Loft, cavity wall, external wall, underfloor and foil insulation costs compared for UK homes. Updated August 2026, based on current installer data.
Indicative estimate for every measure your home may need — not a quotation.
Key fact: A significant amount of heat — often around a quarter — can escape through the roof if your insulation isn’t up to modern standards. Heat naturally rises, so without effective insulation in place, it escapes through your roof — increasing energy bills and reducing comfort in your home.
Every type scored across cost, efficiency, lifespan, risk, and installation complexity
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Check My Home in 30 Seconds →| Insulation type | Typical scope | Cost range | Annual saving | Payback |
|---|---|---|---|---|
| Loft insulation (0→270mm) | Semi-detached | £600–£900 | £150–£350 | 2–6 years |
| Loft insulation (top-up) | Semi-detached | £750–£900 (EST, May 2026) | £80–£200 | 2–4 years |
| Cavity wall insulation | Semi-detached | £1,600–£2,800 | £100–£300 | 5–15 years |
| External wall insulation | Solid wall / semi | £8,000–£20,000 | £300–£700 | 15–30 years |
| Internal wall insulation | Solid wall / semi | £5,000–£12,000 | £200–£500 | 10–25 years |
| Underfloor (suspended) | Ground floor only | £1,400–£2,500 | £50–£150 | 10–30 years |
| Underfloor (solid) | Ground floor only | £4,000–£8,000 | £50–£150 | 25+ years |
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Cost ranges are indicative for August 2026 based on Energy Saving Trust benchmarks and UK installer data. Actual costs depend on property type, size, access, existing insulation and installer. Savings assume average UK energy prices (Ofgem Q3 2026 price cap). ECO4 may fully fund some measures for eligible households.
Spray foam warning: Multiple major UK mortgage lenders decline applications on homes with spray foam on roof timbers. See our full spray foam risks guide.
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Check My Home Now →Cost data: Energy Saving Trust benchmarks (August 2026) and UK installer quotes. Grants: GOV.UK and official scheme operators. Savings: Ofgem Q3 2026 price cap £1,862/year. All figures indicative. Last reviewed: August 2026. View scoring methodology →
Cost data: Energy Saving Trust benchmarks (August 2026) and UK installer quotes. Grants: GOV.UK and official scheme operators. Savings: Ofgem Q3 2026 price cap £1,862/year. All figures indicative. Last reviewed: August 2026. View scoring methodology →