TL;DR
UK homes are designed primarily for cold weather and can overheat in heatwaves. Building Regulations Part O now requires overheating mitigation in new homes. The Energy Saving Trust publishes guidance on adapting existing homes through external shading, ventilation and glazing.
UK homes are built primarily to keep heat in during winter, which means they can struggle to stay cool during summer heatwaves. Building Regulations Part O now requires overheating mitigation in new homes, and the Energy Saving Trust publishes guidance on adapting existing homes through external shading, ventilation strategies and glazing upgrades.
Why UK houses overheat
Modern UK homes are well insulated, often with airtight construction. The same features that keep heat in during winter trap heat during summer. Older Victorian and Edwardian houses have high ceilings and large windows that can help ventilation but lack shading.
South- and west-facing windows admit the most solar gain. Single glazing transmits more heat than double or triple glazing but also lets heat escape at night, which is partly why retrofitted double glazing can increase summer overheating.
Building Regulations Part O
Part O of the Building Regulations, introduced in 2022, requires overheating mitigation in new homes. Developers must show that homes are designed to limit summer heat gain and provide adequate ventilation.
Methods include external shading such as overhangs and shutters, openable windows of sufficient size, and limiting south- and west-facing glazing. Building control sign-off requires Part O compliance.
External shading and glazing
External shading is more effective than internal blinds because it stops the heat reaching the glass. Awnings, shutters and tree planting all reduce solar gain. Internal blinds and curtains help but already-warmed air sits between the glass and the room.
Solar-control glazing reflects part of the solar radiation away from the building. It works in both summer and winter and can be retrofitted to existing windows during major refurbishment. The Glass and Glazing Federation publishes performance ratings.
Ventilation strategies
Night ventilation, where windows are opened in the evening and overnight when outside air is cooler than inside, is the most effective passive cooling strategy. Cross-ventilation between opposing windows works better than single-side ventilation.
Whole-house mechanical ventilation with heat recovery, often called MVHR, is increasingly common in new builds. Summer bypass mode lets cool night air enter without preheating, helping to cool the home overnight.
When mechanical cooling is needed
Heat pumps with cooling functionality, either air source or ground source, can both heat homes in winter and cool them in summer. The upfront cost is higher than a gas boiler but lifetime running costs can be lower with renewable energy tariffs.
The Energy Saving Trust publishes guidance on selecting a heat pump that fits the home. The Boiler Upgrade Scheme provides grants for eligible installations through the Microgeneration Certification Scheme network.
Key facts
- Part O regulations require overheating mitigation in new homes.
- South- and west-facing windows admit the most heat.
- External shading is more effective than internal blinds.
- Night ventilation is the most effective passive strategy.
- Boiler Upgrade Scheme grants available for heat pumps.
FAQ
Why do UK homes get so hot in heatwaves?
UK homes are designed primarily to keep heat in during winter. The same insulation and airtight construction can trap heat during summer. South- and west-facing windows admit the most solar gain.
What is Part O of the Building Regulations?
A regulation introduced in 2022 that requires overheating mitigation in new homes. Developers must show summer heat gain is limited and that ventilation is adequate. Building control sign-off requires Part O compliance.
Are external shutters effective?
Yes, external shutters block solar gain before it reaches the glass and are significantly more effective than internal blinds. Awnings and overhangs work on the same principle.
Will a heat pump cool my home?
Air source and ground source heat pumps with reversible refrigeration cycles can both heat in winter and cool in summer. The upfront cost is higher than a gas boiler but Boiler Upgrade Scheme grants are available for eligible installations.
