Estimate your range
Typical floor areas are assumed for each property type. Your quote will use measured areas.
Indicative installed costs by route
| Route | Typical semi-detached | Per m² | What moves the price |
|---|---|---|---|
| Loft floor, mineral wool to 270mm | £450 – £1,600 | £10 – £22 | Access, existing depth, pipes and tanks, clearing old material |
| Loft insulation with raised boarding | £800 – £2,200 | £25 – £45 boarded area | Boarded area, joist height, loft hatch and ladder |
| Multifoil to rafters | £2,000 – £6,500 | £45 – £80 | Roof area, access, whether PIR is combined, plasterboard finish |
| Room-in-roof insulation | £2,500 – £7,000 | £55 – £110 | Sloping ceilings, dwarf walls, whether the room is stripped back |
| Cavity wall fill | £700 – £2,500 | £8 – £16 | Wall area, cavity width, scaffold, extraction of old fill |
| Internal wall insulation | £4,000 – £12,000 | £60 – £120 | Number of external walls, replastering, moving services |
| External wall insulation | £8,000 – £20,000 | £90 – £160 | Scaffold, render finish, detailing at windows and eaves |
| Underfloor (suspended timber) | £800 – £2,800 | £18 – £40 | Void access, whether boards are lifted, material choice |
| Spray foam removal only | £2,000 – £6,000 | £25 – £50 | Foam type, roof area, membrane condition, disposal |
How these numbers were reachedRanges compiled from published UK cost guides and installer input, compiled and reviewed 3 September 2026. We will replace them with anonymised quote data from this site as it accumulates. Read how we estimate.
The five variables that matter most
- Area. Everything is priced per square metre. A detached house has roughly twice the loft floor of a mid-terrace.
- Access. No hatch, a small hatch, a water tank in the way or a loft full of belongings all add labour.
- What is there now. Old insulation, spray foam or damaged boarding may need removing first.
- Finish. A multifoil left exposed in a loft is cheap. Plasterboarded and skimmed in a loft room is not.
- Scaffold. Anything external — EWI, cavity fill on upper floors, some roof work — carries scaffold cost.
Want a number for your home, not a table?
Check my homeTell us the property and the problem. We show a range, then you decide whether to get quotes.
Cheapest first: where the money goes furthest
For most UK homes the order of payback is loft floor, then cavity walls, then draughtproofing and floors, then roof slope and solid walls. A loft top-up is often the only measure that pays for itself within a few years at current energy prices. If the loft is already at 270mm, the next best return is usually walls, not more loft.
Cost guides by route
Questions homeowners ask
Why are your ranges so wide?
Because honest ones are. A loft top-up in a bungalow with a good hatch and a clear floor is a morning's work; the same job with a tank, old insulation and boxes to move is two days. We would rather show a wide band than a precise wrong number.
Do the prices include VAT?
Energy-saving materials installed in residential property have been zero-rated for VAT in Great Britain since 2022, so most quotes will show no VAT on the installation. Confirm this on the quote.
Is it cheaper to do it myself?
Loft floor insulation, yes — materials for a typical semi are a few hundred pounds. Roof slope, cavity walls and wall systems are not sensible DIY projects because the moisture detailing is where it goes wrong.
Sources and when they were last checked
- Checkatrade — Loft insulation cost guide — checked 2 September 2026
- MyBuilder — Loft insulation cost guide — checked 2 September 2026
- Energy Saving Trust — Roof and loft insulation — checked 2 September 2026