Cavity wall insulation Cavity wall insulation installation

Fitting cavity wall insulation is one of the most cost-effective ways to improve your home's energy efficiency and reduce your energy bills. 

See our guide below on installing cavity wall insulation, or visit Which? Switch to see if you could save money on your bills by comparing energy prices.

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.

Cavity wall insulation costs and savings

See our page on cavity wall insulation cost and savings 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.

You might be eligible for free or discounted wall insulation. Check our insulation grants page to find out more.

How cavity wall insulation is installed

Cavity wall insulation illustration

Cavity walls can be filled with insulation in just two hours

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.

Which? members can find a insulator in your area recommended by other Which? members, using Which? Local - or you can join the discussion in our insulation forum using the panel at the top-right of this page.

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.

cavity wall graphic

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 FAQs 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 wall insulation installers recommended by Which? members using Which? Local.

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

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