Most insulation “cost guides” are estimates aggregated from other estimates. This one is different: it is built from 454 real quotes our own team priced across London and the South-East, including 35 jobs we won and installed — published individually below, anonymised to the month, postcode district and price. No modelling, no national averages — what London homeowners were actually quoted, and what the ones who went ahead actually paid.
Key findings
- External wall insulation: median completed project £19,180 (12 jobs). Real all-in cost of measured jobs: £176–£232 per m² of treated wall — noticeably above the £110–£140/m² headline system rate everyone (including us) advertises, because scaffolding and detailing are part of every real project.
- Internal wall insulation: median project £3,900 (13 jobs, from £1,840 for a couple of rooms to £9,950 for larger houses). Finished jobs with measured areas: £213–£216/m².
- Loft & roof: median £2,680 (9 jobs). Straightforward top-ups clustered around £2,300–£2,700; rafter and flat-roof systems ran £1,900–£11,600 depending on size and build-up.
- Floor insulation: 59 priced projects, median £4,320; suspended timber floors typically quoted at £76–£110/m².
- Prices vary less by postcode than by property. The same measure in Ruislip, Kingston or South Norwood priced within a narrow band — wall area, access and detailing drove cost, not the borough.
Where the data comes from
Every row in this report is a quote our team prepared, the customer accepted, and we installed — pulled from our quoting system and anonymised before publication (month, area district, m² and price only; never an address). We are a PAS2030-19 and TrustMark certified installer (licence 2259022) rated 9.87/10 on Checkatrade across 122 verified reviews. Figures are totals paid for privately-funded work, including scaffolding and making good where the job needed it.
Two datasets feed this report. First, the whole quote book: 454 priced quotes, used only as aggregates (medians and quartile ranges). Second, the installed record: the 35 jobs customers accepted and we completed, published individually. One honest caveat: this is one installer's book, not a national survey. Treat the medians as what a well-run London installer actually charges, not as the cheapest price the internet can find you.
The whole quote book — 454 priced quotes
Quoted whole-project prices by measure. The typical range is the middle half of all quotes (25th–75th percentile) — half of everything we price lands inside it.
| Measure | Quotes | Median project | Typical range | Measure rate |
|---|---|---|---|---|
| External wall (EWI) | 170 | £17,300 | £11,880 – £23,118 | £130–£140/m² |
| Internal wall (IWI) | 108 | £5,550 | £3,828 – £9,701 | £130–£140/m² |
| Loft & roof | 117 | £3,825 | £2,830 – £5,854 | £40–£40/m² |
| Floor | 59 | £4,320 | £2,927 – £6,705 | £76–£110/m² |
The measure rate is the per-m² price of the insulation work itself, as quoted on surveyed jobs — scaffolding, access and making good sit on top, which is why finished whole-job costs per m² run higher (see the EWI section below).
External wall insulation — 12 real jobs
Median completed project: £19,180. Range: £3,800 (partial elevation) to £32,220 (large detached). Jobs with measured wall areas came out between £176 and £232 per m² all-in. Full breakdown of what EWI includes is in our EWI service guide.
| When | Area | Measure | Size | Price | £/m² |
|---|---|---|---|---|---|
| April 2026 | Worcester Park (KT4) | External wall insulation | 58 m² | £13,352 | £232 |
| March 2026 | South Norwood (SE25) | External wall insulation | 62 m² | £12,600 | £202 |
| January 2026 | Ruislip (HA4) | External wall insulation | 102 m² | £17,898 | £176 |
| October 2025 | Kingston upon Thames (KT2) | External wall insulation | 90 m² | £19,520 | £216 |
Internal wall insulation — 13 real jobs
IWI is the phased measure: most customers insulate a few rooms at a time, which is why the median project (£3,900) is far below a whole-house figure. See the IWI service guide for systems and room-loss detail.
