How to buy wall insulation Cavity wall insulation
Use a registered insulation installer to fit cavity wall insulation
Fitting cavity wall insulation is one of the most cost-effective ways to improve your home's energy efficiency.
Nearly 40% of homes in the UK with cavity walls have not yet been adequately insulated. If every household in the UK that could install cavity wall insulation did so, it would save around £1 billion a year – or enough energy to heat 900,000 homes for the same period.
It's a worthwhile investment and could save you up to £135 a year on your heating bills.
Cavity wall insulation costs and savings
This table shows how much it could cost to insulate cavity walls, how much you could save on your heating bills, and how long it'll take to recoup the cost of the insulation.
| Cavity wall insulation | |||
|---|---|---|---|
| Installation cost | Savings per year | CO2 savings per year | Payback time |
| £100-£350 | up to £135 | 550 kg | 9 months to 3 years |
Figures based on a typical gas-heated semi-detached three-bedroom house. Source: the Energy Saving Trust.
What is cavity wall insulation?
Most homes built in the past 100 years were built with two layers of wall, leaving a small space or 'cavity' between the two layers.
The purpose of the cavity is to help prevent rain water from penetrating through the outer wall to the inside of the property. However, unfilled cavities also let heat escape and could be responsible for 35% of all heat lost from your home.
How cavity wall insulation is installed
You’ll need a registered installer to fit cavity wall insulation – it's not a job you can do yourself.
Cavity walls are filled with an insulating material; commonly-used materials include mineral wool, polystyrene beads or foam. Insulating cavity walls will help trap heat and prevent warmth from escaping.
A registered installer will be able to check your property’s suitability for cavity wall insulation and recommend the best type. The insulation is blown into the wall cavity from the outside of your property through drilled holes. The holes are then filled in with materials that match your brickwork.
Cavity wall insulation normally takes around two hours to install, but this depends on the size of the house and other factors, such as ease of access.
Check whether your home is suitable for cavity wall insulation
If your home was built from 1920 onwards, it's likely to have cavity walls. The cavity should be at least 50mm wide and the walls need to be in good condition to be suitable for cavity wall insulation.
If your house was built in the past 10 years, it's likely that he cavity walls have already been insulated.
The graphic opposite shows the difference between cavity walls and solid walls. The pattern of the bricks can often be an indication of the type of wall you might have.
Some cavity walls – for example, those regularly exposed to wind-driven rain – are not suitable for cavity wall insulation. When Which? investigated insulation sales tactics in early 2011, we uncovered some bad practices that installers employ when giving advice about cavity wall insulation for a house prone to damp problems. Watch our undercover insulation video and find out what to watch out for when getting cavity wall insulation on our insulation FAQ page.
Finding a cavity wall insulation installer
Choose an insulation installer who is a member of The National Insulation Association (NIA), The Cavity Insulation Guarantee Agency (CIGA) or The British Board of Agrément (BBA).
You can find a local registered installer by calling the Energy Saving Trust advice centre on 0800 512 012. It will also be able to answer any questions you have about cavity wall insulation and advise you of any energy grants or financial help available to you.
You can also find wall insulation installers recommended by Which? members using Which? Local.
- Watch our video investigation into cavity wall insulation installers
- Find out about energy efficient grants and offers
- Read our wall insulation FAQs
