Does Insulation Work in Summer?

Insulation is often considered a way to keep your home warm in the winter. This is, of course, true – but what often gets forgotten is that it can also benefit you in the summer. But how does insulation work in the summer? We’ll explore the theories behind the concept.

How does insulation work?

Insulation slows the movement of heat between two materials. It primarily does this by trapping air within its structure—whether through dead air spaces or within the cells of the material itself. Air is a poor conductor of heat, so these trapped air pockets significantly reduce the rate at which heat can pass through the insulation.

For example, in an insulated wall, the material acts as a barrier that slows the transfer of heat from the warmer to the cooler side. On a cold day, this prevents indoor heat from escaping to the outside, helping to keep your home warm and reducing the need for additional heating. Conversely, on a hot day, insulation helps keep the cool air inside and blocks outdoor heat, making it easier to maintain a comfortable indoor temperature. However, insulation is only as effective as its installation, and one challenge in insulation is thermal bridging.

Thermal bridging

Thermal bridging occurs when a material with higher thermal conductivity (such as metal or wood) allows heat to bypass the insulation, creating a “bridge” for heat to transfer more easily from one side of a building element. This can significantly reduce the effectiveness of insulation, leading to increased heat loss or gain, depending on the season.

• Common Locations: Thermal bridges occur at structural elements such as wall studs, floor joists, window frames, and roof rafters. These elements often have lower insulation values compared to the surrounding materials.
• Impact on Energy Efficiency: Even if a wall has high-quality insulation, thermal bridges can create weak points that allow heat to escape or enter, undermining the building’s overall energy efficiency. This can lead to cold spots on walls, floors, ceilings and higher energy bills.
• Preventing Thermal Bridging: To minimise thermal bridging, builders and designers can use continuous insulation materials that cover structural elements, use advanced framing techniques that reduce the number of thermal bridges, or employ materials with lower thermal conductivity. For example, insulated cladding or external insulation systems can ‘wrap’ the building and reduce the impact of thermal bridging.

How does insulation work in the summer?

Our external wall insulation helps stop the passage of heat by trapping air bubbles within the insulating material. This means it’s easier to maintain a comfortable temperature in your home. A good demonstration of this is loft insulation. If your loft is insulated at the joist level, you will probably have noticed that it gets very cold up there in the winter. This is because the insulation is stopping your home’s heating from escaping into the loft, where it would be wasted. On the other hand, if you go up there in the summer, you’ll notice it’s hot in the loft space because hot air is coming through the roof but not getting into the main body of your home.

Although any type of insulation helps reduce air transfer, external wall insulation is the best. It stops up to 40% of heat transfer through walls – which can make a big difference. Our expanded polystyrene (EPS) boards for external insulation are made up of 98% air. This is good news because air is the best insulator when trapped and unable to move around. It creates a very difficult barrier for hot or cold air to get through.

On hot days, insulation prevents your home from overheating. The thermal mass of your walls is heated by sunlight, and the heat doesn’t pass through to the inside of your home. If you have an air conditioning system, adding a layer of external wall insulation can make it more effective. If you don’t, you can still reach a comfortable temperature by opening the windows to let in cool air at night and closing them during the day. External wall insulation will help keep this cool air inside.

The main concept behind insulation working in the summer is solar gain.

Solar gain

Solar gain refers to the increase in temperature in a space, object, or building due to solar radiation. This can be either beneficial or detrimental, depending on the climate and the time of year.

• Passive Solar Design: In colder climates, buildings are often designed to maximise solar gain, especially during the winter. This might involve large south-facing windows (in the Northern Hemisphere) that allow sunlight to enter and warm the interior spaces.
• Summer Cooling: In warmer climates or during summer, excessive solar gain can lead to overheating. Shading devices like overhangs, blinds, or reflective coatings on windows are used to prevent this.

In a well-insulated building, the effects of solar gain are more pronounced. The heat gained from the sun is retained more effectively. This can reduce heating costs in winter but may require careful management to avoid overheating in summer. The design of a building must consider the seasonal variations in solar gain. For example, using high-performance glazing that allows maximum solar gain in winter but minimises it in summer, combined with good insulation, can optimise energy efficiency. Proper ventilation is also crucial to managing solar gain and insulation. It allows excess heat to escape in the summer and helps distribute solar warmth in the winter.

Optimising solar gain

• Dynamic Shading: Adjustable shading devices can help control solar gain throughout the day and year.
• Thermal Mass: Materials like concrete or stone, which absorb and slowly release heat, can moderate indoor temperatures by storing heat during sunny periods and releasing it when the sun is not shining.
• Insulated Glazing: Double or triple glazing with low-emissivity (Low-E) coatings can reduce unwanted heat loss while allowing beneficial solar gain.

Why install external wall insulation?

External wall insulation has other benefits. Primarily, it reduces the need for air conditioning in the summer. In turn, this saves money on heating bills in the winter and makes you feel more comfortable all year round. It also helps you reduce your carbon footprint because you’ll need less heating, reduces noise entering your home, and smartens up the outside of your home.