Why Are UK Homes So Hot in Summer? An Architect Explains How Better Design Can Keep Your Home Cool

​For generations, British homes have been designed with one goal in mind: keeping us warm.

That made perfect sense. Research from Loughborough University has shown that, over the last 25 years, around 77 times more people have died because of cold homes than hot homes. Historically, protecting people from winter has been far more important than preparing for the occasional heatwave.

However, our climate is changing.

Longer periods of hot weather are becoming more common, and many homeowners are discovering that their homes become unbearably hot during the summer months. Bedrooms can remain above 25°C well into the night, making sleep difficult, while south-facing living spaces become uncomfortable by early afternoon.

Fortunately, good architectural design can make a dramatic difference to your comfort.

Are UK Homes Built for Hotter Summers?
In truth, most are not.

For decades, house design in the UK has focused on reducing heat loss during winter. That's why modern homes are well insulated, increasingly airtight and designed to retain warmth.

The challenge isn't that our homes are "too well insulated". In fact, good insulation is still essential for comfort and energy efficiency. The real issue is how heat enters the building in the first place and how easily it can escape afterwards.

Recognising this growing problem, the Building Regulations were updated in 2022 to include an overheating assessments for all new homes, helping ensure future developments are better prepared for warmer summers.

Why Do Some Houses Become So Hot During Heatwaves?
There isn't just one reason. Overheating is usually caused by several factors working together.
1. Solar Gain Through Windows
The biggest cause of overheating is usually sunlight entering through glazing.
Sunlight passes easily through glass and warms floors, walls and furniture inside the home. These surfaces then release the heat back into the room as infrared energy.
Unlike sunlight, this longer wavelength heat cannot easily pass back through the glass, so it becomes trapped inside the building. It's exactly the same principle that makes a greenhouse warm.
Large south, east and west facing windows can quickly turn comfortable living spaces into uncomfortably hot rooms during the summer.
2. Low Thermal Mass
Thermal mass describes a material's ability to absorb and store heat before slowly releasing it later.
Heavy materials such as brick, stone and concrete can absorb significant amounts of heat during the day, helping moderate indoor temperatures.
Lightweight construction methods don't have the same ability. Instead of absorbing heat, they warm up quickly and release that energy back into the room, allowing temperatures to rise much faster.
3. Poor Insulation
It might seem surprising, but low levels of insulation can also contribute to overheating.
Insulation doesn't simply keep heat inside during winter—it also slows unwanted heat entering from outside during summer.
A well-insulated floor, walls and loft space help reduce heat transfer into the building, keeping internal temperatures more stable throughout the day.
4. Air Leakage
Older homes often have numerous gaps where outside air can enter.
During winter this leads to heat loss. During summer, however, those same gaps allow hot external air to continually replace cooler internal air, making the house increasingly uncomfortable.
A more airtight and less drafty building, combined with controlled ventilation, allows homeowners to manage airflow much more effectively.

Why Do Older Houses Sometimes Feel Cooler?
Many people assume Victorian homes are inefficient, yet during a heatwave they can often feel surprisingly comfortable.

Victorian homes were generally built with solid brick walls both internally and externally. These heavy materials provide excellent thermal mass, helping absorb heat rather than allowing rooms to warm rapidly.

Traditional sash windows also helped. Their relatively small, portrait orientation reduced solar gain compared to many large modern windows. At night, the upper sash could be opened, allowing hot air to escape while occupants still felt secure. Many homes also featured internal shutters, often painted light colours to reflect sunlight before it entered the room.

Open chimney flues created natural stack ventilation, encouraging warm air to rise and escape.

You experience the same effect in many historic churches. Thick stone or brick walls combined with little glazing relative to the volume of the building creates remarkably cool interiors, even during the hottest days of the year.

Why Can Some Modern Homes Overheat?
Modern construction has brought many benefits, including improved energy efficiency and lower carbon emissions.

However, changing construction methods have also altered how buildings respond to heat.

Since the 1930s, windows have become cheaper to manufacture and subsequently larger, often without sufficient consideration of orientation or solar gain.

Internal walls are now frequently constructed using lightweight timber or metal studwork, while timber frame and Structural Insulated Panel (SIP) construction have become increasingly common because they are faster, more sustainable and economical to build.

These lightweight systems have a low thermal mass, meaning they cannot absorb heat in the same way as traditional masonry.

Previously, large-volume housebuilders had little reason to consider overheating because prolonged periods of extreme heat were uncommon and there was no legislation requiring them to do so. That has now changed, with overheating calculations forming part of the Building Regulations for all new build houses built since 2022.

How Can You Keep a House Cooler Without Air Conditioning?
The most effective solutions are often passive measures—design features that reduce overheating naturally before mechanical cooling is ever needed.

These include:

External Shading
Stopping sunlight before it reaches the glass is far more effective than trying to cool a room afterwards.
Solutions include:

• External shutters, widely used across southern Europe.
• Brise soleil (fixed external shading).
• Retractable awnings.
• Pergolas.
• Carefully positioned trees and planting.

Better Insulation
Improving loft insulation is often one of the simplest and most cost-effective upgrades.
External or internal wall insulation can also help regulate indoor temperatures throughout the year.

Cross Ventilation
Many commercial buildings across Europe are designed to encourage natural airflow. We can use the same principle in the design of our homes. Opening windows on opposite sides of a building allows cooler air to flow through the home while pushing warmer air out.

Where possible, homes should be designed to take advantage of prevailing winds rather than relying solely on opening a single window.

Safe Night-Time Ventilation
One of the biggest barriers to cooling homes naturally is security. Many homeowners are understandably reluctant to leave windows open overnight because of concerns about intruders, noise or pollution.

Future housing design needs to provide secure ventilation options that allow buildings to cool naturally during the night without compromising safety.

Create a Cool Retreat
Professional sporting events, such as the Nottingham Open tennis tournament, often provide cool rooms where spectators can recover from the heat on a summers day.

The same principle can work at home.

Many houses naturally have a cooler room—perhaps a north-facing ground floor room—that remains comfortable throughout the day. Using this space during the hottest part of the afternoon can make a significant difference without any building work at all.

How Will House Design Need to Change?
Architects need to design homes that respond to both winter and summer conditions.

Future homes are likely to include:

• Careful consideration of the orientation buildings on their plot.
• External shading designed into the architecture.
• Deeper roof overhangs.
• Improved cross ventilation.
• Greater use of thermal mass.
• Secure night-time ventilation.
• Landscaping that provides natural shade.
• Consideration of prevailing winds.

​Rather than relying on air conditioning, good architecture aims to prevent overheating before it occurs.

Final Thoughts
Keeping a home cool isn't simply about opening windows or buying bigger fans.

The way a building is designed has a profound impact on how comfortable it feels during the summer months.
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At JLK Architects, we believe great design should respond to how people actually live—not just today, but in the years ahead. As our climate continues to change, designing homes that remain comfortable in both winter and summer will become an increasingly important part of creating buildings that truly stand the test of time.