Cavity wall insulation

Un-insulated cavity walls cost you money. Up to 33 per cent of the heat produced in your home is lost through the walls.

The good news is that cavity wall insulation is quick, clean and relatively inexpensive and it could save you between £85 - £280 a year on your fuel bills, depending on your house type. It is the most cost-effective way of significantly reducing your energy costs. It could also reduce carbon emissions by 335kg-1150kgs per year. 

It will create an even temperature in your home, help prevent condensation on the walls and ceilings and can also reduce the amount of heat building up inside your home during summer hot spells.

It will normally cost around £345 to £600 to install depending on house type and will pay for itself in approximately 5 years.

What is cavity wall insulation?

Cavity wall insulation is injected into the cavity between the inner and outer leaves of brickwork that make up the external wall of your property. An installer will do this from the outside of your property. There are a variety of different insulating materials  although the material used will most likely be mineral wool or polystyrene beads, but they all work in the same way: by combining with the still captive air, the insulation acts as a barrier to heat loss. The installer will take roughly between two to three hours for a three bedroom semi-detached house.  The work will be guaranteed for 25 years by the Cavity Insulation Guarantee Agency (CIGA).

How do I know if my home is suitable?

First of all, check the age of your house. In most houses built after the 1920s, the external walls are made of two layers with a small air gap or 'cavity' between them. This means they are ‘cavity walls’ and the gap between them can be filled with insulating material to stop the warmth escaping to the outside.

Looking at the brick pattern of your outside walls can also help to identify cavity walls, as this will usually differ from solid walls.

 Generally speaking, your home will be suitable for cavity wall insulation if:

  • the external walls are unfilled cavity walls
  • the masonry and/or brick work is in good condition
  • your cavity is at least 35mm wide (or 50mm for some forms of insulation)
  • the walls are not exposed to driving rain
  • your house is not at risk of flooding

Houses built since the 1990s are likely to have insulated cavities.

In all cases if you’re thinking about cavity wall insulation, always check with a registered installer who will assess whether your home is suitable.

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

Check whether the installer is signed up to a code of professional practice and that the installation is guaranteed for 25 years by CIGA, or through an independent insurance-backed guarantee.