The mercury hit 34°C in parts of southern England last week, the third heatwave this summer. For the 4.7 million UK homes with no effective shading, that means indoor temperatures above 28°C for days on end. The BBC reports that employers are now being asked whether it can be too hot to work, as reported by BBC. But the more urgent question for homeowners is: why are our houses so bad at staying cool, and what can we do about it?
Why UK homes overheat, the design flaw
British homes are built to keep heat in. Double glazing, cavity wall insulation, and loft insulation, all excellent for winter, turn a summer house into a passive solar oven. The Chartered Institution of Building Services Engineers says indoor temperatures above 26°C cause discomfort; above 28°C, health risks climb. A typical 1930s semi with south-facing windows can hit 32°C on a 30°C day. The problem is structural, not behavioural.
What it costs, and what you can save
Air conditioning is the obvious fix, but it’s expensive: a 2.5 kW unit costs £500–£1,200 to install and adds roughly £150–£250 a year to electricity bills at current Ofgem rates. Worse, it pushes carbon emissions up. Passive cooling costs a fraction of that. External blinds or awnings can reduce indoor temperatures by 5–7°C and cost £200–£600 per window. Reflective solar-control film on south-facing glazing costs about £50 per m² and cuts solar gain by 70%. The Energy Saving Trust notes that roof insulation, already subsidised under the Great British Insulation Scheme, also reduces summer heat penetration by up to 30%.
Who qualifies, and who doesn’t
The Great British Insulation Scheme covers roof and cavity wall insulation for households in EPC bands D–G. It does not cover blinds, films, or awnings. However, some local authorities run retrofit programmes that include external shading under ‘fabric-first’ measures. Check your council’s website or call the Energy Saving Trust’s home energy helpline (0800 444 202) to see what’s available in your area. Households on means-tested benefits may also qualify for a free home energy assessment under the Home Upgrade Grant.
What this misses, the EPC blind spot
Here is the catch. The current EPC methodology gives almost no weight to overheating risk. A home with triple glazing, airtight construction, and no shading can score an A for energy efficiency while being uninhabitable in July. The government’s Future Homes Standard (due 2025) will require new builds to meet overheating limits, but existing homes are left out. Until the EPC system is updated, homeowners must treat summer comfort as a separate retrofit priority, not one the market will fix for them.
What to do now: Before next summer, install reflective film on south-facing windows (under £100 for a typical bay window), plant deciduous trees on the sunny side (they shade in summer, let light through in winter), and check your loft insulation, topping up to 300 mm can cut heat gain by a fifth. If you are planning a larger retrofit, ask your installer about ‘cool roof’ coatings or green roofs. And when the next heatwave hits, close curtains on the sunny side by 10am and open windows on the shady side at night. It costs nothing and can drop the indoor temperature by 3–4°C.
Frequently Asked Questions
Not directly. The current EPC methodology does not penalise overheating risk. However, installing shading or reflective coatings can improve your home's energy performance by reducing the need for cooling, which may be reflected in the 'energy use' element of the assessment.
Not usually from national schemes like the Great British Insulation Scheme. Some local authorities include external shading in their retrofit programmes, especially if it is part of a whole-house plan. Check with your council or a certified retrofit coordinator.
