How much does external wall insulation cost? Around £15,000 for a typical three-bedroom semi-detached house, according to the Energy Saving Trust (June 2026). Checkatrade's July 2026 price guide puts it at £6,000–£10,000 for a mid-terrace, £14,000–£20,000 for a semi and £20,000–£30,000 for a detached house, or about £175 per m² fitted. Internal wall insulation is cheaper: around £12,000 for the same semi. Fitted insulation carries 0% VAT until 31 March 2027, and low-income households can get it fully funded through an external wall insulation grant. Check if you qualify →Last checked: 30 October 2026
(Energy Saving Trust)
(Energy Saving Trust)
(Checkatrade, July 2026)
External wall insulation cost by house type
The size of your house sets most of the price, because you pay per square metre of wall. A mid-terrace has two exposed walls; a detached house has four, plus more corners, windows and downpipes to work around.
| House type | Low | High | Average |
|---|---|---|---|
| Mid-floor flat | £5,000 | £7,000 | £6,000 |
| Mid-terrace house | £6,000 | £10,000 | £8,000 |
| Semi-detached house | £14,000 | £20,000 | £17,000 |
| Detached bungalow | £15,000 | £21,000 | £18,000 |
| Detached house | £20,000 | £30,000 | £25,000 |
Source: Checkatrade, External wall insulation cost, last updated July 2026 (ballpark averages from its estimators; secondary source). For comparison, the Energy Saving Trust gives around £15,000 for a typical three-bed semi in Great Britain (page updated 18 June 2026).
Expect your quotes to land somewhere between the two sources. MyBuilder's guide (updated 21 August 2026) quotes a lower headline of £6,000–£12,000; its figures look like smaller homes and simpler jobs. Flats are a special case: insulating the outside of one flat usually needs the building owner and neighbours to agree, and flats do not have householder permitted development rights (see planning below).
External wall insulation cost per m²
Installers price EWI per square metre of wall, including boards, fixings, mesh, render or cladding and labour. Scaffolding and the fiddly work around the house are often on top.
| System or material | Installed cost per m² | Source |
|---|---|---|
| Average EWI, all systems | £150–£200 (average £175) | Checkatrade, Jul 2026 |
| EPS (expanded polystyrene) boards | £145–£195 | Checkatrade, Jul 2026 |
| Mineral wool boards | £155–£205 | Checkatrade, Jul 2026 |
| Phenolic foam boards | £150–£200 | Checkatrade, Jul 2026 |
| Foil-faced boards | £150–£200 | Checkatrade, Jul 2026 |
| Basic / mid-range / premium system | £90–£110 / £110–£140 / £140–£180+ | MyBuilder, Aug 2026 |
| Removing old EWI | £30–£40 (average £35) | Checkatrade, Jul 2026 |
Both are trade-directory price guides (secondary sources). Use them to sanity-check quotes, not to replace one.
Quick way to estimate yours: measure the outside walls you want to cover (length × height, minus big windows and doors), then multiply by £150–£200. A semi with 90 m² of exposed wall comes out at roughly £13,500–£18,000 on the Checkatrade rates, which lines up with its £14,000–£20,000 range for a semi.
What pushes the price up (or down)
Two houses with the same wall area can get very different quotes. The Energy Saving Trust says external wall insulation often needs extra work, such as extending the roof and moving rainwater pipes and meter boxes. The usual extras:
- Extending the roof line. The walls get thicker, so eaves and verges often have to be extended to keep rain off the top of the insulation.
- Moving things on the wall. Rainwater downpipes, gas and electricity meter boxes, satellite dishes, outside lights and taps all have to come off and go back on further out.
- Window and door reveals and sills. Insulation has to wrap into the reveals, and sills usually need extending.
- Repairs first. Damaged brickwork or pointing, roofs, overhangs, gutters and downpipes must be fixed before any wall insulation goes on, or you risk trapping damp. That is your cost, not the installer's.
- The finish. A plain through-coloured render sits at the cheap end. Brick slips, tiles or panels cost more.
- Access and scaffolding. Tight side passages, conservatories and three-storey elevations all add time.
