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.
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.
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 for more details.
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.
Table notes: Injected polystyrene beads to wall, cavity width 100mm. Making good all holes on completion.
As you'll see in the table below, you could save up to £245 a year by insulating cavity walls.
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.
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.
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.
*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.