Cavity Wall Insulation Cost UK (2026)
Last updated 5 October 2026 · Prices based on the Ofgem price cap (October 2026 – December 2026)
Insulation is blown into the gap between the inner and outer walls through small holes, which are then filled. It takes about half a day for most houses and causes little disruption.
Cavity wall insulation cost payback calculator
At £1,800 net cost and £350 saved a year, it pays for itself in about 5.1 years.
- Net cost
- £1,800
- Payback
- 5.1 yrs
- 10-year saving
- £1,700
Simple payback = (cost − grant) ÷ annual saving, at today's price cap (26.32p electricity, 7.97p gas). Ignores future price changes.
Cavity wall insulation cost by property type
| Property type | Typical cost | Annual saving | Payback |
|---|---|---|---|
| Flat | £700–£1,000 | £120–£160 | 5–7 yrs |
| Mid-terrace | £1,000–£1,400 | £180–£230 | 5–6 yrs |
| Semi-detached | £1,500–£2,000 | £300–£380 | 4–6 yrs |
| Detached | £2,000–£2,500 | £420–£480 | 4–6 yrs |
What affects the cost
Wall area
Detached homes have more exposed wall.
Material
Mineral wool, EPS beads or polyurethane foam.
Exposure
Homes facing driving rain may need extra checks.
Access
Scaffolding is rarely needed but adds cost if it is.
Existing problems
Damp or failed old insulation must be removed first.
How to reduce the cost
- Check the cavity width with a borescope survey
- Make sure the installer provides a CIGA guarantee
- Fix gutters and pointing first to avoid damp
- Check eligibility for free cavity insulation under GBIS
Frequently asked questions
How do I know if I have cavity walls?
Brickwork in a stretcher pattern (all long sides) and walls over 260mm thick usually mean a cavity.
Can cavity wall insulation cause damp?
In unsuitable or poorly maintained walls it can. A proper survey and CIGA guarantee protect you.
How long does it take?
Usually two to four hours for a typical house.
Is there a grant?
ECO4 and the Great British Insulation Scheme can fund it for eligible households.
Sources and methodology
Energy prices come from the Ofgem price cap for Direct Debit customers (GB average). Installation costs are typical UK ranges from installer quotes and industry guidance, rounded. Savings use today's rates and do not predict future prices.