Installed costs for every major insulation measure — one citable dataset, methodology stated, updated as benchmarks move. Current edition: Q3 2026 (verified 28 August 2026).
| Measure | Typical £/m² | Whole-property (typical) | Complexity | Funding routes |
|---|---|---|---|---|
| Loft (270mm from bare) | £18–£28/m² | £900 typical semi | Low | ECO4 / WH:LG |
| Loft top-up (120→270mm) | £15–£22/m² | £750 typical semi | Low | ECO4 / WH:LG |
| Cavity wall | £14–£22/m² | £2,700 typical semi | Low–Med | ECO4 / WH:LG / GBIS-era stock |
| External wall (EWI) | £95–£135/m² | £18,000 typical 3-bed semi | High | ECO4 / WH:LG |
| Internal wall (IWI) | £60–£95/m² | £12,000 typical 3-bed semi | High | ECO4 / WH:LG |
| Underfloor (suspended) | £25–£50/m² | £1,000–£2,600 | Med | ECO4 / WH:LG |
| Room-in-roof | £55–£90/m² | £3,000–£7,500 | Med–High | ECO4 / WH:LG |
| Flat roof (warm-deck) | £80–£120/m² | £2,500–£5,000 | Med | With re-covering |
| Pitched roof (rafter PIR) | £45–£75/m² | £2,000–£5,500 | Med | Renovation-led |
| Fibreglass/mineral wool quilt (supply) | £4–£8/m² | materials only | DIY-possible | — |
| PIR board (supply) | £8–£14/m² | materials only | DIY-possible | — |
| Blown cavity refill (post-extraction) | £18–£30/m² | £3,000–£4,500 | Med | Case-by-case |
| Spray foam removal | £25–£45/m² | £1,500–£4,000+ | High | Not funded |
Sources: Energy Saving Trust cost benchmarks (May 2026) as the anchor, cross-referenced against public installer pricing and scheme-reported costs. VAT: all installed prices assume the 0% rate on energy-saving materials (to 31 March 2027). Labour: included in installed figures; supply-only rows are materials at retail. Property basis: \u201cTypical semi\u201d = 3-bed, ~90m². Regional variation: London/South East typically +10–20%; we do not publish per-region precision we cannot source. No fake precision: ranges are honest ranges.
Journalists, councils and researchers are welcome to cite this page as \u201cInsulation Comparisons UK Insulation Price Index, Q3 2026\u201d with a link. The index is updated when EST benchmarks move, when VAT treatment changes, and at each quarterly review — next scheduled review: November 2026 (alongside the WH:LG statistical release on 26 November).
Most measures above are fundable for eligible households via ECO4 (to 31 Dec 2026) or the Warm Homes: Local Grant (to Mar 2028) — could be fully funded for some eligible households; eligibility does not guarantee installation or zero customer contribution. The 60-second check maps your home to its routes before you spend a pound.
AC-coupled (battery has its own inverter) is the retrofit default: no rewiring of your array, works with any brand or age of system, £3,500–£6,000 installed for 5–10kWh usable. DC-coupled only makes sense if your inverter is due replacement anyway — a hybrid inverter + battery swap can be cheaper combined.
Feed-in Tariff payments are unaffected by adding storage — generation payments continue and deemed export isn’t metered down. On SEG, a battery lets you shift export into peak-price windows instead.
Match usable capacity to your evening consumption and summer surplus — the sizing guide has the tables. Most 4kWp homes land at 5–8kWh usable.
Loft quilt £18–£28/m², cavity wall £14–£22/m², EWI £95–£135/m², IWI £60–£95/m², suspended floor £25–£50/m² — all installed, 0% VAT, EST-anchored (May 2026).
Quarterly, and whenever Energy Saving Trust benchmarks or VAT treatment change. Current edition: Q3 2026; next review November 2026.
No — indicative national ranges with stated assumptions. Real quotes depend on survey, access, condition and region (London/SE typically +10–20%).
Yes — cite 'Insulation Comparisons UK Insulation Price Index, Q3 2026' with a link to this page.
Facts checked 21 August 2026. We link to official sources and show when facts were last verified. If a scheme changes, we update the page.
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