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  • Quick and easy installation
  • Significant energy savings

What it is 

Many houses are built with walls made up of two layers – an outer and an inner leaf. The gap between, known as the cavity, can often be filled with insulation to make the house more efficient. 

If your home has cavity walls, and they're suitable for insulation, then you'll need a specialist company to insulate them. They will drill holes in the mortar joints of your outside walls and inject insulation through the holes until the cavity has been filled. The holes are then re-filled with mortar to match the original. 
The most common materials are: 

  • Mineral wool – like loft insulation rolls, but chopped up so it can be blown into the cavity
  • Polystyrene beads – small spheres of expanded polystyrene. A bonding agent is added so that the beads will stay in place.

Sometimes foam insulation is injected, and this then sets rigid inside the cavity. This is more expensive than standard cavity wall insulation, but can be used in many situations where standard materials aren't suitable. It's also a particularly effective insulant. 

Is it right for me? 

If your house was built between 1920 and 1995, then the chances are it was built with an uninsulated cavity in the wall, and it may be suitable for cavity wall insulation. 

Before about 1920, most houses in the UK were built with solid walls – that is, the outside walls were made of a single solid layer of brick or stone. After 1920 it became increasingly common to build houses with an inner and an outer leaf with an air gap in between. This is known as a cavity wall, as opposed to a solid wall with no air gap. 
From about 1982, some houses were built with insulation in the gap between the inner and the outer leaf. If your house was built after 1995 then it probably does have cavity walls but they are probably already insulated, and it is unlikely that adding any further insulation would be worthwhile. However, many houses built between 1982 and 2000 were built with uninsulated cavities, so it could be worth checking. 
Some homes are not built of standard brick, stone or concrete block. Cavity wall insulation is usually not suitable for these. 
Some homes built with uninsulated cavities are not suitable for standard insulation, including: 

  • Very narrow or uneven cavities
  • Areas with high exposure to driving rain
  • Areas with a high risk of flooding  

Some of these houses may be suitable for more expensive foam injection, but some may not be suitable for any form of cavity insulation. 
If you are in any doubt about whether you could have cavity wall insulation, ask a certified installer to visit. They can carry out a survey to determine if your walls are suitable and, if so, what materials can be used. 
If your house has solid walls, or any other wall type that is not suitable for cavity insulation, then it may still be possible to insulate it. 

Living with cavity wall insulation 

Once your walls are insulated, the only difference you should notice is that your home is easier and cheaper to heat. You should keep on top of standard home maintenance jobs to make sure that your roof and walls don’t leak and your gutters are working properly. This is important for any home, but it’s particularly important if you’ve had your walls insulated.