The biggest saving: do it when the scaffolding is already up. The Energy Saving Trust says EWI costs less when it is fitted alongside a new roof, new windows, solar panels or gutter repairs, because you only pay for scaffolding once.
Internal wall insulation cost
Internal wall insulation (IWI) puts the insulation on the inside face of your outside walls, so it is the usual choice when you cannot change the outside of the house, such as on a street-facing brick terrace or in a conservation area.
| Internal wall insulation | Typical cost | Source |
|---|---|---|
| Typical 3-bed semi, whole house, redecorated | Around £12,000 | Energy Saving Trust, Jun 2026 |
| Semi-detached house, retrofit | £8,000–£10,000 | Checkatrade, Oct 2026 |
| External wall insulation, same semi (for comparison) | £10,000–£12,500 | Checkatrade, Oct 2026 |
Checkatrade, Retrofit insulation cost, last updated October 2026 (secondary). The Energy Saving Trust figure assumes a company does the whole house in one go and fully redecorates afterwards.
There are three ways to do it, according to the Energy Saving Trust: rigid insulation boards fixed to the wall, a stud wall built in front of the wall and filled with insulation, or insulating plaster. Each one makes the room slightly smaller, and skirting boards, door frames, sockets and radiators have to come off and go back on.
The big plus of internal insulation for solid walls is that you can do it one room at a time, for example when you are redecorating anyway. That is how the Energy Saving Trust suggests keeping the cost down.
External vs internal wall insulation: cost and trade-offs
| External (EWI) | Internal (IWI) | |
|---|---|---|
| Typical cost, 3-bed semi | Around £15,000 | Around £12,000 |
| Disruption inside | Very little, you can stay in | High, rooms out of use while work is done |
| Floor area | No change | Slightly smaller rooms |
| Outside look | New render or cladding finish | No change |
| Planning permission | Sometimes (see below) | Not usually (listed buildings aside) |
| Room by room? | No, whole elevations | Yes |
| Weatherproofing | Protects the brickwork | Outer wall gets colder, so moisture design matters |
Costs and trade-offs: Energy Saving Trust, solid wall insulation (updated 18 June 2026).
Not sure which wall you have? The Energy Saving Trust says homes built before about 1920 are more likely to have solid walls. On bare brick, an alternating pattern with some short brick ends showing points to a solid wall; a brick wall narrower than about 260mm is probably solid. If you have cavity walls, cavity wall insulation costs a fraction of EWI (around £2,200 for a typical home, says the Energy Saving Trust).
How much does solid wall insulation save?
The government measures this on real gas meters. In its latest National Energy Efficiency Data-Framework release (published 11 June 2026), DESNZ found that homes with new solid wall insulation used a median 17.3% less gas in the first year, a median saving of 1,857 kWh, across 2,411 homes in England and Wales.
At the Ofgem price cap gas rate for October to December 2026 (7.97p per kWh by Direct Debit), 1,857 kWh is worth about £148 a year (our calculation). Bigger, colder or oil-heated homes save more; smaller ones less.
Be clear-eyed about the maths: at £12,000–£15,000, wall insulation rarely pays for itself on bills alone. People do it for a warmer home, fewer cold walls and mould spots, a better EPC, and because the work can be free for eligible households or much cheaper when it rides on scaffolding you are paying for anyway.
Do you need planning permission for external wall insulation?
In England, EWI on a house can usually go ahead under permitted development, because the government treats solid wall insulation as an improvement, not an extension. The condition is that the materials are of a similar appearance to the existing outside of the house (GOV.UK householder permitted development technical guidance).
You will need to apply for planning permission when:
- The house is in a conservation area, National Park, the Broads, an Area of Outstanding Natural Beauty or a World Heritage Site. There, cladding any part of the outside with stone, artificial stone, pebble dash, render, timber, plastic or tiles is not permitted development.
- The finish would not look similar to the existing house, such as render over a bare brick terrace.
- It is a flat or maisonette, which has no householder permitted development rights.
- The building is listed: you will also need listed building consent, a separate application to your council.
Some councils remove these rights with an Article 4 direction, so ask your council's planning team first. A lawful development certificate gives you written proof if you want certainty. Rules differ in Scotland and Wales.
