Typical 2026 UK costs by house type and per m², internal vs external, the savings and grants.
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If your home was built before about 1920 it probably has solid walls, which lose more heat than cavity walls and cannot be filled in the same way. Solid wall insulation is fitted to the inside or outside of the wall. External wall insulation is the more common choice, and costs from around £6,000 for a mid-terrace up to £20,000 to £30,000 for a detached house. Here is the full breakdown.
These are typical external wall insulation costs, the most common approach for solid-walled homes.
| House type | Typical cost (external, installed) |
|---|---|
| Detached house | £20,000 to £30,000 |
| Semi-detached house | £14,000 to £20,000 |
| Mid-terrace house | £6,000 to £10,000 |
| Detached bungalow | £15,000 to £21,000 |
| Mid-floor flat | £5,000 to £7,000 |
| Material | Typical cost per m² (installed, incl render) |
|---|---|
| Expanded polystyrene (EPS) | £145 to £195 |
| Mineral wool | £155 to £205 |
| Foil-faced boards | £150 to £200 |
| Phenolic foam | £150 to £200 |
Cost figures: Checkatrade (2026); savings from the Energy Saving Trust. Verified August 2026. Typical estimates only, your quote will vary.
External wall insulation fixes boards to the outside and renders over them, so it does not reduce room sizes and it weatherproofs the wall, but it costs more and changes how the home looks. Internal wall insulation is cheaper but reduces each room by around four inches and is more disruptive to fit. Which suits you depends on your budget, whether the exterior can be altered, and how much internal space you can spare.
Around a third of the heat in an uninsulated home escapes through the walls, and the Energy Saving Trust suggests solid wall insulation could save up to around £330 a year. Because the upfront cost is high, the payback period is long, roughly 15 to 25 years, so grant funding makes a real difference to whether it stacks up.
For a genuinely cold, solid-walled home it can transform comfort and cut a big share of heat loss, and it lifts your EPC rating. It is a large investment with a long payback though, so it is most worthwhile if you plan to stay in the home or can access a grant. Comparing quotes and checking eligibility first is essential.
The ECO4 scheme can substantially reduce the cost for eligible households, and the Warm Homes: Local Grant may help low-income homes in England. Check our 2026 insulation grants guide, and always get several quotes from vetted, certified installers. See also our cavity wall insulation cost guide if you are not sure which walls you have.
Solid (external) wall insulation typically costs from around £6,000 for a mid-terrace up to £20,000 to £30,000 for a detached house, based on Checkatrade 2026 figures. Priced by wall area it works out at roughly £150 to £200 per m² installed, including render.
The total installed cost, including insulation boards, fixings and render, runs from about £150 to £200 per m², averaging £175. EPS is at the lower end (£145 to £195), mineral wool a little higher (£155 to £205).
Around a third of an uninsulated home's heat escapes through the walls, and the Energy Saving Trust suggests solid wall insulation could save up to around £330 a year. Because the upfront cost is high, the payback period is long, roughly 15 to 25 years, which is why grants make a real difference.
For a cold, solid-walled home it can transform comfort and cut a large share of heat loss, and it improves your EPC rating. But it is a big investment with a long payback, so it is most worthwhile if you plan to stay put or can access grant funding.
External insulation fixes boards to the outside of your walls and renders over them, so it does not reduce room sizes and weatherproofs the wall, but it is more expensive and changes the look of the home. Internal insulation is cheaper but reduces each room by around four inches and can be disruptive.
Possibly. The ECO4 scheme can substantially reduce the cost for eligible households, and the Warm Homes: Local Grant may help low-income homes in England. Eligibility depends on income, EPC rating and location. See our 2026 insulation grants guide.
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Insulation Advice Centre