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Cavity wall insulation

Cavity wall insulation installation

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Cavity wall insulation installation

Do your home’s cavity walls need insulating? Learn how cavity-wall insulation is installed and whether your home would be suitable.

If your home’s got cavity walls, fitting cavity-wall insulation is one of the most cost-effective ways to improve your home’s energy efficiency and reduce your energy bills. 

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 rainwater 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. Which not only means your home’s not as cosy as it could be, but also means you’re spending more on energy to heat it up.

So it’s a good idea to get cavity-wall insulation installed. Keep reading to find out what you need to know.

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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 the cavity walls have already been insulated.

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. To find out more, watch our undercover insulation video

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.

Cavity wall insulation costs and savings

You could save up to £225 a year by installing cavity wall insulation. To find out how much you should pay for insulation and what kind of savings you should expect to see on your heating bills afterwards, see cavity wall insulation costs and savings.

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 trusted, local trader in your area with the help of Which? Trusted Traders. Click to use Which? Trusted Traders to find an insulation installer.  

You can also find a local registered installer by calling the Energy Saving Trust helpline on 0300 123 1234.