Quick Answer: Older homes can overheat when later alterations reduce ventilation, increase solar heat gain or isolate the thermal mass of solid walls. Better shading, ventilation and carefully chosen insulation can improve comfort.
Older homes were not necessarily designed to become hot in summer. Many were built with thick solid masonry that could absorb heat and slow indoor temperature changes. Problems often appear after later changes reduce airflow, add unshaded glazing or alter how the walls manage heat and moisture. Understanding those changes is the first step towards making an older home more comfortable.
Key Takeaways
- Solid masonry can moderate indoor temperatures, but later alterations can reduce that natural benefit.
- Internal insulation can create overheating and moisture risks in some solid wall homes if it separates the room from the wall’s thermal mass.
- Shading, night ventilation and carefully designed external insulation can work together to improve summer comfort.
Why Are Older Homes More Likely to Overheat?
The age of a property is not the only issue. What matters is how the walls, ventilation, windows and later improvements interact during hot weather.
Solid Brick Walls
A solid brick wall is built as a single thickness of masonry rather than two separate leaves with a cavity between them. The masonry provides substantial thermal mass. Which means it can absorb and hold heat rather than allowing indoor temperatures to change immediately.
That can slow the rise in indoor temperature during the hottest part of the day. However, during a prolonged heatwave, the walls may not cool enough overnight.
Traditional Construction
Traditional English homes were commonly built with solid masonry walls rather than the cavity construction used more widely in later housing. Around 85% of homes built before 1919 originally had solid walls, compared with around 7% of homes built after 1965.
This matters because the original wall construction can still influence how the building responds to heat. It also means retrofit work needs to account for the way the existing building was designed to manage moisture and temperature.
Lower Thermal Performance Than Modern Homes
Older homes can have poorer overall thermal performance because of later wear, inconsistent insulation and decades of alterations. A wall may have useful thermal mass, but that does not mean the whole house will stay comfortable during hot weather.
Current English Housing Survey data shows that overheating is reported across different wall types. According to the English Housing Survey Data, of around 3 million English dwellings reporting overheating, about 2 million had cavity masonry walls and around 667,000 had solid masonry walls.
The Impact of Sun Exposed External Walls
External walls can absorb a large amount of solar heat during the day, particularly where they receive strong direct sunlight for several hours. South-facing elevations are often more exposed, although the actual effect depends on orientation, shading and the surrounding buildings.
That heat can gradually move through the wall and add to indoor heat levels. External shading, nearby trees and carefully positioned windows can reduce how much solar energy reaches the building fabric in the first place.
How Does Heat Build Up Inside an Older Home?
The main ways heat enters and builds up inside an older home are:
- Sun exposed walls absorb heat during the day.
- Roof areas and windows allow additional heat into the home.
- Solid masonry walls store some of this heat within the building fabric.
This thermal mass can be helpful when the house cools at night, because stored heat can be released and removed through cooler outdoor air. During prolonged hot weather, however, the walls may not cool enough before the next hot day begins, so heat gradually builds up.
This helps explain why construction age can affect summer comfort. National research on housing age and summer temperatures found that homes built before 1919 were significantly cooler during summer than newer housing stock.
The important factor is what happens overnight. Good ventilation and shading can help remove stored heat, allowing thermal mass to moderate temperatures rather than contributing to heat build up.
Can External Wall Insulation Help Keep Older Homes Cooler?
External wall insulation can improve summer comfort as well as winter performance when it is designed around the existing wall. The important point is not simply adding insulation, but choosing a system that works with the building’s moisture movement and thermal behaviour.
Reducing Heat Transfer Through External Walls
External insulation places the insulating layer outside the existing wall, which can reduce the rate at which heat passes between the outside and inside. It can also leave more of the masonry within the thermal envelope, allowing the wall’s thermal mass to remain part of the indoor environment.
This can be particularly useful for solid wall properties where internal insulation would separate the room from the existing masonry. Historic England guidance on insulation and overheating risk in older buildings stresses the need to consider overheating, moisture and thermal buffering together rather than treating insulation as a standalone upgrade.
Improving Thermal Comfort During Summer
Well-specified external insulation can slow unwanted heat transfer during hot weather. That can help reduce the speed at which indoor temperatures rise, particularly where the external walls receive strong solar exposure.
The benefit is not that insulation makes the house cold. It is that it can make temperature changes slower and more manageable when combined with shading and ventilation.
Year-Round Benefits for Older Properties
External insulation can also reduce heat loss during winter, so the same improvement can support comfort across different seasons. This makes it a more useful long term approach than choosing a retrofit solely around summer conditions.
The English Housing Survey found that 15% of pre 1919 homes had external insulation, while internal insulation was far more common at 46%. That difference is relevant when considering how insulation placement interacts with traditional solid wall construction.
