Cavity wall insulation

  How much could you save?

These are estimated figures based on insulating a gas-heated, semi-detached home with three bedrooms. The average installed cost is unsubsidised.

  Is cavity wall insulation suitable for your home?

Your home will usually be suitable for cavity wall insulation if:

• its external walls are unfilled cavity walls
• your cavity is at least 50mm wide
• the masonry or brickwork of your property is in good condition
• it is more than ten years old (most newer houses will have insulation already)
• the walls are not exposed to driving rain.

Are your cavity walls unfilled?

If your house was built in the last ten years or so, its walls are probably insulated already. To find out whether they are: 

• ask a registered installer for a boroscope inspection. They will drill a small hole in your external wall to see if your walls are hollow or filled. 
• check with your local authority's building control department - they might know if your cavity walls have been filled already.

Are your external walls easy to access?

Cavity wall insulation is blown into the cavity from the outside of a house. Every part of the wall must be filled with insulation, so it's important that the installer can reach all your external walls.

If your home's external walls are joined to another house, the installer will need to insert a cavity barrier to contain the insulation, so your neighbours aren't affected.

What if there is damp?

If you have any damp patches on your internal walls then they should not be insulated until the problem is sorted out. You should speak to a builder who specialises in damp prevention. 

How is insulation installed?   

To insulate your cavity walls, the installer drills small holes around 22mm in size at intervals of around 1m in the outside wall of your home. With specially designed equipment, they then blow insulation into the cavity. Once all the insulation is in, the installer fills the holes in the brickwork so you'll barely notice them.

Filling cavity walls is not a job you can do yourself: you will need to find a registered installer. A professional can do the job in around two hours for an average house with easily accessible walls; it should be simple, quick - and make no mess.

Finding an installer

Your installer should be a member of one of these organisations:

• the National Insulation Association (NIA) (Go to the NIA website)
• the Cavity Insulation Guarantee Agency (CIGA) (Go to the CIGA website)
• the British Board of Agrément (BBA) (Go to the BBA website).

Remember to also check that:

• your installer is signed up to a code of professional practice like the one provided by the NIA
• the installation is guaranteed for 25 years by CIGA.

What is the insulation made of?  

Cavity wall insulation can be made out of three types of materials:

• mineral wool
• beads or granules
• foamed insulants.

All three are manufactured according to British standards. Foam Insulation systems should be certified by the British Board of Agrément and installed according to strict guidance laid out in the associated BBA Certificates.

Find out more at the British Board of Agrément website.

What we recommend

Your installer will suggest the most suitable type of insulation for you but ask if they are using Energy Saving Trust Recommended insulation: this means it complies to British standards and it has a 25-year guarantee. Energy Saving Trust Recommended cavity wall insulation is the most energy efficient on the market so will save you money and energy. Ask your installer to look for the label to make sure you make the best choice.

Look for Energy Saving Trust Recommended insulation materials.