Home › Upgrades › Cavity Wall Insulation
Cavity Wall Insulation: cost, savings and EPC impact
Many homes built from roughly the 1920s onwards have two layers of masonry with a gap between them. Filling that gap can cut heat loss through the walls without changing how the house looks.
IndicativeFigures on this page are indicative ranges for a typical UK home. They are not a quote, a survey or an EPC. Your home will differ.
What it is
Small holes are drilled in the outer wall, insulation is blown into the cavity, and the holes are made good. It is usually done in a day.
It is not right for every house. Walls that are exposed to driving rain, have a damaged outer leaf, or have a cavity that is too narrow or already filled can be unsuitable, and badly done insulation can cause damp.
Indicative cost, savings and EPC effect
| Typical cost | £1,000 to £2,500 |
|---|---|
| EPC points (SAP) | +3 to +9 |
| Bill saving | £100 to £300 a year |
Only suits homes with suitable, unfilled cavities. A survey checks this first.
For comparison, the Energy Saving Trust’s average installed cost for a typical semi-detached home is £2,200. See Energy Saving Trust: Retrofit explained for the latest figures.
Cavity fill can add several EPC points, particularly in a home where the walls are the main source of heat loss. See how EPC ratings work. Savings from several upgrades do not simply add up.
Is it right for your home?
- Houses with unfilled cavity walls in sound condition. Many 1930s to 1990s homes fit this description, but you cannot tell from outside alone.
- Older solid-brick or stone houses do not have a cavity. They need a different approach, and it is usually more expensive.
- Homes already filled may still be checked, because older fills can settle or degrade.
What affects the price
- Wall area and number of storeys
- Property type: detached homes have more wall than terraces
- Access, for example scaffold for high walls
- Whether an old fill has to be removed first
Questions to ask any installer
- Will you carry out a pre-installation survey, including a borescope check of the cavity?
- Will I receive a guarantee, and who stands behind it if the installer stops trading? Ask about CIGA-backed guarantees.
- Does your firm hold the right installer certification for the work?
Always get a proper survey and written quote. We introduce you to one vetted firm to do that, and explain why only one.
Related upgrades
Ready to see options for your home?
Tell us your postcode and the upgrades you are thinking about. It is free, and you are not committing to anything.
Pick your upgrades and get matched