| When | Area | Measure | Size | Price | £/m² |
|---|---|---|---|---|---|
| June 2026 | East Dulwich (SE22) | Internal wall insulation | 13 m² | £2,700 | £216 |
| April 2026 | Crystal Palace (SE19) | Internal wall insulation | 14 m² | £2,980 | £213 |
| May 2025 | Watford (WD19) | Internal wall insulation | — | £5,120 | — |
| April 2025 | Shepherd's Bush (W12) | Internal wall insulation | — | £5,300 | — |
| January 2025 | Kilburn (NW6) | Internal wall insulation | — | £3,540 | — |
| January 2025 | Potters Bar (EN6) | Internal wall insulation | — | £5,420 | — |
| January 2025 | Carshalton (SM5) | Internal wall insulation | — | £3,070 | — |
| November 2024 | Leyton (E10) | Internal wall insulation | — | £3,900 | — |
Loft & roof — 9 real jobs
“Loft insulation” hides three very different jobs: cheap cold-loft top-ups, rafter-line systems for rooms-in-roof, and flat-roof build-ups. The table shows why the range is wide. More in the loft & roof service guide.
| When | Area | Measure | Size | Price | £/m² |
|---|---|---|---|---|---|
| June 2026 | Crystal Palace (SE19) | Flat roof insulation | 17 m² | £6,735 | £396 |
| June 2026 | Richmond (TW10) | Roof rafter insulation | — | £1,894 | — |
| June 2026 | East Dulwich (SE22) | Loft insulation top-up | 42 m² | £2,340 | £56 |
| April 2026 | Highgate (N6) | Roof rafter insulation | 105 m² | £11,576 | £110 |
| March 2026 | Finsbury Park (N4) | Loft insulation top-up | 35 m² | £2,600 | £74 |
| February 2026 | Wimbledon (SW19) | Loft insulation top-up | 40 m² | £2,448 | £61 |
| January 2026 | Greenford (UB6) | Loft insulation top-up | 35 m² | £4,580 | £131 |
| November 2025 | Kingston upon Thames (KT2) | Flat roof insulation | 15 m² | £7,242 | £498 |
| January 2025 | South Norwood (SE25) | Loft insulation top-up | — | £2,680 | — |
Floor insulation — 59 priced projects
Floor-only installs are rarer in the won record (1 standalone job — floor work usually rides along with wall or loft projects), but the quote book is deep: 59 floor projects priced, median £4,320, with suspended timber floor rates typically £76–£110 per m². See the floor insulation guide for what drives it.
Every job in the dataset
| When | Area | Measure | Size | Price | £/m² |
|---|---|---|---|---|---|
| June 2026 | Crystal Palace (SE19) | Flat roof insulation | 17 m² | £6,735 | £396 |
| June 2026 | Richmond (TW10) | Roof rafter insulation | — | £1,894 | — |
| June 2026 | East Dulwich (SE22) | Internal wall insulation | 13 m² | £2,700 | £216 |
| June 2026 | East Dulwich (SE22) | Loft insulation top-up | 42 m² | £2,340 | £56 |
| April 2026 | Crystal Palace (SE19) | Internal wall insulation | 14 m² | £2,980 | £213 |
| April 2026 | Worcester Park (KT4) | External wall insulation | 58 m² | £13,352 | £232 |
| April 2026 | Highgate (N6) | Roof rafter insulation | 105 m² | £11,576 | £110 |
| March 2026 | Finsbury Park (N4) | Loft insulation top-up | 35 m² | £2,600 | £74 |
| March 2026 | South Norwood (SE25) | External wall insulation | 62 m² | £12,600 | £202 |
| February 2026 | Wimbledon (SW19) | Loft insulation top-up | 40 m² | £2,448 | £61 |
| January 2026 | Ruislip (HA4) | External wall insulation | 102 m² | £17,898 | £176 |
| January 2026 | Greenford (UB6) | Loft insulation top-up | 35 m² | £4,580 | £131 |
| November 2025 | Kingston upon Thames (KT2) | Flat roof insulation | 15 m² | £7,242 | £498 |
| October 2025 | Kingston upon Thames (KT2) | External wall insulation | 90 m² | £19,520 | £216 |
| June 2025 | High Wycombe (HP11) | External wall insulation | — | £23,350 | — |
| May 2025 | Watford (WD19) | Internal wall insulation | — | £5,120 | — |
| April 2025 | Shepherd's Bush (W12) | Internal wall insulation | — | £5,300 | — |
| April 2025 | Raynes Park (SW20) | External wall insulation | — | £22,130 | — |
