As UK summers become warmer and heatwaves more frequent, overheating in homes is becoming a growing concern for homeowners, developers and designers alike. As recent UK heatwaves have demonstrated, excessive indoor temperatures can affect comfort, wellbeing and building performance.

Below are the answers to the ten questions you may be asking:

Many UK homes were designed to keep heat inside during winter, but as summers become hotter and heatwaves more frequent, keeping homes cool has become just as important. Modern homes are typically more airtight, better insulated and often include larger areas of glazing, all of which can contribute to higher indoor temperatures if heat cannot escape.

However, insulation is rarely the cause of overheating on its own. Excess heat usually enters through windows exposed to direct sunlight, builds up from appliances and occupants, or becomes trapped due to poor ventilation. The result is a home that continues to feel warm long after the outdoor temperature has dropped.

This is one of the reasons Part O of the Building Regulations was introduced, to ensure new homes are designed to reduce overheating risk while remaining energy efficient.

There is no single solution, but several simple measures can make a significant difference.

During a heatwave, homeowners should consider:

For new homes, the most effective approach is to consider overheating at the design stage. Measures such as appropriate glazing, external shading, ventilation and building orientation can help create homes that remain comfortable even during increasingly frequent UK heatwaves, while still achieving excellent energy efficiency.

Approved Document Part O is part of the Building Regulations in England and was introduced to reduce the risk of overheating in new residential buildings. Rather than focusing on keeping homes warm during winter, Part O considers how buildings perform during periods of hot weather. Designers must demonstrate that new homes limit excessive solar gains and provide sufficient means of removing unwanted heat.

Compliance can be achieved using either the Simplified Method or Dynamic Thermal Modelling (DTM), with the latter using the methodology set out in CIBSE TM59. As UK temperatures continue to rise, Part O is helping to reduce overheating risk and improve resilience in new homes throughout the year. It is important to note that Part O applies primarily to new residential buildings in England and does not generally apply retrospectively to existing homes.

Although any property can overheat during prolonged hot weather, some homes are naturally more susceptible than others.

Properties most at risk often include:

The overall design of a property, including glazing, orientation, shading and ventilation, is usually far more influential than its age alone.

Sometimes, but timing is important. Opening windows during the hottest part of the day can actually allow more warm air into your home, particularly during a heatwave. Instead, it’s generally more effective to keep windows and curtains closed while external temperatures are highest, before opening windows later in the evening and overnight when outdoor temperatures begin to fall.

Cross ventilation, where air can flow through the building from one side to another, is particularly effective at removing excess heat.

However, not every home can rely on opening windows. Noise, security concerns and poor outdoor air quality can all limit natural ventilation, which is one of the reasons these factors are considered within Part O and CIBSE TM59 overheating assessments.

Yes, but some solutions are far more effective than others. Internal blinds and curtains can reduce glare and improve comfort, but they only block sunlight after it has already passed through the glass. External shading, such as shutters, brise soleil, canopies and external blinds, prevents much of the sun’s energy from entering the building in the first place, making it significantly more effective at reducing overheating.

Solar control glazing can also help by reducing the amount of solar energy entering through windows while still allowing natural daylight into the home.

Combining shading with good ventilation is often one of the most effective ways to improve summer comfort without relying on air conditioning.

Yes. Landscaping can play an important role in reducing overheating. Trees, hedges and climbing plants can provide natural shade, reducing the amount of direct sunlight reaching windows, walls and roofs. This helps lower solar heat gains before they enter the building.

Green spaces can also help reduce the urban heat island effect, where built-up areas become significantly warmer than the surrounding countryside due to hard surfaces absorbing and releasing heat.

While planting alone will not eliminate overheating, it can form an effective part of a wider passive cooling strategy alongside shading, ventilation and appropriate glazing.

In many cases, yes. Passive design measures are often capable of reducing overheating significantly without the need for mechanical cooling.

These include:

Part O places particular emphasis on reducing overheating through passive design before relying on active cooling systems. This approach not only improves comfort but also reduces energy consumption and carbon emissions.

Our team can help you evaluate overheating risk, undertake TM59 assessments and develop practical design solutions that balance comfort, compliance and energy efficiency. Get in touch to discuss your project.

Get in Touch