Building regulations
Both EWI and IWI count as "renovating a thermal element" under Approved Document L. If you insulate more than 50% of a wall, or more than 25% of the whole outside of the house, the whole wall should be brought up to a U-value of 0.30 where that is technically and economically feasible. The work needs building control sign-off, or an installer registered with a competent person scheme that can self-certify it.
External wall insulation problems: what can go wrong
Had EWI fitted under ECO4 or the Great British Insulation Scheme? The National Audit Office reported on 14 October 2025 that 98% of homes with external wall insulation under ECO4 and GBIS had major issues needing remediation (between 22,000 and 23,000 homes), and around a third of internal wall insulation did. The government is offering affected homes a free TrustMark "Find & Fix" audit, with problems fixed at no cost. Ofgem's helpline is 0808 169 4447. Only legitimate bodies such as Ofgem and TrustMark know your Unique Measure Reference Number, so don't let in anyone who can't quote it.
The disadvantages of external wall insulation to weigh up before you pay for it:
- Cost and payback. The most expensive insulation job on a house, with a long payback at full price.
- Moisture risk if it is badly detailed. Poor sealing at windows, eaves and the base of the wall lets water in behind the boards. The National Audit Office found widespread poor-quality fitting of wall insulation under ECO4 and GBIS.
- Old walls need breathable materials. The Energy Saving Trust and Historic England warn that traditional brick, stone and lime walls manage moisture by breathing, so the system has to be chosen to suit them.
- Ventilation. Sealing the walls makes the house more airtight, so your installer should check whether you need extra ventilation, and must not block airbricks or trickle vents.
- Not for every house. Homes exposed to extreme weather or flooding, or in poor condition, may not be suitable.
If you already have cavity wall insulation that is causing damp, that is a different problem with a different fix: see our guide to cavity wall insulation removal.
External wall insulation grants: who can get it free
This page is about cost. If your household is on a low income or a qualifying benefit, read our full external wall insulation grant guide first, because the cheapest EWI is the one you don't pay for. In short:
| Route | Where | What it can cover | Open until |
|---|---|---|---|
| Warm Homes: Local Grant | England | Insulation can be fully funded for low-income owners and private tenants in EPC D–G homes, through councils taking part | 31 March 2028 |
| ECO4 | Great Britain | Solid wall insulation for households on qualifying benefits; installers may ask for a top-up | 31 December 2026 |
| Home Energy Scotland Grant and Loan | Scotland | Up to 75% of the cost, with a grant of up to £7,500 for solid wall insulation plus an optional interest-free loan of up to £2,500; rural uplift available | Open |
| Nest | Wales | Free home improvements, including insulation, for eligible households | Open |
| 0% VAT | UK | No VAT on installed insulation, whoever pays | 31 March 2027, then 5% |
Sources: DESNZ Warm Homes: Local Grant policy guidance (July 2026); Ofgem ECO4; Home Energy Scotland; GOV.WALES; HMRC VAT Notice 708/6. Funding is limited and not guaranteed.
Two things that won't help: the new Warm Homes Loan does not fund insulation (DESNZ scheme rules), and the Great British Insulation Scheme ended on 31 March 2026. In Scotland, see energy grants in Scotland; for every insulation route on one page, see free insulation grants.
How to get a fair external wall insulation quote
- Fix the house first. Gutters, pointing, roof edges and any damp. A good installer will refuse to insulate over them.
- Use a TrustMark-registered installer. The Energy Saving Trust says external wall insulation should be fitted by a specialist trained by the approved system designer.
- Get at least three quotes and compare them per m² and line by line: scaffolding, roof-line extensions, sills, downpipes, meter boxes, finish and making good.
- Ask about planning and building control before you sign, and who is applying.
- Get the 25-year guarantee in writing. TrustMark solid wall installers offer one, backed by an insurer or by SWIGA, the Solid Wall Insulation Guarantee Agency.
- Check your grant route before you pay. If you might qualify, a funded install has to go through the scheme from the start.
Doing a whole-house job? Ask the same surveyor about loft insulation, underfloor insulation and room-in-roof insulation at the same visit. Wall insulation makes the house more airtight, so it is the moment to plan ventilation too.