| January 2025 | South Norwood (SE25) | Loft insulation top-up | — | £2,680 | — |
| January 2025 | Worcester Park (KT4) | External wall insulation | — | £19,180 | — |
| January 2025 | Tooting (SW17) | External wall insulation | — | £3,800 | — |
| January 2025 | Kilburn (NW6) | Internal wall insulation | — | £3,540 | — |
| January 2025 | Potters Bar (EN6) | Internal wall insulation | — | £5,420 | — |
| January 2025 | Carshalton (SM5) | Internal wall insulation | — | £3,070 | — |
| January 2025 | Southall (UB1) | External wall insulation | — | £16,590 | — |
| November 2024 | East Horsley (KT24) | External wall insulation | — | £32,220 | — |
| November 2024 | Leyton (E10) | Internal wall insulation | — | £3,900 | — |
| November 2024 | Woking (GU21) | External wall insulation | — | £19,180 | — |
| November 2024 | Ruislip (HA4) | External wall insulation | — | £30,580 | — |
| October 2024 | Carshalton (SM5) | Internal wall insulation | — | £3,850 | — |
| October 2024 | Chingford (E4) | Internal wall insulation | — | £1,840 | — |
| June 2024 | Teddington (TW11) | Internal wall insulation | — | £9,950 | — |
| March 2024 | Chesham (HP5) | Internal wall insulation | — | £5,400 | — |
| February 2024 | Camberwell (SE5) | Suspended floor insulation | — | £1,250 | — |
| January 2024 | Hounslow (TW4) | Internal wall insulation | — | £7,470 | — |
Dataset last regenerated August 2026. Districts shown are outward postcodes only — never full addresses.
What actually moved the price
- Treated area — the dominant factor; fixed costs dilute on bigger jobs.
- Scaffolding and access — every EWI job carries it; tight terraces cost more per m².
- Detailing density — windows, reveals, sills and eaves take time; a plain gable is cheap per m².
- System choice — breathable wood-fibre IWI runs 15–25% over rigid board; render choice moves EWI.
- Making good — IWI includes skimming, sockets, skirtings; it is a finishing trade as much as an insulation one.
Want your own number instead of a median? Get a free, fixed, itemised quote — surveyed first, priced within 24 hours.
FAQ
How much does external wall insulation really cost in London in 2026?
Across the 12 EWI jobs we won and installed in this dataset, the median project came to £19,180, with whole projects ranging from £3,800 (a partial, single-elevation job) to £32,220 (a large detached house). Measured per square metre of treated wall, completed jobs worked out at £176–£232/m² all-in.
Why is the real per-m² cost higher than the advertised rate?
Advertised EWI rates (ours included, at £110–£140/m²) describe the insulation system itself — board, render and labour. A finished project also carries scaffolding, beading, reveal and sill detailing, and making good. Spread those over the treated area and real completed jobs land at £176–£232 per m². Any installer quoting only a headline rate will surprise you later; a fixed itemised quote will not.
How much does internal wall insulation cost in London?
The median IWI project in this dataset was £3,900 — most jobs treat a few rooms rather than a whole house. Projects ranged from £1,840 to £9,950, and the two jobs with measured wall areas both came out at £213–£216/m² fully finished.
How much does suspended floor insulation cost?
Across 59 floor projects we priced, the median came to £4,320, with suspended timber floor rates typically £76–£110 per m² depending on access — insulating from below via a cellar or crawl space is cheaper than lifting and refitting boards.
Is this data real? Can I verify it?
Yes — every row is a genuinely won, installed job from our quoting system, anonymised to the month, area district and price. We publish it because no price-comparison site can: they aggregate estimates, we install. Cross-check us against our 9.87/10 Checkatrade rating from 122 verified reviews.