If external insulation is suitable for your property, our external wall insulation service can be considered as part of a wider whole building retrofit plan.
How Does Spray Cork Compare with Traditional Render?
Both finishes can protect older external walls, but they suit different requirements. The main differences come down to moisture movement, thermal performance and how each finish responds to movement in the underlying wall.
| Factor | Spray Cork | Traditional Render |
|---|---|---|
| Breathability and moisture control | Vapour permeable and can allow moisture movement through the wall | Depends on the render type (with less permeable products potentially restricting moisture movement) |
| Thermal performance | Provides insulating properties that can reduce heat transfer and support steadier temperatures | Mainly provides weather protection (with less insulating value) |
| Flexibility and crack resistance | Flexible finish can accommodate minor movement in older buildings | Generally more rigid and can be more prone to cracking when the building moves |
For older solid wall properties, moisture management is particularly important. Where external insulation is unsuitable, a sprayed cork internal wall coating can provide another breathable option. The right choice still depends on the wall construction and its existing condition.
What Else Can You Do to Reduce Overheating?
The most effective ways you can reduce overheating in an older home are:
- Using external shading to limit direct sunlight reaching windows and external walls.
- Ventilating during cooler periods by opening suitable windows in the evening and early morning.
- Closing curtains and blinds during the strongest daytime sunshine.
- Reducing heat from appliances during the hottest part of the day where practical.
- Keeping internal doors open where suitable to improve airflow between rooms.
- Removing stored heat overnight by allowing cooler outdoor air to pass through the home when conditions are suitable.
These measures reduce heat entering the rooms and help remove heat stored during the day. Insulation serves a different purpose by slowing heat transfer through the building fabric.
As noted in CIBSE’s Technical Memorandum 59, assessing overheating means considering factors such as solar gains, ventilation and heat build up together. This supports a whole building approach rather than relying on one measure alone.
That matters because excessive indoor heat is not simply uncomfortable. The National Heat Risk Commission reports that UKHSA recorded 1,504 heat-related deaths in England during five heat episodes in summer 2025.
Mortality was concentrated among older adults, with significant numbers also recorded in care homes and hospitals. This reinforces the need to improve how older homes cope with prolonged heat. Most importantly where residents are more vulnerable to high indoor temperatures.
Is Spray Cork Suitable for Older UK Homes?
Spray cork can suit older UK properties where the existing walls need a breathable finish that can accommodate minor movement. The suitability depends on whether the property has solid masonry, later alterations or planning restrictions on external changes.
| Property Type | Why Spray Cork May Suit It | What to Check First |
|---|---|---|
| Victorian homes | Can suit solid masonry and traditional wall finishes | Existing coating and moisture movement |
| Edwardian homes | Can suit traditional walls with later alterations | Wall build up and previous alterations |
| Solid wall properties | Can support moisture movement while reducing heat transfer | Wall condition and existing coating |
| Conservation areas | May suit older external walls where a flexible finish is appropriate | Planning requirements for external alterations |
Before application, the wall should first be checked for defects such as cracks, damp patches, failed pointing or loose render. Any problems should be resolved beforehand, so the spray cork is applied to a sound surface rather than covering an underlying defect.
If you are considering spray cork for an older property, we can provide a professional sprayed cork service for your home.
Traditional finishes are often better suited to period homes or projects where natural materials are part of the design.
Think beyond the day the work is finished. And choose the finish that suits your home, fits your lifestyle and will still meet your needs for years to come.
FAQs
Why is my old house so hot during a heatwave?
Heat can build up through sun exposed walls, windows and roofs. Poor ventilation, added insulation and reduced overnight cooling can make it harder for that heat to escape.
Can external wall insulation help keep my home cooler?
Yes. Correctly designed external insulation can slow heat transfer while keeping more of the wall’s thermal mass within the building envelope.
Does Spray Cork reduce heat transfer?
Yes. Spray cork has insulating properties that can reduce heat transfer through a wall, although the overall effect depends on the wall and wider building design.
Why do solid wall homes overheat?
Solid walls are not automatically the cause. Overheating can result when heat enters faster than the home can release it, especially with strong solar gain and poor ventilation.
Does thermal mass make older homes hotter?
Not necessarily. Thermal mass can moderate temperatures when the building cools at night. During prolonged heat, it can store heat if overnight cooling is inadequate.
Conclusion
Older homes were not originally designed to overheat, and their solid walls can still provide useful thermal buffering. Later alterations can reduce that benefit through poor insulation choices, shading and restricted ventilation. A combination of breathable insulation, better shading and effective ventilation can improve comfort.
Get a free quote for an assessment of your property’s thermal comfort and insulation options.