Cavity wall insulation costs £800 to £1,500 for a typical semi-detached house in 2026. The price depends on wall area, insulation type, and access. Here's what you'll pay and what affects the final cost.
Cost by house type
| House type | Wall area | Typical cost |
|---|---|---|
| Mid-terrace | 40-50 m² | £600-£900 |
| Semi-detached | 60-80 m² | £800-£1,200 |
| Detached | 120-160 m² | £1,200-£2,000 |
| Bungalow | 50-70 m² | £700-£1,100 |
What's included in the cost
A typical cavity wall insulation quote includes:
- Survey and cavity width check
- Insulation material (beads, wool, or foam)
- Drilling holes in mortar joints
- Blowing insulation into the cavity
- Filling drill holes and colour-matching mortar
- CIGA 25-year guarantee
Installation takes one day for most houses. You don't need to be home during the work, but the installer will need access to the outside of the property.
What affects the price
Wall area
Installers charge per square metre or per wall. Larger houses cost more. A detached house has four external walls, so costs roughly double a mid-terrace (which has only two external walls).
Insulation type
Polystyrene beads are cheapest and most common. Mineral wool costs slightly more but has better fire performance. Foam (rarely used now) costs about the same as beads.
Access
If walls are hard to reach (steep garden, narrow side access, scaffolding needed), installers charge extra for access. Simple flat-fronted houses with easy access cost less.
Cavity width and regularity
Narrow cavities (under 50mm) or irregular cavities (partial rubble fill, common in 1930s-1940s builds) take longer to fill properly. Adds time and cost.
Free installation through ECO4
If you receive benefits or your household income is under £36,000 and your home has an EPC rating of D or below, you may qualify for free cavity wall insulation through ECO4.
Use the gov.uk Simple Energy Advice tool to check eligibility. If you qualify, contact your energy supplier to apply. See our guide on grants for insulation for details.
Getting quotes
Get at least two quotes from CIGA-registered installers. Make sure quotes include:
- Pre-install survey (checking cavity width, exposure, damp risk)
- Type of insulation to be used
- CIGA 25-year guarantee
- What's excluded (e.g. if walls need repointing first, is that included or extra?)
Don't pick the cheapest quote if it doesn't include a survey. A proper survey is essential to check your walls are suitable.
Is it worth the cost?
Cavity wall insulation saves £150 to £250 per year on heating for a typical semi. Payback is 4 to 8 years. After that, the savings keep coming for as long as you live there.
See our full guide on whether cavity wall insulation is worth it for the complete cost and benefit calculation.