Cavity wall insulation Cavity wall insulation costs and savings

More than a third of all heat lost from an uninsulated home escapes through the walls, so it shouldn't be a surprise to learn that installing cavity wall insulation is often one of the most cost-effective measures you can undertake to save energy in your home.

Cavity wall insulation cost and savings

As you'll see in the table below, you could save up to £275 a year by insulating cavity walls.

Cavity wall insulation
Type of propertyInstallation costSavings per yearCO2 savings per year (kg)Payback time
Detached house (four bedrooms)£720£2751,1002-3 years
Semi-detached house (three bedrooms)£475£1606503 years
Mid-terrace house (three bedrooms)£370£1054303-4 years
Detached bungalow (two bedrooms)£430£1104504 years
Mid-floor flat (two bedrooms)£330£903603-4 years

Table notes: figures based on a typical gas-heated home. All data obtained from the Energy Saving Trust (EST).

A house before and after cavity wall insulation installation. Image courtesy of Horton Levi Ltd. These before and after images show the difference cavity wall insulation can make

How wall insulation works

Wall insulation acts as a blanket that prevents heat from escaping through the walls of your 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. Both types should be installed by a professional installer.

The thermal images on the right show the same house before and after cavity wall insulation was fitted. 

It shows that with insulation, there is less heat loss and the heat is more uniformly spread around the house.

Type of wall

What type of wall insulation you need depends on whether your property has solid or cavity walls. If you don't know what type of walls you have, check our wall illustration first.

If you have solid wall insulation, see our separate guide for information on solid wall insulation.

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.

It's cost effective - it costs between £330 and £720 depending on the size of your home, and should pay for itself in four years or under 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. To make sure you're paying the right price and getting the right advice, see our cavity wall insulation section and watch our undercover insulation installation video.

Free cavity wall insulation

People with cavity wall insulation that is defined as 'hard to treat' can benefit from subsidy under the Energy Company Obligation.

'Hard to treat' means walls that are not straightforward to fill because, for example, they need remedial work or have been already partially filled.

Our guide on insulation grants has more information on which grants are available and how to apply.

EPC certificate

An Energy Performance Certificate (EPC) shows how energy efficient a house is

Loft, roof and floor insulation

If you already have wall insulation, or want to make additional energy-saving home improvements, you could also consider installing loft, roof or floor insulation.

Other home energy-efficiency measures include stopping draughts, fitting a jacket to your boiler and installing double glazing.

Insulation and home energy efficiency ratings

An Energy Performance Certificate (EPC) is needed when you want to sell your house. A home's EPC shows an overall energy-efficiency rating for your home 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.

Fitting insulation is an effective way of raising your home’s energy-efficiency rating. 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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