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Cavity wall insulation

Cavity wall insulation costs and savings

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Does your home have cavity walls? Find out how much it costs to get cavity walls insulated, and how much you could save on your heating bills.

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. 

Scroll down 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?.

What is cavity-wall insulation

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 (EST), it should cost between £330 and £725, depending on the size of your home. That makes it fairly cost-efficient – cavity-wall insulation should pay for itself within five years through the savings you’ll make on your heating bills.

When Which? investigated cavity-wall insulation sales practices in 2011, we uncovered some concerns about assessments, price differences and poor advice. Watch our undercover video about cavity-wall insulation damp problems for more details. 

To make sure you’re paying the right price for insulation and getting the right advice, see cavity-wall insulation installation.

How much does cavity-wall insulation cost?

We've worked with the Royal Institution of Chartered Surveyors*, 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 Subscriber only content Subscriber only content
Semi-detached Subscriber only content Subscriber only content
Detached Subscriber only content Subscriber only content
Table notes: Injected polystyrene beads to wall, cavity width 100mm. Making good all holes on completion.

Cavity-wall insulation savings

As you'll see in the table below, you could save up to £245 a year by insulating cavity walls.

Are you eligible for free cavity-wall insulation?

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, see our guide to insulation grants.    

Insulation and home energy-efficiency ratings

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.

Loft, roof and floor insulation

If 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 to draught proofing

You could also consider installing loft, roof 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.

RICS cost calculations

*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. Prices correct September 2019.

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