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Around a third of all heat lost from a poorly insulated home escapes through the walls, which means installing cavity-wall insulation is often one of the most cost-effective measures you can take to save energy in your home.
Wall insulation acts as a blanket that prevents heat from escaping through the walls, and uniformly spreads heat around the home. It can also help to stop your home getting too hot in summer.
The type of wall insulation you’ll need depends on whether your home has cavity or solid walls. If your home was built from 1920 onwards, it’s likely to have cavity walls.
Solid walls tend to be fortified with bricks laid across, rather than along, the wall. These will look like smaller, half-sized bricks from the front. A cavity wall will have all the bricks laid in the same direction, so they'll all look the same size.
Read on for more on cavity wall insulation costs. If you have solid walls, head to our separate guide to solid wall insulation.
Both types should be installed by a professional installer. Visit Which? Trusted Traders to find a local insulation expert who's been vetted by Which?.
You can search for a reliable local trader using our search tool below.
Cavity-wall insulation is injected through the outer wall of your home into the space between the inner and outer leaves of brickwork that make up cavity walls.
According to the Energy Saving Trust, cavity-wall insulation should pay for itself within five years through the savings you’ll make on your heating bills.
To make sure you’re paying the right price for insulation and getting the right advice, see cavity-wall insulation installation.
We've worked with the Royal Institution of Chartered Surveyors* (RICS), which publishes average building work and repair costs, to bring you the average cost for cavity-wall insulation.
We've also split these so you can look at the average costs for a terraced, semi-detached and detached house. Do bear in mind that costs will vary, depending on where you live in the country.
Only logged-in Which? members can view our recommendations in the table below. If you're not yet a member, you can get instant access by joining Which?.
House type | Price from | Price to |
---|---|---|
Terraced | ||
Semi-detached | ||
Detached |
Injected polystyrene beads to wall, cavity width 100mm. Making good all holes on completion. Data copyright RICS 2023, reproduced with permission. Data is current as of December 2023.
As you'll see in the table, you could save up to £370 a year by insulating cavity walls:
Type of property | Energy bill savings per year |
Detached House | £370 |
Semi-detached house | £210 |
Mid-terrace house | £130 |
Detached bungalow | £160 |
Mid-floor flat | £100 |
Estimates based on a gas-heated home. The average install cost is unsubsidised. Figures are based on fuel prices as of July 2024. Calculated by the Energy Savings Trust.
Yes, it may be possible to get a grant towards the cost of paying for cavity wall insulation, as well as other energy efficiency home improvements, from the Great British Insulation Scheme. You may be able to get support if your home:
Further help for multiple improvements may be available if:
Additionally, if your cavity-wall insulation is deemed ‘hard to treat’, you may be able to benefit from a subsidy under the Energy Company Obligation.
‘Hard to treat’ walls are those that are not straightforward to fill. That could be because they need remedial work or have already been partially filled, for example.
For more information on the grants that are available and how to apply, read our article: Find out whether you qualify for the Great British Insulation Scheme or Home Upgrade Grant
Fitting insulation is an effective way of raising your home’s energy-efficiency rating. This will come in handy when it comes to selling your home.
When you sell a home, you need to provide an Energy Performance Certificate (EPC). A home’s EPC shows an overall energy-efficiency rating, ranked from A-G. ‘A’ represents the most energy efficient properties and ‘G’ the worst. The EPC also contains advice on how to cut carbon emissions and fuel bills by making home improvements.
If you don't have insulation installed, the EPC will recommend the type and level of insulation required for maximum efficiency.
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Get a quoteIf you already have wall insulation, or want to make additional energy-saving improvements to make your home warmer and boost its EPC rating, there are a number of things you can do.
Quick fixes to stop draughts are often easy to make – such as using a draught excluder on your front door.
For more advice, see our expert guide on how to draught proof your home.
You could also consider installing loft insulation, roof insulation or floor insulation, or other energy-efficiency boosters such as fitting a jacket to your boiler and installing double glazing.
If you're thinking about installing double glazing, head to our double glazing company reviews.
*To arrive at the average prices above, RICS uses cost data from its Building Cost Information Service (BCIS) database, where costs are collated from a variety of sources and analysed.
Material costs are based on the best trade prices from a range of suppliers across the UK, which are then benchmarked to reveal the best national average. Labour rates are based on the current Building and Allied Trades Joint Industrial Council wage agreement. Data copyright RICS 2023, reproduced with permission. Data is current as of November 2023.