There’s a common misconception that external wall insulation is only useful during the colder months. Most people associate insulation with keeping the heat in — and rightly so. But have you ever thought about how it could help your home stay cooler in the summer?
As UK temperatures continue to rise and heatwaves become more frequent, overheating is becoming a real concern for many households, particularly in solid-wall homes that weren’t built with modern energy efficiency in mind. While heating costs dominate the conversation in winter, maintaining comfortable indoor temperatures in summer is just as important, and that’s where external wall insulation can make a surprising difference.
In this blog: ‘Does External Wall Insulation Work in Summer? Benefits Explained’, we’ll explore how external wall insulation works in summer, how it reduces solar heat gain, and why it’s a smart, year-round investment for energy efficiency and comfort, especially as the UK climate continues to change.
External Wall Insulation (EWI) also known as solid wall insulation is a clever system designed to improve a building’s thermal performance by attaching insulation boards to the outside of external walls. These boards, typically made from EPS, mineral wool, phenolic foam, or other insulating materials—are then covered with a reinforcing mesh, a base coat, and a decorative render finish.
While many associate insulation with benefits in colder months, fewer realise that EWI is also effective during summer. In simple terms, insulation helps retain heat in winter by reducing heat loss, while in summer, it acts as a barrier against external heat—particularly solar gain—helping to keep indoor temperatures cooler and more consistent.
How EWI Supports Year-Round Comfort
Thermal Regulation in Every Season
External wall insulation acts as a consistent thermal barrier, retaining warmth in winter and reducing heat entry in summer. This creates a more stable and comfortable indoor climate all year round.
Thermal Mass and Temperature Stability
In homes built with materials like brick or concrete, EWI works alongside the building’s natural thermal mass. These materials absorb excess heat during the day and slowly release it as temperatures drop, helping to prevent overheating and reduce indoor temperature swings.
Solar gain refers to the rise in indoor temperature caused by sunlight heating the building’s external surfaces, particularly walls and roofs. This heat is then transferred indoors, which can lead to uncomfortable indoor conditions, especially in homes without adequate insulation.
EWI isn’t just about keeping the heat in, it also helps keep unwanted heat out. In warmer months, EWI acts as a protective shield against solar gain.
Here’s how EWI reduces the impact of solar gain in summer:
With climate change bringing more frequent heatwaves and rising summer temperatures, overheating in UK homes is becoming a growing concern—especially in older solid-wall properties and retrofitted buildings.
Government regulations such as Part L (conservation of fuel and power) and Part O (overheating mitigation) now highlight the importance of managing solar gain and improving year-round energy efficiency. EWI plays a vital role in meeting these standards by helping to maintain a comfortable indoor climate in both summer and winter.
Will EWI Make My Home Too Hot?
Can EWI Be Installed in Summer?
Is Summer a Good Time to Plan for Winter Energy Savings?
Thinking about improving your home's comfort and efficiency? Get in touch with our team today for a free, no-obligation quote and expert advice tailored to your property.
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