What does cavity wall insulation cost in the UK in 2026?
Last updated: April 2026
Cavity wall insulation (CWI) involves filling the gap between the inner and outer leaves of a double-skin wall with insulating material — typically mineral wool beads or EPS (expanded polystyrene) beads injected through small holes in the external brickwork. It is one of the most cost-effective energy efficiency measures for UK homes built after 1920.
Approximately 9 million UK homes still have uninsulated cavity walls. Properly installed CWI reduces heat loss through walls by up to 35%, saving £200–£300 per year on energy bills for a typical semi-detached house.
Costs range from £700 to £2,500 depending on home size. Many homes qualify for free installation through the ECO4 scheme or the Great British Insulation Scheme. Solid wall homes (pre-1920 Victorian and Edwardian terraces) require a different, more expensive approach — internal or external wall insulation.
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This is an estimate based on average 2026 prices. Actual costs may vary. Always request multiple quotes for an exact price.
Cost factors
Cavity wall insulation costs by property type. Many homeowners qualify for free installation through government schemes.
- Mid-terraced house (typical): £700–£1,200
- Semi-detached house (typical): £800–£1,500
- Detached house (typical): £1,200–£2,500
- Removal of failed CWI (if needed): £2,000–£5,000
- Cavity wall survey (before installation): £100–£300
Payback periods for paid-for CWI are typically 3–5 years. With ECO4 or GBIS funding, the investment pays back immediately through energy savings.
Why do prices vary?
- Wall construction type: CWI only works for cavity walls (generally post-1920 construction). Solid-wall Victorian and Edwardian properties need internal or external wall insulation, which costs significantly more.
- Cavity condition: A cavity survey checks for debris, existing partial insulation, and wall ties. Contaminated or narrow cavities may not be suitable for standard CWI.
- Property size and exposure: Larger homes and those in exposed/coastal locations require more material. Severely exposed sites may need specialist materials (e.g., foam rather than beads) to prevent moisture ingress.
- Existing moisture issues: Damp problems must be resolved before installing CWI — insulation can trap moisture and cause internal damp if the external wall has water ingress issues.
- Eligibility for free schemes: ECO4 and GBIS cover many homes free of charge. Always check eligibility before paying.
Subsidies & incentives
Two schemes offer free or subsidised cavity wall insulation:ECO4: Free for households on qualifying benefits. Funded by energy suppliers. Runs to March 2026.Great British Insulation Scheme (GBIS): Open to EPC D–G rated homes in council tax bands A–D. Runs to March 2026.VAT on cavity wall insulation is 0% as an Energy Saving Material. Scotland has additional support through Home Energy Scotland grants and loans.
Regional price differences
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