How much does cavity wall insulation cost in the UK?
Cavity wall insulation costs £1,200 on average in the UK. Most jobs fall between £400 and £3,500 for the house. Property size: Flat or small house £400 to £900; 3-bed semi £900 to £1,800; Large or detached £1,800 to £3,500. Prices reviewed June 2026.
Cavity wall insulation is priced mainly by the size of the property. It is injected into the gap between the outer and inner walls, so the wall area and number of external walls drive the cost.
Cavity wall insulation cost calculator
Use the calculator to price your cavity wall insulation in 2026. Adjust the options and area for a UK cost range. Nothing is sent anywhere.
Cavity wall insulation cost breakdown
Typical cavity wall insulation costs, by option:
| Property size | Typical UK cost |
|---|---|
| Flat or small house | £400 to £900 |
| 3-bed semi | £900 to £1,800 |
| Large or detached | £1,800 to £3,500 |
What's included in the price?
Typical cavity wall insulation prices include:
- Survey to confirm the cavities are suitable
- Drilling and injecting the insulation
- Making good the drill holes
- A guarantee, often the 25-year CIGA cover
What changes the price?
The things that move cavity wall insulation prices most:
Property size and number of external walls
Wall construction and the condition of the cavity
Access and scaffolding for taller walls
Whether a grant covers part or all of the cost
How the price is built up
Most of the total is the drilling and injection work itself, so the price tracks the wall area an installer has to fill. A flat or small house has fewer external walls to treat and sits near the £400 to £900 band, while a 3-bed semi with more wall to cover lands around £900 to £1,800. A large or detached house pushes towards the £1,800 to £3,500 top because there is simply more cavity to fill, and taller walls need access equipment. Wall construction and the condition of the cavity move the figure too, as a damp or debris-filled cavity needs clearing first. Where a grant covers part or all of the work, your share drops well below these numbers. Labour is the larger share on most jobs, usually around 60 to 70 percent of the total, with the mineral wool or bead material making up the rest, since the work is mainly a skilled crew drilling and injecting rather than fitting costly components.
Ways to keep the cost down
- Check your eligibility for ECO4 or the Warm Homes: Local Grant before you pay anything. If you qualify, the grant can cover part or all of the £400 to £3,500 cost, and this matters far more than shopping around on price.
- Get the whole property done in one visit rather than treating walls separately. The crew, drilling and clean-up are already set up, so filling all the cavities together keeps a 3-bed semi nearer the middle of its £900 to £1,800 band instead of paying twice.
- Fix any damp or clear a blocked cavity before booking. A cavity that needs clearing first adds cost and can push a job up a band, so sorting the wall condition in advance keeps the injection work straightforward.
- Get two or three quotes from installers registered with CIGA or the NIA. Prices are fairly consistent nationally, so a quote well above the tier for your property size is worth questioning rather than accepting.
Does where you live change the cost?
In London, cavity wall insulation typically costs around £1,600 for the house, about 30% above the UK average of £1,200. In the North, Scotland and Wales the guide figure is nearer £1,100.
| Region | From | Typical | Up to |
|---|---|---|---|
| Midlands / East (UK average) | £400 | £1,200 | £3,500 |
| London | £520 | £1,600 | £4,600 |
| South East / South West | £460 | £1,400 | £4,000 |
| North / Scotland / Wales | £370 | £1,100 | £3,200 |
Guide prices for the house, scaled with the same regional multipliers as the calculator. Not quotes.
Cavity wall insulation cost in major UK cities
| City | From | Typical | Up to |
|---|---|---|---|
| Belfast | £340 | £1,000 | £3,000 |
| Birmingham | £390 | £1,200 | £3,400 |
| Bristol | £440 | £1,300 | £3,900 |
| Cardiff | £380 | £1,100 | £3,300 |
| Edinburgh | £390 | £1,200 | £3,400 |
| Glasgow | £360 | £1,100 | £3,200 |
| Leeds | £370 | £1,100 | £3,300 |
| Liverpool | £370 | £1,100 | £3,200 |
| London | £520 | £1,600 | £4,600 |
| Manchester | £380 | £1,200 | £3,400 |
| Newcastle | £360 | £1,100 | £3,200 |
| Sheffield | £370 | £1,100 | £3,200 |
City guide estimates, scaled by local labour costs. Indicative averages for cavity wall insulation, not quotes.
