just turn your heating on and it’s fine,” Parkinson says. “However, in the summer, there is less of an escape.”

But there are some solutions and they don’t have to be especially high-tech. Parkinson has, for example, invested in a product rather like a giant shower cap that can be popped over his skylight during the summer to block out the sun. 

Mansfield says that “the key thing residents can do to help is use those cooler evening temperatures [to air their properties]”. She does, however, flag up some concern that while new build homes should have adequate thermal comfort, not all new homes will. “Part O is currently for new accommodation, but it should be brought in for change of use. I’m thinking particularly of commercial buildings such as offices, which often include a lot of glazing. 

As global warming continues to play its part in heating UK summers to temperatures that often need to be coped with rather than enjoyed, balancing thermal efficiency with cooling and ventilation strategies has come to the fore. 

We’ve spent a lot of time and effort trying to keep heat in, but we also have to let it out to prevent our homes from becoming uninhabitable when the mercury rises.