Insulation costs are quoted in a confusing mix of per-square-metre rates, per-room prices and whole-house figures — which makes it hard to know what's fair before anyone visits. This guide lays out real 2026 prices for London and the South-East, broken down by measure and by property size, so you can budget with confidence. All figures are for privately-funded work, fully installed.
Insulation cost at a glance
| Measure | Typical price | Per m² | Payback |
|---|---|---|---|
| Loft top-up | £400 – £900 | — | 2–4 years |
| Floor (3-bed) | £1,800 – £4,500 | £20–£100 | 5–10 years |
| Internal wall (house) | £8,000 – £15,000 | £50–£90 | 8–15 years |
| External wall (3-bed semi) | £12,000 – £20,000 | £90–£140 | 10–20 years |
The headline: loft and floor insulation are the quick, low-cost wins; wall insulation is a bigger investment that delivers the biggest comfort and bill improvement on solid-wall homes. Most households start with the roof and floor and treat walls when budget allows.
Loft & roof insulation cost
| Job type | Indicative cost | Notes |
|---|---|---|
| Cold-loft top-up (to 270mm) | £400 – £900 | Cheapest, fastest payback |
| Full re-insulation of a 3-bed loft | £700 – £1,500 | Includes removing old material |
| Room-in-roof / rafter system | £3,000 – £7,500 | Keeps a converted loft usable |
| Warm flat-roof build-up | £90 – £150 / m² | Best done at re-cover stage |
Floor insulation cost
| Job type | Indicative cost | Notes |
|---|---|---|
| Suspended timber (from below) | £20 – £40 / m² | Easiest with cellar/crawl space |
| Suspended timber (lifting boards) | £40 – £70 / m² | More labour to lift & refit |
| Solid floor (rigid board over slab) | £60 – £100 / m² | Usually part of a renovation |
| Typical 3-bed ground floor | £1,800 – £4,500 | Whole ground floor |
Internal wall (IWI) insulation cost
| Job type | Indicative cost | Notes |
|---|---|---|
| Single room | £1,500 – £3,500 | Good way to phase the cost |
| Full 3-bed house | £8,000 – £15,000 | All external walls treated |
| Per m² (board + finish + labour) | £50 – £90 / m² | Rigid insulated plasterboard |
| Breathable wood-fibre system | +15–25% | Premium for heritage build-ups |
External wall (EWI) insulation cost
| Job type | Indicative cost | Notes |
|---|---|---|
| Mid-terrace (rear/side elevations) | £8,000 – £14,000 | Fewer elevations to treat |
| Typical 3-bed semi-detached | £12,000 – £20,000 | Most common project size |
| Detached house | £18,000 – £30,000+ | Depends on footprint |
| Per m² (system + render + labour) | £90 – £140 / m² | Useful for rough estimates |
What changes the price
The same measure can vary widely between two homes. The biggest factors:
- Property size and number of elevations — the single largest driver for wall insulation.
- Access — a cellar or crawl space makes floor insulation far cheaper than lifting every board; scaffolding adds cost to EWI.
- System chosen — premium phenolic or breathable wood-fibre boards cost more than standard EPS or mineral wool.
- Finish and making good — render colour and texture, plus reinstating skirtings, sockets and decoration.
- Detailing — bay windows, complex rooflines and tricky junctions all add labour.
- Condition — damp, failed render or rotten joists must be put right first.
This is exactly why a free survey matters: a fixed, itemised quote based on your actual property beats any online estimate. See the full detail on each measure in our loft, floor, internal wall and external wall guides, or compare the two wall options in our EWI vs IWI guide.
Insulation cost FAQs
How much does insulation cost in the UK in 2026?
It depends entirely on the measure. As a guide for London and the South-East: a loft top-up is £400–£900, floor insulation £1,800–£4,500 for a typical ground floor, internal wall insulation £8,000–£15,000 for a full house (£50–£90/m²), and external wall insulation £12,000–£20,000 for a 3-bed semi (£90–£140/m²).
What is the cheapest insulation measure?
A cold-loft top-up is the cheapest and has the fastest payback — typically £400–£900 and paying for itself in 2–4 years, because around a quarter of a home’s heat escapes through the roof.
Why is external wall insulation so expensive?
EWI is a whole-house external system: it includes scaffolding, insulation boards, a multi-coat render finish and detailing around every window, door and eave. That labour and material make it the most expensive measure — but also the most thermally effective for solid-wall homes.
Is insulation cheaper per m² on a bigger job?
Usually a little, yes. Fixed costs like scaffolding, set-up and surveying are spread over more area, so the per-m² rate tends to fall on larger jobs. That’s why whole-house projects often represent better value per square metre than treating a single elevation.
Does a quote include VAT and making good?
Our quotes are fixed and itemised, and we tell you exactly what’s included — materials, labour, scaffolding where needed, and making good. Some energy-saving measures qualify for 0% VAT under current rules; we confirm the VAT position in writing on your quote.