How much does breathable insulation cost?
Guide prices per layer, realistic whole-project ranges for period homes, and an honest account of what changes the number.
The short answer
Breathable wall insulation starts from around £45/m² for the core insulating layer, supply only, excluding VAT. A complete installed project on a typical Victorian terrace usually lands between £8,000 and £20,000.
That is more than PIR board. It is considerably less than repairing a solid wall that has been insulated with the wrong system for five years.
Material costs, layer by layer
These are the guide prices for each component. They are supply only and exclude VAT, so they are useful for understanding where the money goes rather than as a quotation.
| Layer | Function | Thickness | λ (W/m·K) | Sd (m) | Guide price /m² |
|---|---|---|---|---|---|
| PerliScratch | Lime-perlite scratch / key coat | 3–5 mm | 0.080 | 0.02–0.04 | £4.60 |
| PerliTherm | Expanded perlite insulating render, hydraulic lime bound | 50 mm | 0.064 | 0.2–0.4 | £45.00 |
| AeroBond | Fibre-reinforced lime-polymer adhesive and basecoat | 3–6 mm | 0.12 | 0.02–0.04 | £20.00 |
| Aerogel layer | Silica aerogel blanket for constrained build-ups | 10 mm | 0.017 | 0.04–0.08 | £23.70 |
| PerliFinish | Breathable lime finish coat | 20 mm | — | 0.10–0.20 | £6.60 |
Guide prices are supply only, excluding VAT, and are indicative. Every build-up is specified per project. See the full cost guide.
A standard wall build-up uses PerliScratch, PerliTherm and PerliFinish, which comes to roughly £56/m² in materials. Adding an aerogel layer where depth is constrained — window reveals, for instance — takes it to around £100/m² in those areas only. Most projects use aerogel selectively rather than across whole walls, because it costs five times as much per millimetre of build-up saved.
| Layer | Function | Thickness | λ (W/m·K) | Sd (m) | Guide price /m² |
|---|---|---|---|---|---|
| PerliMat | Vapour-permeable geotextile separator | 3.5 mm | n/a | Vapour open | £3.00 |
| PerliBase | Mineral insulating floor underbase | 75–200 mm | 0.045 | 0.3–0.6 | £59.25 |
| PerliStruct | Lime-perlite structural screed / underbase | 30–150 mm | 0.080–0.090 | 0.20–0.40 | from £46.00 |
| AeroBond | Fibre-reinforced lime-polymer adhesive and basecoat | 5 mm | 0.12 | 0.02–0.04 | £20.00 |
| Aerogel layer | Silica aerogel blanket | 5 mm | 0.017 | 0.04–0.08 | £23.25 |
| PerliScreed | Vapour-open, membrane-free floor screed | 75–200 mm | 0.045 | 0.3–0.6 | £59.25 |
Guide prices are supply only, excluding VAT, and are indicative. Every build-up is specified per project. See the full cost guide.
Realistic whole-project costs
Materials are typically 40–55% of an installed project. The rest is preparation, labour, access, making good and decoration. These ranges are installed costs including labour.
| Scope | Typical installed range | Notes |
|---|---|---|
| Single room, one external wall | £1,500 – £3,500 | The usual starting point. Often a bedroom with a persistent cold or damp wall. |
| Single room, fully treated | £3,000 – £6,000 | All external walls plus reveals and junction detailing. |
| Victorian or Georgian terrace, whole house | £8,000 – £20,000 | Walls only. The spread reflects room count, wall condition and access. |
| Whole house including floors | £15,000 – £35,000 | Floor build-ups require excavation and a longer programme. |
| Listed building, whole house | Assessed individually | Consent, bespoke detailing and phased working change the arithmetic. |
What pushes the cost up or down
Wall condition
Sound lime-plastered walls need little preparation. Walls with failed cement render, blown plaster or defective pointing need remedial work first, and that can add 20–30%.
Existing damp
Rising damp, leaking rainwater goods or a raised external ground level must be resolved before insulating. Insulating over an unresolved moisture source guarantees failure.
Depth available
Where a deep build-up is acceptable, perlite alone does the job cheaply. Where reveals and room proportions constrain you to 25–30 mm, aerogel is required and costs rise.
Doing it in one go
Room-by-room over several years costs more in total than a single programme, because mobilisation, access and making good are repeated each time.
Occupied or empty
Working around furniture and residents is slower. An empty property during a wider renovation is the cheapest time to do this work.
Floors as well as walls
Floors are a bigger job than walls — excavation, a structural underbase and a screed — but they are also where a large share of the heat loss usually sits.
VAT: a deadline worth knowing about
Installation of qualifying energy-saving materials in residential property is currently zero-rated for VAT until 31 March 2027. From 1 April 2027 it is due to revert to the reduced rate of 5%.
The relief applies where a contractor supplies and installs the materials. Buying materials on their own does not qualify. On a £15,000 project the difference between 0% and 5% is around £750 — not decisive on its own, but real.
Source: HMRC VAT Notice 708/6. Rules change; confirm the position with your installer or accountant before relying on it.
The cost of getting it wrong
The reason breathable systems look expensive is that they are usually compared against the cheapest possible alternative rather than against the alternative's full lifetime cost.
PIR board fixed to a solid wall is cheaper on day one. If it causes interstitial condensation, the costs that follow are: stripping out the failed insulation, drying the wall, replacing decayed joist ends and embedded timbers, re-plastering, redecorating, and then doing the original job again properly. Wet masonry also conducts heat up to three times faster than dry masonry, so the thermal performance you paid for degrades while the damage accumulates.
None of that shows up in a quotation. It shows up at the next survey, which is also where it affects what the property is worth.
Reducing what you pay
- Check grant eligibility first. The Warm Homes: Local Grant can fund up to £15,000 of energy efficiency work for eligible households. See which schemes are still open.
- Prioritise the worst walls. North-facing and exposed elevations give the largest return per pound spent.
- Combine it with work you are already doing. If a room is being stripped anyway, the marginal cost of insulating it drops sharply.
- Fix the cheap things first. Draught-proofing, loft insulation and functioning rainwater goods cost little and change what the wall has to cope with.
A free property assessment produces an indicative cost breakdown specific to your building, with no obligation.
Book a free property assessment
A specialist visits your property, assesses the wall construction, and produces a written build-up recommendation with indicative costs. No obligation, no hard sell.