Fairly consistent nationally. Grant eligibility affects what you pay more than where you live: ECO4 runs to 31 December 2026, and the Warm Homes: Local Grant is open in England.
Common questions
How much is cavity wall insulation for a 3 bed house?
A typical three bedroom semi costs roughly £900 to £1,800, before any grant. A flat is less and a large detached house more, because the price tracks the wall area.
Is cavity wall insulation worth it?
For a suitable home with clear cavities it usually pays back through lower heating bills. On very exposed or damp-prone walls it is worth a survey first, as it is not right for every property.
What are the problems with cavity wall insulation?
In the wrong wall it can cause damp: homes in exposed, wind-driven-rain locations or with poorly maintained brickwork are the risk cases, which is why a proper pre-install survey matters. Use an installer covered by the industry guarantee scheme (CIGA, 25 years), keep the certificate, and if a previous fill has failed, extraction is possible but costs more than the original install did.
How long does cavity wall insulation take to install?
Usually half a day for a typical house. The installer drills a pattern of small holes in the mortar joints, injects the insulation, and makes the holes good. There is no internal disruption, which is why cavity fill at £900 to £1,800 for a semi is such a cost-effective upgrade where the wall suits it.
What happens to cavity wall insulation after 25 years?
Good mineral wool or bead insulation installed correctly should last the life of the house, often 25 years or more, with no routine cost to you. Problems come from poor fitting or water getting in, which can let the material slump or hold damp. If that happens, extraction and re-fill is a separate job, roughly in the same £400 to £3,500 range as the original install depending on property size. A CIGA guarantee, standard on registered work, covers defects for 25 years.
Is there a government grant for cavity wall insulation?
Yes. ECO4 and the Warm Homes: Local Grant can cover part or all of the cost, and eligibility affects your final bill more than anything else on this page. ECO4 runs until 31 December 2026 and targets lower-income households on certain benefits. The Warm Homes: Local Grant is England only and covers privately owned homes with an EPC of D to G where household income is usually £36,000 a year or less, or where you live in a qualifying postcode. If you qualify, your share can fall well below the £400 floor, sometimes to nothing. Check before paying, as installers often handle the application. The Great British Insulation Scheme, which was the broader council-tax-band route, closed to new applications and ended on 31 March 2026.
How much does cavity wall insulation cost for a flat compared with a detached house?
A flat or small house is the cheapest at £400 to £900, because there is less external wall to fill and access is usually simple. A large or detached house runs £1,800 to £3,500, as it has far more cavity to treat and taller walls may need access equipment. A 3-bed semi sits in between at £900 to £1,800. The typical house lands near £1,200, so property size is the single biggest driver of the price.
Can I inject cavity wall insulation myself?
No, this is not a DIY job. Filling a cavity means specialist rigs to drill and inject mineral wool or beads evenly, and the labour is 60 to 70 percent of the £400 to £3,500 cost precisely because it is skilled crew work. Get it wrong and you leave cold gaps or, worse, cause damp bridging that is costly to put right. It also needs a registered installer for any guarantee or grant to stand.
Official guidance and sources
The rules and schemes referenced on this page come from these official UK sources. The price figures are Costwise's own; see how we price.
- Find energy grants for your home (Help to Heat) GOV.UK · The current list of government insulation and heating grants. The Great British Insulation Scheme ended on 31 March 2026.
- Warm Homes: Local Grant GOV.UK · England only. Covers cavity and solid wall insulation for eligible homes rated EPC D to G.
- Energy Company Obligation (ECO4) GOV.UK · It may also be covered by the Energy Company Obligation.
These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.